2.0 LITERATURE REVIEW - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/26235/3/2 literature revie… · declare bioequivalence, such as the individual bioequivalence criterion

Chapter 2 Literature Review

Pharmaceutical Medicine 5 Jamia Hamdard

2.0 LITERATURE REVIEW

2.1 HISTORICAL PERSPECTIVE OF BIOEQUIVALENCE STUDIES

2.1.1 Generic drug approval process

Pre-1984: The process for generic drug approval has evolved along with changes in

federal drug law and regulations. Before enactment of the Food, Drug, and Cosmetic

Act (FDCA) in 1938, significant regulatory barriers to generic competition in the

market did not exist. Manufacturers of such products (e.g., codeine sulfate,

phenobarbital) could formulate, manufacture, and sell their products without submitting

bioequivalence or efficacy data to the FDA. The 1938 Act established a “new drug”

category, requiring manufacturers to document the safety of a product to the FDA and

established a 60-day delay before marketing could proceed, absent FDA objection.

Until 1962, generic versions of post-1938 drugs were marketed based on a“general

recognition” of safety. Typically, this designation was based on a history of safe use of

the innovator product. Such generic products were designate as “not new drugs.” (The

drugs/biologic approval process, 1998).

2.1.2 Drug price competition and patent term restoration Act of 1984 (Hatch-

Waxman Act)

The dual purposes of the Hatch-Waxman Act were to encourage the development of

new innovator drugs by extending patent rights and to establish procedures facilitating

the approval of low-cost generic drugs. These amendments to the FDCA codified in

statute an abbreviated process (ANDA) for post-1962 drugs whereby a generic company

could gain approval of its version of a drug without repeating the expensive and lengthy

clinical trials used to establish safety and efficacy of the innovator drug (Drug Price

Competition and Patent Term Restoration Act of 1984). Products approved under an

ANDA must be pharmaceutical equivalents (i.e. have the same active ingredient(s),

route of administration, dosage form, and strength) as the reference drug. They must

also be bioequivalent and the manufacturer must supply other basic technical

information related to manufacturing of the product that is normally required of an

NDA (Federal Food, Drug and Cosmetic Act, section 505(j) (8)). Generic drugs are

pharmaceutical equivalents only with respect to their active ingredients. The binders,

diluents, and excipients (filler) in the formulation, as well as the method of

manufacture, may vary. The FDA considers drug products to be therapeutic equivalents

if they are pharmaceutical equivalents and are bioequivalent. The publication,



Approved Drug Products with Therapeutic Equivalence Evaluations (the “Orange

Book”), identifies drug products approved by the FDA on the basis of safety and

effectiveness and includes therapeutic equivalence evaluations for approved multisource

prescription drug products. For every multiple-source product, the Orange Book cites a

letter code that indicates the FDA’s evaluation regarding the therapeutic equivalence of

the product relative to the reference innovator or brand-name product. These drugs are

placed in one of two categories as follows: “A”-rated products are considered to be

therapeutically equivalent to other pharmaceutically equivalent products; “B- rated

products are considered not to be therapeutically equivalent to other pharmaceutically

equivalent products. Class AB is a subset of “A “and includes DESI drug products and

post-1962 drug products for which actual or potential bioequivalence problems have

been resolved and that the FDA now considers to be therapeutically equivalent. Most

new generic products are defined as having “potential” problems until data is submitted

to establish their bioequivalence (The Orange book, CDER 2003).

2.1.3 Generic drug scandal and FDA reaction

In 1989 federal investigators implicated several generic industry officials in the conduct

of fraud, obstruction of justice, and noncompliance with various manufacturing

procedures. The investigations also revealed that several FDA employees had accepted

illegal gratuities or other compensation in exchange for information and assistance that

gave certain firms an advantage in the approval process. Investigators also discovered

that 10 or more generic companies had submitted fraudulent data related to

bioequivalence, stability testing, and manufacturing protocols for some of their products

(Featured Report of American Medical association: Generic Drugs (A-02)). The FDA

reacted to these findings by reorganizing its generic drug operations and conducting

comprehensive inspections. FDA investigators reevaluated data from hundreds of

generic drug applications. More than 2,550 samples of the top 30 prescribed generic

drugs or about 30% of all generic drugs on the market were collected and laboratory-

tested, and the agency conducted intensive inspections of 36 of the largest generic drug

firms and 12 contract laboratories. The agency determined that only 27 samples, or

approximately 1% of those tested, did not comply with standards of potency,

dissolution, content uniformity, product identification, moisture determination, or

purity. The FDA also tested 429 samples representing at least three different batches of

so-called narrow-therapeutic-range drugs that were currently marketed.



These 24 drugs, made by 73 brand-name and generic drug manufacturers, were

selected because of their potential for adverse reactions or therapeutic failure if they

lacked bioequivalence. Only five of the samples (all aminophylline tablets) failed to

meet United States Pharmacopoeia standards. None of the defects in the generic drugs

were judged to pose a public health hazard.

2.1.4 Determination of bioequivalence

Originally, bioequivalence was based on a demonstration that simple mean

bioavailability parameters differed by less than 20% from the brand-name product. In

1977 this was modified to include a “power” approach that tested the null hypothesis

that the rate and extent of bioavailability of the generic product was similar to the

innovator product, and the power of the study was sufficient to detect at least a 20%

difference.

In 1986, the FDA adopted the currently used average bioequivalence approach, which

involves a comparison of means. For immediate-release oral dosage forms, the standard

average bioequivalence determination employs a single-dose crossover study, typically

conducted in a limited number of healthy volunteers (usually 24 to 36 adults). Results

are analyzed according to whether the generic product (test), when substituted for the

brand-name product (reference), is significantly less bioavailable, and alternatively,

whether the brand-name product, when substituted for a generic product, is significantly

less bioavailable (the two 1-sided tests). The core of the bioequivalence concept is an

“absence of a significant difference.” A difference > ±20% is viewed by the FDA as

significant. By convention, all data are expressed as a ratio of the average response

(AUC and Cmax) for test/reference, so the limit expressed in the second analysis is

125% (reciprocal of 80%). Tests are carried out using an analysis of variance and

calculating a 90% confidence interval (CI) for the average of each pharmacokinetic

parameter, which must be entirely within the 80% to 125% boundaries. The width of

the CI reflects, in part, the within subject variability of the test and reference products

(CDER, 1997).

A common misconception, among manufacturers of generic products, is that the

average values between the reference and test product can vary by -20/+25%, which

could lead to large differences in efficacy between multisource products. In fact, when

applying these statistical criteria to studies involving 20 to 40 subjects, generic products



whose mean arithmetic bioavailability parameters differ by more than 5% to 10% from

the reference product begin failing the CI requirement. The FDA’s Office of Generic

Drugs has conducted two large surveys to quantify the differences between generic and

brand-name products. The first, conducted on 224 bioequivalence studies submitted in

approved applications during 1985 and 1986, found an average difference in AUC

measures between reference and generic products of 3.5% (Nightingale et al. 1987).

2.1.5 Current FDA guidance

The FDA in 2000 issued a final guidance for industry entitled Bioavailability and

Bioequivalence Studies for Orally Administered Drug Products–General

Considerations. In this guidance, the agency recommended non-replicated

bioequivalence study designs for most orally administered immediate-release drug

products and replicated bioequivalence study designs for modified-release dosage forms

(CDER, 2000). The guidance maintains the average bioequivalence criterion but allows

the option for a sponsor to provide rationale a priori for using another criterion to

declare bioequivalence, such as the individual bioequivalence criterion for highly

variable drug products. An additional concern with bioequivalence testing is that, with

certain drugs, it is the peak effect and not AUC that is important for the therapeutic

response or ADRs. This guidance was revised recently and recommended use of the

partial AUC as an early exposure measure instead of Tmax to address these concerns

(Bioavailability and Bioequivalence Studies for Orally Administered Drug Products--

General Considerations, CDER, 2003).

2.2 FDA REQUIREMENTS FOR BRAND-NAME AND GENERIC DRUGS

It is believed that anything which cost more is of better quality than the cheaper one.

The same is also true in case of therapeutic interventions. In general, innovator product

is believed to be better than the generic products. But FDA states that in the case of

generic drugs, this is not true. According to OGD (FDA's Office of Generic Drugs),

"The standards for quality are the same for brand name and generic products." Much of

FDA's review of generic drugs and brand name drugs is the same, as can be seen from

“FDA Requirements for Brand-Name and Generic Drugs" Table 2.1 [FDA-Available

at: http://www.fda.gov/cder/consumerinfo/generic_equivalence.htm].

There are eight major parts to the FDA's review of a firm's application to market a

generic drug:



1. There must be an FDA-approved brand-name drug that is the reference for the

proposed generic. The generic must have the same active ingredient or ingredients

and the same labeled strength as this reference product. It must have the same

dosage form-tablets, patches and liquids are examples of dosage forms. It must be

administered the same way, for example, swallowed as a pill or given as an

injection.

2. The manufacturer must show the generic drug is "bioequivalent" to the brand-name

drug.

3. The generic drug's labeling must be essentially the same as that of the approved

drug.

4. The firm must fully document the generic drug's chemistry, manufacturing steps,

and quality control measures. Each step of the process must be detailed for FDA

review.

5. The firm must assure the FDA that the raw materials and the finished product

meet USP specifications, if these have been set.

6. The firm must show that its generic drug maintains stability as labeled before it can

be sold. Once on the market, the firm must continue to monitor the drug's stability.

The firm must show that the container and its closure system won't interact with the

drug. Firms making sterile drugs must submit sterility assurance data showing

microbiologic integrity of these products.

7. The firm must provide a full description of the facilities it uses to manufacture,

process, test, package, and label and control the drug. It must certify that it

complies with federal regulations about current good manufacturing practices and

undergo FDA inspection of the manufacturing facility to assure compliance.

8. Before FDA approves a generic drug, it usually conducts an inspection at the

proposed manufacturing site to make sure the firm is capable of meeting its

application commitments and to ensure the firm can manufacture the product

consistently.



Table 2.1: Similar FDA Requirements for Brand-Name and Generic Drugs

FDA RequirementsBrandDrug

GenericDrug

For reformulations of a brand-name drug or generic versions of a drug, FDAreviews data showing the drug is bioequivalent to the one used in the originalsafety and efficacy testing.FDA evaluates the manufacturer's adherence to good manufacturing practicesbefore the drug is marketed.

FDA reviews the active and inactive ingredients used in the formulationbefore the drug is marketed.

FDA reviews the actual drug product.

FDA reviews the drug's labeling.

Manufacturer must seek FDA approval before making major manufacturingchanges or reformulating the drug.

Manufacturer must report adverse reactions and serious adverse healtheffects to the FDA.

FDA periodically inspects manufacturing plants.

FDA monitors drug quality after approval.

a number of misconceptions about generic drugs still persist among physicians and

patients [FDA Ensures Equivalence of Generic Drugs, Jan 6, 2003. Available at:

http://www fdagov/cder/consumerinfo/generic equivalence html]. Some myths and facts

are as follow:

Myths and Facts about Generic Drugs

MYTH: Generics are not as potent as brand-name drugs.

FACT: FDA requires generics to have the same quality, strength, purity, and stability as

brand-name drugs.

MYTH: Generic drugs just won't do the job as well as brand-name drugs.

FACT: Under the new law, generic drugs must be bioequivalent to their brand-name

counterparts to gain FDA approval. That means that the generics must contain the

same active ingredients and must be identical in strength, dosage form (tablet, solution,

etc.), and route of administration (for example, taken by mouth or through injection).

Further, they must release the same amount of drug into the body as the brand-name

drug.

MYTH: Generics take longer to act in the body.





GenericDrug












are as follow:




brand-name drugs.







drug.






GenericDrug












are as follow:




brand-name drugs.







drug.




FACT: The firm seeking to sell a generic drug must show that its drug delivers the same

amount of active ingredient in the same timeframe as the original product.

MYTH: Brand-name drugs are made in modern manufacturing facilities, and generics

are often made in substandard facilities.

FACT: FDA allows no drugs to be manufactured in substandard facilities. FDA officials

inspect more than 5,000 drug plants a year to ensure that standards are met. Generic

firms have state-of-the-art plants that compare favorably with those of brand-name firms.

(In fact, brand-name firms account for an estimated 70 percent to 80 percent of generic

drug production, making duplicate versions of their own or other brand-name

companies' drugs, but selling them without the brand name.

MYTH: Generics are not as safe as brand-name drugs.

FACT: FDA requires that all drugs be safe and effective and that their benefits

outweigh their risks. Since generics use the same active ingredients and are shown to

work the same way in the body, they have the same risk-benefit profile as their brand-

name counterparts.

MYTH: Generic drugs are likely to cause more side effects.

FACT: There is no evidence of this. FDA monitors reports of adverse drug reactions

and has found no difference in the rates between generic and brand-name drugs.

MYTH: Generic manufacturers only have to prove that the active ingredients in their

products get to the bloodstream. That doesn't mean that their products are used by the

body in the same way.

FACT: When the same amount of the active ingredients of the generic version gets into

the bloodstream at the same rate as the brand-name version, there is no scientific

reason to believe that the effects of the two drugs will differ.

MYTH: Most drugs are tested for bioequivalence in healthy young volunteers, yet 25

percent of all prescription drugs are taken by the elderly who don't react the same to

drugs.

FACT: While the elderly may often absorb and process (metabolize) drugs differently

than younger people, there is no proof that drugs will perform differently in them.

Further, it isn't ethical to force already weakened or disabled patients to give blood

samples and face the other discomforts of bioequivalence testing. Further, such patients



cannot be used in bioequivalence testing because they are virtually always taking other

drugs concurrently.

MYTH: FDA requires that brand-name manufacturers test new drugs in thousands of

patients, but it lets generic firms get by with tests in only 20 or 30 healthy volunteers.

FACT: Generic drugs are duplicates of products that have already been tested for safety

and effectiveness. Therefore, generic manufacturers need only prove to FDA that their

drug behaves the same way in the body as the original version. That requires only small-

scale tests. In fact, the same small-scale testing is done for brand-name drugs whenever

they are reformulated.

Because of the stringent regulations and complete assurance of quality of generic

products, by the US FDA, there is increased tendency of switchover from brand to

generic products. This promotion of generic use has resulted in huge cost saving (30% -

80%) on one hand, but ended with increased number of counterfeit/substandard drug

products on the other hand. This may be due to fact that drug regulations in most of

the developing countries are still not as stringent as in USA or European Union. For

example, the dissolution procedures, specified by the United States Pharmacopoeia

(USP); to test batch-to-batch uniformity, to detect manufacturing or process variation

that might influence the bioavailability and to document formulation bioequivalence,

are still not in practice in many of the developing countries.

A generic copy of reference drug must contain identical amounts of the same active

ingredients in the same dose formulation and route of administration, as well as meet

standards for purity, quality and identity. Some inactive ingredients such as binders and

fillers are allowed to differ, but must occur in the similar ratio to the active compound

as that observed in the brand name drug [Federal Register 1999], moreover, all the

inactive ingredients used in generic product must be approved with defined purity &

quality. This is where many smaller manufacturing units (>10000) differ from the bigger

one (over 100 USFDA approved) in India.

Medical profession has also realized the problem of wide variations in the therapeutic

effectiveness of various marketed brands of oral formulations containing the same

active ingredient in equal amounts. A number of patients with a history of good results

on brand name drugs observed difficulties when a generic was substituted to decrease

the cost of therapy.



Doctors in India are unlikely to prescribe unbranded generics despite two advisories

from the Medical Council issued in 2012 and 2013 urging them to do so, some private

and government doctors have said.

Krishan Kumar Aggarwal, a senior cardiologist in New Delhi who is also head of the

ethics committee of the Delhi Medical Council, told the BMJ: “Doctors in India are

already prescribing generic drugs, but through their brand names. If the authorities want

us to prescribe drugs through chemical names, why do they allow so many brand names

and why are there such wide price variations?” The first step should be to ensure

quality standards, quality monitoring, and quality assurance—unless doctors become

convinced [that] there is uniform quality, independent of the source of the compound, I

don’t expect doctors in India will routinely write out prescriptions with chemical names

of drugs,” Kapoor told the BMJ.

Regardless of the quality concerns, the idea to prescribe using chemical names has

some supporters, including doctors who say that the Medical Council’s advisories are a

reminder of the code of ethics physicians are expected to follow. For example, Amar

Jesani, a physician and editor of the Indian Journal of Medical Ethics, said that the

quality argument was “a hoax” at times conveniently used to prescribe specific brands.

“Doctors in India rarely think about price considerations,” Jesani told the BMJ. “With

generic prescriptions, at least consumers can demand cheaper drugs—let consumers

decide and fight it out with chemists.”

Figures from the Monthly Index of Medical Specialities (MIMS), India, suggest that 10

tablets of unbranded cetirizine, a second-generation antihistamine, were available in

2012 for about 1.50 rupees (£0.017; €0.019; $0.025), while a branded generic product

was sold at 27 rupees, and a branded version cost 39 rupees.( Zuzanna Fimińska July 02

2013)



BIOAVAILABILITY AND BIOEQUIVALENCE

2.3 BIOAVAILABILITY

Bioavailability is defined by the US-FDA as the rate and extent to which the active

ingredient or active moiety is absorbed from a drug product and becomes available at

the site of action. For drug products that are not intended to be absorbed into the

bloodstream, bioavailability may be assessed by measurements intended to reflect the

rate and extent to which the active ingredient or active moiety becomes available at the

site of action [Bioavailability and Bioequivalence Studies for Orally Administered Drug

Products--General Considerations. CDER, 2003].

The EMEA guidance defines Bioavailability as the rate and extent to which the active

substance or active moiety is absorbed from a pharmaceutical form and becomes

available at the site of action [Note for guidance on the investigation of bioavailability

and bioequivalence, EMEA].

The CDSCO, India, defines Bioavailability as the relative amount of drug from an

administered dosage form which enters the systemic circulation and the rate at which

the drug appears in the systemic circulation.

2.3.1 Types of bioavailability

Bioavailability can be classified into four different types depending on the purpose of

the study and scientific questions to be solved [Ritschel and Kearns 1998].

2.3.1.1 Absolute bioavailability

Absolute bioavailability is the ratio of the total area under the blood level time curve

upon extra vascular route of administration to the area under the blood level time curve

upon intravenous administration, corrected for the difference in the dose size.

Absolute bioavailability = AUC extravascular x dose i.v. / AUC i.v.x dose extravascular

2.3.1.2 Relative bioavailability

The relative bioavailability is the rate and extent of the bioavailability of a drug from two

or more different dosage forms given by the same route of administration. For

determination of rate and extent, blood level or urinary excretion data upon single or

multiple dosing can be used. According to the FDA regulation the standard used in this



procedure is an approved marketed drug product, a solution of the drug or suspension

of the micronized drug.

Relative bioavailability = AUCof A / AUC of B

Where B is the reference standard.

2.3.1.3 Relative optimal bioavailability

This term was suggested for optimizing extent and rate of bioavailability for a drug

product during the development phase.

For determination of EBA rel. opt, the active drug is administered in aqueous solution

without the addition of any further excipients by the same route which is intended for

the drug product under development.

EBA rel. opt. = AUC (drug + vehicle; granules; tablets) / AUC solution x 100

2.3.1.4 Bioavailability in presence of first-pass effect

Drugs showing a first-pass effect may result in considerably lower blood level time

curves. Even though the entire parent drug was absorbed from the site of

administration, it does not reach systemic circulation in unchanged form.

The fraction of a peroral (po) or in part, rectal dose reaching systemic circulation F,

under the assumption of otherwise linear kinetics can be described by eqn.

F = 1- Dose iv x fm / LBF x AUCiv x 60 x

LBF - liver blood flow

fm - fraction of drug metabolised in liver

- Ratio of the concentration of the drug in whole blood to that in plasma

2.3.2 Different approaches used for measurement of bioavailability

There are several direct and indirect methods for the measurement of bioavailability in

humans. The selection of method depends on the purpose of the study, analytical

method and nature of the drug product. The methods can be broadly divided into two

categories: (a) Pharmacokinetic methods (b) Pharmacodynamic methods.



2.3.2.1 Pharmacokinetic Methods

These are very widely used and are based on the assumption that the pharmacokinetic

profile reflects the therapeutic effectiveness of a drug. Thus these are indirect methods.

The two major pharmacokinetic methods are;

Plasma level-time studies

Unless determination of plasma drug concentration is difficult or impossible, it is the

most reliable method and method of choice in comparison to urine data. This method

is based on the assumption that two dosage forms that exhibit “superimposable” plasma

level-time profiles in a group of subjects should result in identical therapeutic activity.

The three parameters of plasma level-time studies, which are considered important for

determining bioavailability, are:

1. Cmax: The peak plasma concentration that gives an indication whether the drug is

sufficiently absorbed systemically to provide a therapeutic response.

2. Tmax: The time of peak plasma concentration corresponds to the time required

to reach maximum drug concentration after drug administration. At Tmax,

absorption is maximized and the rate of drug absorption equals the rate of drug

elimination. When comparing drug products, tmax can be used as an approximate

indication of the drug absorption rate.

3. AUC: The area under the plasma level-time curve that gives a measure of the

extent of absorption or the amount of drug that reaches the systemic circulation.

The extent of bioavailability can be determined by equation-

F = AUCoral Div / AUCiv Doral

Urinary excretion studies

This method of assessing bioavailability is based on the principle that the urinary

excretion of unchanged drug is directly proportional to the plasma concentration of

drug. This method is particularly useful for drugs extensively excreted unchanged in the

urine. The method involves collection of urine at regular intervals for a time span equal

to 7-10 biological half-lives, analysis of unchanged drug in the collected sample and

determination of the amount of drug excreted in each interval and cumulative amount

excreted. The three major parameters examined in urinary excretion data obtained with

a single dose study are:



1. (dxu/dt)max: The maximum urinary excretion rate, is obtained from the peak of

plot between rate of excretion versus midpoint time of urine collection

period. It is analogous to Cmax derived from plasma level studies since the rate

of appearance of drug in the urine is proportional to its concentration in the

systemic circulation.

2. (tu)max: The time for maximum excretion rate, is analogous to the tmax of plasma

level data. Its value decreases as the absorption rate increases.

3. Xu: The cumulative amount of drug excreted in the urine, is related to the

AUC of plasma level data and increases as the extent of absorption

increases.

The extent of bioavailability can be calculated using equation given below:

F = (Xu) oral Div / (Xu) iv Doral

2.3.2.2 Pharmacodynamic Methods

These methods are complimentary to pharmacokinetic approaches and involve direct

measurement of drug effect on a physiologic process, as a function of time.

The two pharmacodynamic methods involve determination of bioavailability from:

(a) Acute pharmacologic response

(b) Therapeutic response

Acute pharmacologic response

In some cases quantitative measurement of a drug is difficult, inaccurate or non

reproducible. In such cases an acute pharmacologic effect such as effect on pupil

diameter, heart rate or blood pressure can be a useful index of drug bioavailability.

Bioavailability can be determined by construction of pharmacologic effect-time curve as

well as dose-response graphs. The method requires measurement of responses for at

least 3 biological half-lives of drug in order to obtain a good estimate of AUC.

Therapeutic response

Theoretically the most definite, this method is based on observing the clinical response

to a drug formulation given to patients suffering from disease for which it is intended to

be used. Bioequivalent drug products should have the same systemic drug

bioavailability and therefore the same predictable drug response.



However, variable clinical responses among individuals that are unrelated to

bioavailability might be due to differences in the pharmacodynamics of the drug.

Various factors affecting pharmacodynamic drug behaviour may include age, sex, drug

tolerance, drug interactions and unknown pathophysiologic factors.

2.3.2.3 In vitro methods

Under certain circumstances, product quality BA and BE can be documented using in

vitro approaches. For highly soluble, highly permeable, rapidly dissolving, orally

administered drug products, documentation of BE using an in vitro approach

(dissolution studies) is appropriate based on the biopharmaceutics classification system

(BCS) [CDER, 2000]. The preferred dissolution apparatus is USP apparatus I (basket)

or II (paddle), used at compendially recognized rotation speeds (e.g., 100 rpm for the

basket and 50-75 rpm for the paddle). In other cases, the dissolution properties of

some ER formulations may be determined with USP apparatus III (reciprocating

cylinder) or IV (flow through cell).

2.3.3 Factors affecting bioavailability

Bioavailability of any product varies with many factors, which are conveniently divided

into drug factors and host factors (Brahmankar and Jaiswal 1999). The drug factors

include physicochemical properties of drug substance and dosage form characteristics.

The host factors include age, blood flow to gastrointestinal tract (GIT), presence of

food or other contents in GIT, GIT pH, gastric emptying, disease state and pre-

systemic metabolism by enzymes in the gut wall or in the liver. The various factors

affecting bioavailability of drugs can be classified as shown in Table 2.2.

2.3.3.1 Physicochemical properties of drug

Drug solubility and dissolution rate

Dissolution is the rate-determining step (RDS) for hydrophobic, poorly aqueous soluble

drugs like griseofulvin and spironolactone; absorption of such drugs is said to be

dissolution rate-limited. If the drug is hydrophilic with high aqueous solubility e.g.

cromolyn sodium or neomycin, then dissolution is rapid and the RDS in the absorption

of such drugs is rate of permeation through the bio-membrane. Adsorption of such

drugs is said to be permeation rate limited or transmembrane rate limited. Fig. 2.1

shows a schematic representation of this concept.



Fig. 2.1: Schematic presentation of absorption processes of oral dosage forms

Particle size and effective surface area

Particle size and surface area of a solid drug are inversely related to each other. Particle

size is of importance for drugs of low solubility. The critical point is solubility of less

than 0.3 percent. With decreasing particle size, the surface area increases, thus

increasing the area of solid matter being exposed to the dissolution media and, hence,

dissolution rate increases. However, the actual solubility does not significantly change

with particle size reduction (micronization) in the range used in pharmaceutical

manufacture. The following eqn. describes the dissolution rate:

dc/dt = k. a. (Cs-Ct)

dc/dt = dissolution rate (amount per unit time) (Noyes Whitney equation)

k = constant depending on intensity of agitation, temperature, structure of solid surface,

and diffusion coefficient

a = surface area of undissolved solute

Cs = solubility of drug in solvent

Ct = concentration of dissolved drug at time t

Examples of drugs for which therapeutic differences have been found depending on

particle size are: amphotericin, aspirin, bishydroxycoumarin, chloramphenicol, digoxin,

acetonide, griseofulvin, meprobamate, nitrofurantoin, phenobarbital, phenothiazine,

prednisolone, procaine penicillin, reserpine, spironolactone, sulfadiazine and

tolbutamide (Ritschel and Kearns, 1998).

SolidDosageForm

SolidDrug

Particles

Disintegration

Deaggregation

Dissolution

RDS for Lipophilic drugs

Drug inSolution atabsorption

Site

Permeation acrossbiomemebrane

RDS for Hydrophobic drugs

Drug inthe

body



Polymorphism and amorphism

Polymorphism is the phenomenon that a drug may exist in different crystalline forms,

polymorphs. The most stable form has highest stability but lowest dissolution rate. The

least stable form usually has the most rapid dissolution rate. The unstable (metastable)

forms convert more or less slowly into the more stable form. e.g. chloramphenicol

palmitate appears in three different polymorphs, but only polymorph B is biologically

active, since the other forms do not dissolve and are not hydrolysed. The polymorphs

differ from each other with respect to their physical properties such as solubility,

melting point, density, hardness and compression characteristics. Some drugs can exist

in amorphous form (i.e. having no internal crystal structure). In general, the amorphous

state is more soluble and has a higher dissolution rate than the crystalline form. The

crystalline form requires a higher amount of energy to free a molecule of drug from it

than does the amorphous form. e.g. amorphous novobiocin and amorphous

chloramphenicol esters are biologically active while their crystalline forms are inactive.

Salt form of a drug

Most drugs are either weak acids or weak bases. One of the easiest approaches to

enhance the solubility and dissolution rate of such drugs is to convert them into

their salt forms. At a given pH, the solubility of a drug, whether acidic/basic or its

salt form, is a constant.

Drug pKa and lipophilicity and GI pH

The pH Partition theory explains in simple terms, the process of drug absorption from

the GIT and its distribution across all biologic membranes. The theory states that for a

drug compound of molecular weight greater than 100, which are primarily transported

across the biomemebrane by passive diffusion, the process of absorption is governed

by:

1. The dissociation constant (pKa) of the drug.

2. The lipid solubility of the unionized drug (a function of drug Ko/w).

3. The pH at the absorption site.

Lipophilicity and drug absorption

The pKa of a drug determines the degree of ionization at a particular pH and that only



the unionized drug, if sufficiently lipid soluble, is absorbed into the systemic circulation.

Thus, even if the drug exists in the unionized form, it will be poorly absorbed if it has

poor lipid solubility. Ideally, for optimum absorption, a drug should have sufficient

aqueous solubility to dissolve in the fluids at the absorption site and lipid solubility (Ko/w)

high enough to facilitate the partitioning of the drug in the lipoidal membrane and into

the systemic circulation. Hence, a perfect hydrophilic-lipophilic balance (HLB) should

be there in the structure of the drug for optimum bioavailability.

2.3.3.2 Patient related factors

Age

In infants, the gastric pH is high and intestinal surface and blood flow to the GIT is low

resulting in related absorption pattern in comparison to adults. In elderly persons,

causes of impaired drug absorption include altered gastric emptying, decreased

intestinal surface area and GI blood flow.

Gastric emptying

Apart from dissolution of a drug and its permeation through the biomembrane, the

passage from stomach to the small intestine, called as gastric emptying can also be rate

limiting step in drug absorption because the major site of drug absorption is intestine.

Thus generally speaking, rapid gastric emptying increases bioavailability of a drug.

Rapid gastric emptying is desired where:

A rapid onset of action is desired e.g. sedatives

Dissolution of drug occurs in the intestine e.g. enteric coated dosage forms

The drugs are not stable in the gastric fluids e.g. penicillin G, and erythromycin

The drugs is best absorbed from the distal part of the small intestine e.g. vitamin

B12

Intestinal Transit

Since small intestine is the major site for absorption of most drugs, long intestinal transit

time is desirable for complete drug absorption. The residence time depends upon the

intestinal motility or contractions. The mixing movement of the intestine that occurs

due to peristaltic contractions promotes drug absorption, firstly, by increasing the drug-

intestinal membrane contact, and secondly, by enhancing the drug dissolution especially

of poorly soluble drugs, through induced agitation.



Blood flow to the GIT

GIT is extensively supplied by blood capillary network and the lymphatic system. The

absorbed drug can thus be taken by the blood or the lymph. Since the blood flow rate

to the GIT (splanchnic circulation) is 500 to 1000 times (28% of cardiac output) more

than the lymph flow, most drugs reach the systemic circulation via blood whereas only a

few drugs, especially low molecular weight, and lipid soluble compounds are removed

by lymphatic system. The high perfusion rate of GIT ensures that once the drug has

crossed the membrane, it is rapidly removed from the absorption site thus maintaining

the sink conditions and concentration gradient for continued drug absorption.

Table 2.2: Factors affecting absorption of a drug from its dosage form [Brahmankar and

Jaiswal 1999]

PHARMACEUTICAL FACTORS PATIENT RELATED

Physicochemical properties ofdrug substances

Dosage form relatedfactors

Drug solubility and dissolutionrate

Disintegration time Age

Particle size and

effective surface areaDissolution time Gastric emptying time

Polymorphism and amorphism Manufacturing variables Intestinal transit time

Hydrates / solvates Pharmaceuticalingredients

GIT pH

Salt form of the drug Nature and type ofdosage form

Disease states

Lipophilicity of the drug Product age and storageconditions

Blood flow through GIT

pKa of the drug and p

Gastrointestinal contents:

Other drugs, Other normal GIcontents, Food, Fluids

Drug stability

Pre-systemic metabolism

by: Luminal enzymes, Gut wallenzymes, Bacterial enzymes,

Hepatic enzymes



2.4 BIOEQUIVALENCE

Bioequivalence (BE) is a relative term. It is defined as the absence of significant

difference in the rate and extent to which the active ingredient or active moiety in

pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site

of drug action when administered at the same molar dose and under similar conditions

in an appropriately designed study (CDER, 2003). In bioequivalence studies, the

primary question is to compare measures of release of drug substance between the test

and reference product. Hence bioequivalence is primarily a product quality question.

As product’s bioavailability and bioequivalence are closely related, similar approaches

for establishing BA and BE may be followed.

2.4.1 Historical perspective of bioequivalence

The fundamental mission of the Drug Regulatory Agencies is protection of the

consumers. The Drug Regulations require the regulatory agencies to assess safety,

efficacy and quality of all new drug formulations, before they are marketed.

Bioequivalence studies are performed to demonstrate that two pharmaceutically

equivalent products are equal in rate and extent of absorption in vivo. Following on

from developments in the pharmaceutical industry and government mandates in the

1970's and 1980's and since the early 1990's, average bioequivalence has served as the

international standard for demonstrating that two formulations of drug product will

provide the same therapeutic benefit and safety profile when used in the marketplace.

Population (PBE) and Individual (IBE) bioequivalence has been the subject of intense

international debate since methods for their assessment were proposed in the late

1980's. Guidance has been proposed by the Food and Drug Administration of the

United States government for the implementation of these techniques in the pioneer

and generic pharmaceutical industries. Implementation of these techniques may follow

a data collection period to evaluate the operating characteristics, efficiency, and metrics

involved in PBE and IBE assessment. The historical milestones of drug law are

summarized in Table 2.3.



Table 2.3: Chronology of regulatory events [Modified from Truman HS, 1992]

Year Event

1902 Biologics Control Act

1906 Pure Food and Drugs Act / Wiley Act

1912 Shirley Amendment to Pure Food and Drugs Act- No false claim

1936 Elixir Sulfanilamide Disaster

1938 Food Drug & Cosmetics Act: FDA control over safety of new drugs

1951 Durham-Humphrey Amendments to FD & C Act: Prescription drugs

1961 Thalidomide disaster in Europe

1962 Kefauver-Harris amendment-FDA Control over both safety and efficacy of drugs-

1963 Initial Good Manufacturing Practices (GMP) regulations

1974 World Health organization, recommendations for conduct of bioavailability studies

1974 Dissolution test adopted as standard for in vitro comparison of bioavailability in UK

1977 US FDA regulations for approval of BE. The + 20% rule with p<0.05

1983 Orphan drug act

1984 ANDA for generics approval-Waxman-Hatch act (Drug price competition and patentterm restoration act)

1985 New 80-125% for CI law for approval of generic products

1987 Standard 2x2 crossover test design for BE studies

1989 Generics scandal in USA. Concern for adequate documentation and validation of BEstudies

1992 90-111% CI for narrow therapeutic index drugs: Canadian FDA

1995 EEC-70-143% limit for Cmax only for drug with wide safety margin

1999 Draft regulations for BE studies: In India

2005 Regulations for BE studies: In India

2.4.2 Need for bioequivalence study

2.4.2.1 Bioequivalence for first entry products

BE studies may be useful during drug development and registration for a first entry

product during the Investigational New Drug (IND) or New Drug Application (NDA)

period to establish links between (i) early and late clinical trial formulations (ii)

formulations used in clinical trial and stability studies, if different (iii) Clinical trial

formulations and to be marketed drug products (iv) other comparisons as appropriate.

In each comparison, the new formulation or new method of manufacture is the test

product and the prior formulation or method of manufacture is the reference product.



2.4.2.2 Bioequivalence for interchangeable multi-source products

BE studies are a critical component of Abbreviated New Drug Applications (ANDA).

The purpose of these studies is to compare relative BA measures between a

pharmaceutically equivalent multi-source test product and the corresponding reference

pioneer product. The innovator product is termed as reference listed drug (RLD).

Together with the determination of pharmaceutical equivalence, demonstrating BE

allows a regulatory conclusion of therapeutic equivalence and interchangeability

between the test and reference product [The Orange book, CDER, 2007].

2.4.2.3 Bioequivalence for post approval changes

Generally specifications are adequate to assure product quality on the assumption that

no important change occurs post-approval. In the presence of major changes in

components and composition, and/or method of manufacture of a dug product after

approval, BE may need to be re-demonstrated. For approved first-entry products, the

drug product after the change should be compared to the drug product before change.

For approved interchangeable multi-source products, the drug product after the change

should be compared to the reference listed drug.

2.4.3 Average bioequivalence versus Therapeutic equivalence

Clinical studies comparing pioneer and generic drugs are rarely performed, and studies

comparing one generic product with another are almost never performed. However, in

the 1970s it was recognized that differences in the formulation of products containing

the same amount of active ingredient could result in significant differences in

bioavailability and several cases of therapeutic inequivalence involving generic products

were reported (Kluznik et al. 2001, Weidekamm et al. 1998, Joshi et al. 1990).

Similarly, several more recent reports involving clinical differences or serious

bioequivalence problems with generic products have involved “B”-rated products.

(Campagna 1963, Lander 1971, Alvarez et al. 1981, Lund, 1974, Meyer et al. 1982,

Dubovsky, 1987, Baker et al. 1988; Ansbacher, 2001). However, numerous case

reports have also noted problems temporally related to generic switches for a number

of “A”-rated products. (MacDonald et al. 1987, Wyllie et al. 1987, Hope and Havrda

et al. 2001, Meyer et al. 1992, Welty et al, 1992, Gilman et al. 1993, Reiffel and Kowey

et al. 2000, Wagner and Dent et al. 2000, Rosenbaum et al. 2001, Sajbel et al. 2001,

Kluznik et al. 2001).



In response to such reports of possible therapeutic inequivalence, the FDA established

the Therapeutic Inequivalence Action Coordinating Committee (TIACC) housed

within the FDA Center for Drug Evaluation and Research to identify, evaluate, and

when appropriate, investigate reports of apparent therapeutic inequivalence and take

appropriate corrective action. Since the formation of the TIACC in 1988, the FDA has

investigated more than 60 reports of potential generic product inequivalence but could

not find a single example of therapeutic failure when an FDA-designated therapeutically

equivalent generic product, which was manufactured to meet its approved

specifications, was substituted for the corresponding brand-name drug listed in the

FDA’s Approved Drug Products with Therapeutic Equivalence Evaluations. Moreover

other independent studies have confirmed the bioequivalence and/or therapeutic

equivalence of many other “A”-rated generic products (Francisco et al. 1984, Midha et

al. 1984, Zaman et al. 1986, Eldon et al. 1989, Sharoky et al. 1989, Midha et al. 1990,

Hartley et al. 1991, Meyer et al. 1998).

The perception persists that the current bioequivalence approach for approving generic

products does not adequately account for intra-individual variation in drug

disposition. Pharmacokinetic bioequivalence studies are a surrogate for clinical

outcomes. The critical question is whether assessment of bioequivalence (average)

assures therapeutic equivalence. Concerns have been raised about use of the average

bioequivalence approach to assure interchangeability for multisource products. It has

been suggested that this approach may not be adequate for all drugs and that modified

procedures and additional data may be necessary (Schall and Luus 1993).

Average bioequivalence approach has been indicated to be insufficient to warrant

bioequivalence of the test formulation and the reference formulation, since it compares

the average bioavailability values of the test and the reference formulations and does not

consider differences in variance of test and reference formulation (Nakai et al. 2002).

Measures of average bioequivalence lack any measure of intrasubject variability, and no

such information is provided to physicians in the package inserts. Due to these

concerns raised over the years, on the use of average bioequivalence for evaluation of

comparability between formulations, scientists from academia, industry and regulatory

agencies, propose the use of concepts of individual and population bioequivalence

(Chen et al.2000).



An individual bioequivalence approach has been advocated as a more appropriate

measure to ensure interchangeability (William et al. 2000). Because of the within-

subject focus, individual bioequivalence assessments are usually based on a replicate

study design in which each subject receives both the test and reference products on at

least two occasions. This approach requires a criterion and statistical analysis of within-

individual variance for both test and reference products, and also estimates if two

pharmaceutically equivalent products exhibit a subject-by-formulation interaction.

Presence of a subject-by-formulation interaction means that the difference between

formulations is not the same from subject to subject. The FDA also has proposed

replacing the 1992 average bioequivalence approach with population and individual

bioequivalence (PBE and IBE) (CDER, 1997).

2.4.4 Individual bioequivalence

The IBE criterion encourages BE studies in subjects more representative of the general

population or even in patients for whom the drug is intended, as opposed to healthy

young males where detection of S*F interaction is less likely. This feature addresses a

frequently expressed concern that BE studies in healthy young males lack clinical

relevance. A key concept underlying IBE criterion relates to the term switchability,

which denotes the situation where a patient currently on one formulation switches to

another with the expectation that the safety and efficacy of the drug will remain

essentially unchanged. The criterion uses, in the aggregate, a distance concept that

compares means and variances of T and R products. For individual BE, a subject-by-

formulation (S*F) interaction variance, and within-subject variance for both T and R

products are estimated. By expanding the variance terms, the proposed criterion offers

many consumer and producer advantages, including: (i) assurance of switchability; (ii)

rewards for reduction of variance in the T product; (iii) scaling for highly variable

and/or narrow therapeutic range drugs.

In the IBE criterion, replicate designs are required, in which at least the R, and

commonly both R and T drug products, are each administered on two separate

occasions. The re-test characteristics of replicate study design allow scrutiny of outliers.

IBE can be calculated as:

2D = [(2

BT - 2BR)2 + 2(1-) BT BR



1= [(T - R)2 + 2D + 2

WT - 2WR ]/ 2

WR when WR > 0.2

1= [(T - R)2 + 2D + 2

WT - 2WR ]/ 0.22 when WR < 0.2

Where,

T = mean (test)

R = mean (reference)

2WT = within subject variance (test)

2WR = within subject variance (reference)

2BT = between subject variance (test)

2BR = between subject variance (reference)

Again, 2WR is set to 0.20 (that is, constant scaled versus reference standard) in the

denominator of the formula 1 when the point estimate of the parameter based on the

original data set falls below 0.20 (CDER, 1997).

Individual BE is demonstrated when; 1 (0.95) < 2.45, where p (0.95) is defined as the

95th quartile of 1 based on the non-parametric percentile method using 2000 bootstrap

samples. The bootstrap is used, as the exact distribution for the parameter p has not yet

been derived.

2.4.5 Population bioequivalence

Population bioequivalence approach, which evaluates the total bioavailability variances

in addition to the average bioavailability values, has been proposed as a method to

overcome the disadvantages of average bioequivalence approach (Hauschke and

Steinijans, 2000). FDA has also proposed the use of population bioequivalence as a

bioequivalence study which might guarantee prescribability and which is applicable in

the development stages of novel drugs (CDER, 1997). Based on earlier published

reports of bioequivalence in literature, it was concluded that population bioequivalence

value was affected more extensively by the bioavailability variance rather than by the



average bioavailability (Nakai et al, 2002). PBE criteria aggregate the difference between

the population means and variances.

The key motivation behind the proposed changes in BE criteria lie in answering more

appropriate questions regarding bioequivalence. In the case of pre-marketing approval,

one can formulate the bioequivalence question as “Can a patient begin their therapy

with either formulation (commercial or clinical trial) and be assured of same results in

terms of safety and efficacy” This has been called the concept of prescribability (CDER,

1997) and is linked to PBE criteria. In case of post-marketing changes, the BE question

becomes “Can I safely and effectively switch my patient from their current formulation

to another” This has been called the concept on switchability and is linked to the IBE

criteria. PBE can be calculated as:

p= [(T - R)2 + 2TT - 2

TR]/ 2TR when TR > 0.2

p= [(T - R)2 + 2TT - 2

TR]/ 0.22 when TR < 0.2

Where, T = mean (test)

R = mean (reference)

2TT = total variance (test)

2TR = total variance (reference)

p is calculated in one of the two ways depending on the point estimate for 2TR based on

the original data set. When this estimate falls below 0.20, a constant scaling procedure

is used. Otherwise, the scaling is proportional to 2TR. This has been referred to as

‘constant scaled’ and ‘reference scaled’ respectively (CDER, 1997). Population BE is

demonstrated when; p (0.95) < 1.75, where p (0.95) is defined as the 95th quantile of p

based on the non-parametric percentile method using 2000 bootstrap samples. The

bootstrap is used, as the exact distribution for the parameter p has not yet been derived.

2.4.6 Design and evaluation of bioequivalence study

The preferred approach is an in vivo study carried out in healthy volunteers to whom

the 2 preparations (generic and innovator) are alternatively administered.



The design and evaluation of well controlled bioequivalence studies require the

cooperative input from pharmacokineticists, statisticians, clinicians, bio-analytical

chemists, and others. The design of a bioavailability and/or bioequivalence study is

dependent upon the drug, dosage form and study objectives. For BE studies, both the

test and reference drug formulations contain the pharmaceutical equivalent drug in the

same dose and are given by the same route of administration.

A pilot study in small number of subjects can be carried out before proceeding with a

full BE study. This study can be used to validate analytical methodology, assess

variability, optimize sample collection time intervals or provide any other information.

Non replicate crossover study designs are recommended by FDA for immediate release

and modified release dosage forms (CDER, 2003). However replicate designs can also

be used. The recommended method for analysis to establish bioequivalence is average

bioequivalence. The study should be of crossover designs and suitably randomized as

far as possible. Some of the designs are discussed below-

2.4.6.1 Two-Period Crossover Design

In case of two formulations, an even number of subjects should be randomly divided

into two equal groups. In the first period, each member of one group will receive a

single dose of the test formulation and each member of the other group will receive

standard formulation. After a suitable washout period (generally 5 half lives), in the

second period, each member of the respective groups will receive a dose of an

alternative formulation and the experiment will be repeated.

The design can be depicted as follows:

Volunteer No. Period 1 Period 2

1 A B

2 B A

3 A B

4 A B

5 B A

6 B A



2.4.6.2 Latin Square Design

In case of more than two formulations, a Latin square design should be used. For

example in a bioequivalence study of 3 formulations, a group of volunteers will receive

formulations in the sequence shown below:

VolunteerNo.

Period 1 Period 2 Period 3

1 A B C

2 B C A3 C A B

The next group of 3 volunteers will receive formulations in the same sequence as

shown above.

2.4.6.3 Balance Incomplete Block Design (BIBD)

In case there are more than 3 formulations, the Latin square design will not be ethically

advisable, mainly because each volunteer may require the drawing of too many blood

samples. However, if each volunteer is expected to receive at least two formulations,

then such a study can be carried out using Balanced Incomplete Block Design. As per

this design, if there are four formulations, six possible pairs or formulations can be

chosen from four formulations. Then, the first 6 volunteers will receive these six pairs

of formulations and the next six volunteers will receive the same six pairs in reverse

order. The design is depicted below:

Volunteer No. Period 1 Period 2

1 A B

2 A C

3 A D

4 B C

5 B D

6 C D

7 B A

8 C A

9 D A

10 C B

11 D B

12 D C



The minimum acceptable number of volunteers will be 12.

n> {[]2}/2D2 [t+t]2 + 0.25 t2

Where,

n = no. of volunteers

= Required level of significance (0.05)

= Required power of test (0.80)

2 = Error mean sum of squares from ANOVA (estimated/guess)

D = Minimum difference between the means which if present, ought to be detected

The bioequivalence studies are conducted according to a well-defined protocol.

Some elements of a bio-equivalence protocol are listed in Table 2.5:

2.4.7 STATISTICAL ISSUES IN BIOEQUIVALENCE STUDIES

2.4.7.1 Log transformation before ANOVA

The primary comparison of interest in a bioequivalence study is the ratio of average

parameter data (AUC & Cmax) from the test and reference formulations rather than the

difference between them. Log transformation of the data allows the general linear

statistical model to draw inferences about the ratio of the two averages on the original

scale. Log transformation thus achieves the general comparison based on the ratio

rather than on the difference. Moreover, plasma concentration data, including AUC

and Cmax tend to be skewed and their variances tend to increase with the means. Log

transformation corrects this situation and makes the variances independent of the

mean. Further, the frequency distribution skewed to the left, i.e., those with a log tail to

the right is made symmetrical by log transformation. In case no suitable transformation

is available, the non-parametric method should be used. Tmax values being discrete, data

on Tmax should be analysed using non-parametric methods.

The pharmacokinetic parameters, Cmax, Tmax and AUC should be subjected to a three-

way analysis of variance (3-way ANOVA) in order to test differences due to

formulations, period and subjects.



A more complex ANOVA may be appropriate in some circumstances, e.g. if

treatments are replicated. The standard parametric ANOVA assumes homogeneity of

variances, normality and additivity of independent variables. In order to ensure

homogeneity of variances between treatments, Barttlet’s test or a similar test should be

carried out prior to performing the ANOVA.

2.4.7.2 Two one-sided tests procedures (TOST)

This procedure is also referred to as confidence interval approach. This method is used

to demonstrate if the bioavailability of the drug from the test formulation is too high or

low in comparison to the reference drug product. The 90% confidence limits are

estimated for the sample means. In this test, presently required by the FDA, a 90%

confidence interval about the ratio of means of the two drug products must be within

±20% for measurement of the rate and extent of drug bioavailability. The lower 90% CI

for the ratio of means cannot be less than 0.8, and the upper 90% CI for the ratio of the

means cannot be greater than 1.20. The 90% CI is a function of sample size and study

variability, including inter and intra subject variability (CDER, 2003).

Current DCGI requirements for bio-equivalence approval is that 90% confidence

interval should be within 80-125% for log transformed AUC and 70-143% for log

transformed Cmax provided that the drug is safe otherwise 80-125% will be applicable.

For narrow therapeutic index drugs, the log transformed Cmax should be within 90-111%

and for log transformed AUCs 80-125% is applicable. The T/R ratio should be as close

as possible to 95-105%. Intra subject CV should be as low as possible (<15%). The

bioequivalence criteria followed by various regulatory agencies in the world are

mentioned in the Table 2.4.



Table 2 4: Criteria of bio-equivalence of various regulatory agencies

AgencyLog transformed Parameter

Cmax using 90% CI AUC0-t using 90% CI

USFDA 80-125% of reference 80-125% of reference

DCGI80-125% of reference

70-143% of reference for WTIa

80-125% of reference

90-111% of reference for NTI b

drugs.

CPMP (EU)

80-125% of reference NTI drugs)

75-133% of reference (if clinicallyacceptable)



drugs.

CANADIANFDA (CEC)


70-143% of reference for WTIa

drugs.



drugs.

WTIa –Wide Therapeutic Index

NTI b - Narrow Therapeutic Index

DCGI: Drug Control General of India.

USFDA: United State Food and Drug Administration.

CPMP (EU): The Committee for Proprietary Medicinal Products, European Union.

CEC: Canadian Education Centre.



Table 2.5: Elements of the bioavailability Protocol

S. No. CONTENTS

1 INVESTIGATORS' DECLARATION

2 FACILITIES

2.1 Clinical Services & Clinical Laboratory

2.2. Analytical, Pharmacokinetics & Statistical Services

3 OBJECTIVE

4 PRODUCTS TO BE EVALUATED

4.1 REFERENCE (R)

4.2 TEST (A)

4.3 TEST (B)

5 INTRODUCTION

6 PHARMACOLOGY

6.1 Absorption, Distribution, Metabolism and Excretion

6.2 Adverse Effects

6.3 Dosage

7 STUDY DESIGN

7.1 Summary

7.2 Number of Subjects

7.3 Admissions and Stay

7.4 Fasting/Meals

7.5 Sampling Schedule

7.7 Washout Period

8 RESTRICTIONS

8.1 Medications

8.2 Diet



8.3 Activity

9 SELECTION OF SUBJECTS

9.1 Inclusion Criteria

9.2 Exclusion Criteria

10 SCHEDULE OF ASSESSMENTS

11 STUDY MEDICATION

11.1 Handling, Storage and Accountability Procedures

11.2 Dose

11.3 Assignment to Treatment Sequences

11.4 Assessment of Compliance

12 HAEMODYNAMIC MEASUREMENTS

13 PHARMACOKINETICS

13.1 Blood Sampling

13.2 Analytical Procedures

13.3 Pharmacokinetic Parameters

14 SAFETY

14.1 Clinical Safety Measurements

15 HANDLING OF SAFETY PARAMETERS

15.1 Adverse Events

16 STATISTICAL ANALYSIS

17 DEVIATIONS

18 ETHICAL CONSIDERATION

18.1 Basic Principles

18.2 Institutional Review Board

18.3 Informed Consent

18.4 Withdrawal/Drop-out of Subjects from Study

18.5 Volunteer Compensation



19 TERMINATION OF THE STUDY

20 STUDY DOCUMENTATION

21 QUALITY ASSURANCE AUDIT

22 CONFIDENTIALITY OF DATA

23 ARCHIVES

24 PUBLICATION POLICY

25 REFERENCES

26 LIST OF APPENDICES



2.5 DRUG PROFILE

2.5.1 CHEMISTRY

Olmesartan medoxomil, a prodrug, is hydrolyzed to olmesartan during absorption from

the gastrointestinal tract. Olmesartan is a selective AT1 subtype angiotensin II receptor

antagonist.

Olmesartan medoxomil is described chemically as 2,3-dihydroxy 2- butenyl 4-(1-

hydroxy-1-methylethyl)- 2 - propyl- 1- [p-(o-1H-tetrazol-5-ylphenyl)benzyl] - imidazole 5-

carboxylate, cyclic 2,3-carbonate.

Its empirical formula is C29H30N6O6 and its structural formula is:

2.5.2 DESCRIPTION

Olmesartan medoxomil is a white to light yellowish-white powder or crystalline powder

with a molecular weight of 558.59. It is practically insoluble in water and sparingly

soluble in methanol. It is available for oral use as film-coated tablets containing 10 mg,

20 mg, or 40 mg olmesartan medoxomil.



2.5.3 PHARMACOLOGY

2.5.3.1 Pharmacodynamics

Angiotensin II is formed from angiotensin I in a reaction catalyzed by angiotensin

converting enzyme (ACE, kininase II). Angiotensin II is the principal pressor agent of

the reninangiotensin system, with effects that include vasoconstriction, stimulation of

synthesis and release of aldosterone, cardiac stimulation and renal reabsorption of

sodium. Olmesartan medoxomil is an orally active angiotensin II receptor (type AT1)

antagonist. It has more than a 12,500-fold greater affinity for the AT1 receptor than for

the AT2 receptor. It is expected to block all actions of angiotensin II mediated by the

AT1 receptor, regardless of the source or route of synthesis of angiotensin II. The

selective antagonism of the angiotensin II (AT1) receptors results in increases in plasma

renin levels and angiotensin I and II concentrations, and some decrease in plasma

aldosterone concentrations.

Angiotensin II plays a significant role in the pathophysiology of hypertension via the

type 1 (AT1) receptor.

In hypertension, olmesartan medoxomil causes a dose-dependent, long-lasting

reduction in arterial blood pressure. There has been no evidence of first-dose

hypotension, of tachyphylaxis during long-term treatment, or of rebound hypertension

after cessation of therapy.

Once daily dosing with olmesartan medoxomil provides an effective and smooth

reduction in blood pressure over the 24-hour dose interval. Once daily dosing

produced similar decreases in blood pressure as twice daily dosing at the same total

daily dose.

With continuous treatment, maximum reductions in blood pressure are achieved by 8

weeks after the initiation of therapy, although a substantial proportion of the blood

pressure lowering effect is already observed after 2 weeks of treatment. When used

together with hydrochlorothiazide, the reduction in blood pressure is additive and co

administration is well tolerated.

The effect of olmesartan on mortality and morbidity is not yet known.



2.5.3.2 Pharmacokinetics

Absorption and distribution

Olmesartan medoxomil is a prodrug. It is rapidly converted to the pharmacologically

active metabolite, olmesartan, by esterases in the gut mucosa and in portal blood during

absorption from the gastrointestinal tract.

No intact olmesartan medoxomil or intact side chain medoxomil moiety have been

detected in plasma or excreta. The mean absolute bioavailability of olmesartan from a

tablet formulation was 25.6%.

The mean peak plasma concentration (Cmax) of olmesartan is reached within about 2

hours after oral dosing with olmesartan medoxomil, and olmesartan plasma

concentrations increase approximately linearly with increasing single oral doses up to

about 80 mg.

Food had minimal effect on the bioavailability of olmesartan and therefore olmesartan

medoxomil may be administered with or without food.

No clinically relevant gender–related differences in the pharmacokinetics of olmesartan

have been observed.

Olmesartan is highly bound to plasma protein (99.7%), but the potential for clinically

significant protein binding displacement interactions between olmesartan and other

highly bound co-administered drugs is low (as confirmed by the lack of a clinically

significant interaction between olmesartan medoxomil and warfarin). The binding of

olmesartan to blood cells is negligible. The mean volume of distribution after

intravenous dosing is low (16 – 29 L).

Kun-Yan Li et.al conduct a study in 2010 investigated the relative bioavailability and

fasting pharmacokinetic properties of olmesartan after single doses of a 20-mg test

tablet, a 20-mg test capsule, and a commercially available 20-mg reference tablet in

healthy Chinese male volunteers. The study was conducted to satisfy Chinese State

Food and Drug Administration regulatory requirements for approval of a generic

formulation of olmesartan medoxomil. Blood samples were obtained at baseline and at

0.5, 1, 1.5, 2, 2.5,3,4,6,8,12,24,36, and 48 hours after dosing. The value of Cmax found

for tests and reference formulation were 495.0, 396.0, and 530.0 (ng/ml) respectively.

The value of AUC0-t, AUC0-∞ were 3993, 3567, 3849 and 3091, 2847, 2956 ng.hr/ml



respectively. Results of this study conclude that formulations of olmesartan medoxomil

20-mg capsules and tablets met the regulatory criteria for assuming bioequivalence

Metabolism and elimination

Total plasma clearance was typically 1.3 L/h (CV, 19%) and was relatively slow

compared to hepatic blood flow (ca 90 L/h). Following a single oral dose of 14C

labelled olmesartan medoxomil, 10 - 16% of the administered radioactivity was excreted

in the urine (the vast majority within 24 hours of dose administration) and the

remainder of the recovered radioactivity was excreted in the faeces. Based on the

systemic availability of 25.6%, it can be calculated that absorbed olmesartan is cleared

by both renal excretion (ca 40%) and hepato-biliary excretion (ca 60%). All recovered

radioactivity was identified as olmesartan. No other significant metabolite was detected.

Enterohepatic recycling of olmesartan is minimal. Since a large proportion of

olmesartan is excreted via the biliary route, use in patients with biliary obstruction is

contraindicated.

The terminal elimination half life of olmesartan varied between 10 and 15 hours after

multiple oral dosing. Steady state was reached after the first few doses and no further

accumulation was evident after 14 days of repeated dosing. Renal clearance was

approximately 0.5 – 0.7 L/h and was independent of dose.

2.5.3.3 Pharmacokinetics in special populations

Elderly:

In hypertensive patients, the AUC at steady state was increased by ca 35% in elderly

patients (65 – 75 years old) and by ca 44% in very elderly patients ( 75 years old)

compared with the younger age group. This may be at least in part related to a mean

decrease in renal function in this group of patients.

Renal impairment:

In renally impaired patients, the AUC at steady state increased by 62%, 82% and 179%

in patients with mild, moderate and severe renal impairment, respectively, compared to

healthy controls.

Hepatic impairment:

After single oral administration, olmesartan AUC values were 6% and 65% higher in

mildly and moderately hepatically impaired patients, respectively, than in their



corresponding matched healthy controls. The unbound fraction of olmesartan at 2

hours post-dose in healthy subjects, in patients with mild hepatic impairment and in

patients with moderate hepatic impairment was 0.26%, 0.34% and 0.41%, respectively.

Following repeated dosing in patients with moderate hepatic impairment, olmesartan

mean AUC was again about 65% higher than in matched healthy controls. Olmesartan

mean Cmax values were similar in hepatically-impaired and healthy subjects.

Olmesartan medoxomil has not been evaluated in patients with severe hepatic

impairment.

2.5.4 Market experience

The following adverse reactions have been reported in post-marketing experience.

They are listed by System Organ Class and ranked under headings of frequency using

the following convention: very common ( 1/10); common ( 1/100, <1/10);

uncommon ( 1/1,000, <1/100); rare ( 1/10,000, <1/1,000); very rare (<1/10,000)

including isolated reports.

System Organ Class Very rare

Blood and lymphatic system disorders Thrombocytopenia

Metabolism and nutrition disorders Hyperkalaemia

Nervous system disorders Dizziness, headache

Respiratory, thoracic and mediastinal disorders Cough

Gastrointestinal disorders Abdominal pain, nausea, vomiting

Skin and subcutaneous tissue disorders Pruritus, exanthem, rash

Allergic conditions such as angioneurotic oedema,dermatitis allergic, face oedema and urticaria

Musculoskeletal and connective tissue disorders Muscle cramp, myalgia

Renal and urinary disorders Acute renal failure and renal insufficiency (Seealso under Investigations)

General disorders and administration siteconditions

Asthenic conditions such as asthenia, fatigue,lethargy, malaise

Investigations Abnormal renal function tests such as bloodcreatinine increased and blood urea increased

Increased hepatic enzymes



Single cases of rhabdomyolysis have been reported in temporal association with the

intake of angiotensin II receptor blockers. A causal relationship, however, has not been

established.

2.5.5 Special warnings and precautions for use

Intravascular volume depletion

Symptomatic hypotension, especially after the first dose, may occur in patients who are

volume and/or sodium depleted by vigorous diuretic therapy, dietary salt restriction,

diarrhoea or vomiting. Such conditions should be corrected before the administration

of olmesartan medoxomil.

Other conditions with stimulation of the renin-angiotensin-aldosterone system

In patients whose vascular tone and renal function depend predominantly on the

activity of the renin-angiotensin-aldosterone system (e.g. patients with severe congestive

heart failure or underlying renal disease, including renal artery stenosis), treatment with

other drugs that affect this system has been associated with acute hypotension,

azotaemia, oliguria or, rarely, acute renal failure. The possibility of similar effects

cannot be excluded with angiotensin II receptor antagonists.

Renovascular hypertension

There is an increased risk of severe hypotension and renal insufficiency when patients

with bilateral renal artery stenosis or stenosis of the artery to a single functioning kidney

are treated with medicinal products that affect the renin-angiotensin-aldosterone system.

Renal impairment and kidney transplantation

When olmesartan medoxomil is used in patients with impaired renal function, periodic

monitoring of serum potassium and creatinine levels is recommended. Use of

olmesartan medoxomil is not recommended in patients with severe renal impairment

(creatinine clearance < 20 mL/min).There is no experience of the administration of

olmesartan medoxomil in patients with a recent kidney transplant or in patients with

end-stage renal impairment (i.e. creatinine clearance <12 mL/min).

Hepatic impairment

There is no experience in patients with severe hepatic impairment and therefore use of

olmesartan medoxomil in this patient group is not recommended.



Hyperkalaemia

The use of medicinal products that affect the renin-angiotensin-aldosterone system may

cause hyperkalaemia.

The risk, that may be fatal, is increased in elderly, in patients with renal insufficiency

and in diabetic patients, in patients concomitantly treated with other medicinal products

that may increase potassium levels, and/or in patients with intercurrent events.

Before considering the concomitant use of medicinal products that affect the renin-

angiotensin-aldosterone system, the benefit risk ratio should be evaluated and other

alternatives considered.

The main risk factors for hyperkalaemia to be considered are:

- Diabetes, renal impairment, age (> 70 years)

- Combination with one or more other medicinal products that affect the renin-

angiotensin-aldosterone system and/or potassium supplements. Some medicinal

products or therapeutic class of medicinal products may provoke a hyperkalaemia: salt

substitutes containing potassium, potassium-sparing diuretics, ACE inhibitors,

angiotensin II receptors antagonists, non steroidal anti-inflammatory drugs (including

selective COX-2 inhibitors), heparin, immunosuppressor as ciclosporin or tacrolimus,

trimethoprim

- Intercurrent events, in particular dehydration, acute cardiac decompensation,

metabolic acidosis, worsening of renal function, sudden worsening of the renal

condition (e.g. infectious diseases), cellular lysis (e.g. acute limb ischemia,

rhabdomyolysis, extended trauma).

Close-monitoring of serum potassium in at risk patients is recommended.

Lithium

As with other angiotensin-II receptor antagonists, the combination of lithium and

olmesartan medoxomil is not recommended.

Aortic or mitral valve stenosis; obstructive hypertrophic cardiomyopathy:

As with other vasodilators, special caution is indicated in patients suffering from aortic

or mitral valve stenosis, or obstructive hypertrophic cardiomyopathy.



Primary aldosteronism

Patients with primary aldosteronism generally will not respond to antihypertensive drugs

acting through inhibition of the renin-angiotensin system. Therefore, the use of

olmesartan medoxomil is not recommended in such patients.

Ethnic differences

As with all other angiotensin II antagonists, the blood pressure lowering effect of

olmesartan medoxomil is somewhat less in black patients than in non-black patients,

possibly because of a higher prevalence of low-renin status in the black hypertensive

population.

Pregnancy

Angiotensin II antagonists should not be initiated during pregnancy. Unless continued

angiotensin II antagonists therapy is considered essential, patients planning pregnancy

should be changed to alternative anti-hypertensive treatments which have an established

safety profile for use in pregnancy. When pregnancy is diagnosed, treatment with

angiotensin II antagonists should be stopped immediately and, if appropriate,

alternative therapy should be started.

Others

As with any antihypertensive agent, excessive blood pressure decrease in patients with

ischaemic heart disease or ischaemic cerebrovascular disease could result in a

myocardial infarction or stroke.

This medicinal product contains lactose. Patients with rare hereditary problems of

galactose intolerance, the Lapp-lactase deficiency or glucose-galactose malabsorption

should not take this medicinal product.

2.5.6 Contraindications

Hypersensitivity to the active substance or to any of the excipients.

Second and third trimesters of pregnancy.

Biliary obstruction.

2.5.7 Overdose

Only limited information is available regarding overdosage in humans. The most likely

effect of overdosage is hypotension. In the event of overdosage, the patient should be



carefully monitored and treatment should be symptomatic and supportive. (SPC:

Summary product Characteristics 2009).

2.5.8 Drug Treatment of Hypertension

Treatment with drugs should be started in patients with blood pressures >140/90 mm

Hg in whom lifestyle treatments have not been effective. Different classes of

antihypertensive drugs along their mechanism of action are shown as:

Angiotensin-converting enzyme Inhibitors

These agents reduce blood pressure by blocking the renin-angiotensin system. They do

this by preventing conversion of angiotensin I to the blood pressure raising hormone

angiotensin II. They also increase availability of the vasodilator bradykinin by block-ing

its breakdown. Angiotensin-converting enzyme inhibitors are well tolerated. Their main

side effect is cough (most common in women and in patients of Asian and African

background). Angioedema is uncommon but potentially serious complications that can

threaten airway function, and it occurs most frequently in black patients.

These drugs have established clinical outcome benefits in patients with heart failure,

post–myocardial infarction, left ventricular systolic dysfunction, and diabetic and non

diabetic chronic kidney disease.

Thiazide and Thiazide-like Diuretics

These agents work by increasing excretion of sodium by the kidneys and additionally

may have some vasodilator effects. Clinical outcome benefits (reduction of strokes and

major cardiovascular events) have been best established with chlorthalidone,

indapamide, and hydrochlorothiazide, although evidence for the first two of these

agents has been the strongest. Chlorthalidone has more powerful effects on blood

pressure than hydrochlorothiazide (when the same doses are compared) and has a

longer duration of action.

The main side effects of these drugs are metabolic (hypokalemia, hyperglycemia, and

hyperuricemia). The likelihood of these problems can be reduced by using low doses

(eg, 12.5 mg or 25 mg of hydrochlorothiazide or chlorthalidone) or by combining these

diuretics with angiotensin-converting enzyme inhibitors or angiotensin receptor

blockers, which have been shown to reduce these metabolic changes. Combining

diuretics with potassium-sparing agents



Note: Thiazides plus b-blockers are also an effective combination for reducing blood

pressure, but since both classes can increase blood glucose concentrations this

combination should be used with caution in patients at risk for developing diabetes.

Calcium Channel Blockers

These agents reduce blood pressure by blocking the inward fow of calcium ions

through the L channels of arterial smooth muscle cells. There are two main types of

calcium channel blockers: dihydropyridines, such as amlodipine and nifedipine, which

work by dilating arteries; and nondihydropyridines, such as diltiazem and verapamil,

which dilate arteries somewhat less but also reduce heart rate and contractility.

The main side effect of calcium channel blockers is peripheral edema, which is most

prominent at high doses; this finding can often be attenuated by combining these agents

with angiotensin-converting enzyme inhibitors or angiotensin receptor blockers.

Beta- Blockers

β-blockers reduce cardiac output and also decrease the release of renin from

the kidney.

They have strong clinical outcome benefts in patients with histories of

myocardial infarction and heart failure and are effective in the management of

angina pectoris.

They are less effective in reducing blood pressure in black patients than in

patients of other ethnicities.

β-blockers may not be as effective as the other major drug classes in preventing

stroke or cardiovascular events in hypertensive patients, but they are the drugs

of choice in patients with histories of myocardial infarction or heart failure.

Many of these agents have adverse effects on glucose metabolism and therefore

are not recommended in patients at risk for diabetes, especially in combination

with diuretics. They may also be associated with heart block in susceptible

patients.

The main side effects associated with b-blockers are reduced sexual function,

fatigue, and reduced exercise tolerance.

The combined α and β-blocker, labetalol, is widely used intravenously for

hypertensive emergencies, and is also used orally for treating hypertension in

pregnant and breastfeeding women.



Alpha -Blockers

α-Blockers reduce blood pressure by blocking arterial α-adrenergic receptors

and thus preventing the vasoconstrictor actions of these receptors.

These drugs are less widely used as first-step agents than other classes because

clinical outcome benefits have not been as well established as with other agents.

However, they can be useful in treating resistant hypertension when used in

combination with agents such as diuretics, b-blockers, and angiotensin-

converting enzyme inhibitors.

To be maximally effective, they should usually be combined with a diuretic.

Since a-blockers can have somewhat beneficial effects on blood glucose and

lipid levels, they can potentially neutralize some of the adverse metabolic effects

of diuretics.

The α-blockers are effective in treating benign prostatic hypertrophy, and so can

be a valuable part of hypertension treatment regimens in older men who have

this condition. Weber, et al (ASH/ISH Hypertension Guidelines)

Centrally Acting Agents

These drugs, the most well-known of which are clonidine and a-methyldopa,

work primarily by reducing sympathetic outflow from the central nervous

system.

They are effective in reducing blood pressure in most patient groups.

Bothersome side effects such as drowsiness and dry mouth have reduced their

popularity. Treatment with a clonidine skin patch causes fewer side effects than

the oral agent, but the patch is not always available and can be more costly than

the tablets.

In certain countries, including the United States, α-methyldopa is widely

employed for treating hypertension in pregnancy.

Direct Vasodilators

Because these agents, specifically hydralazine and minoxidil, often cause fluid

retention and tachycardia, they are most effective in reducing blood pressure

when combined with diuretics and β blockers or sympatholytic agents. For this

reason, they are now usually used only as fourth-line or later additions to

treatment regimens.



Hydralazine is the more widely used of these agents. The powerful drug

minoxidil is sometimes used by specialists in patients whose blood pressures are

difficult to control. Fluid retention and tachycardia are frequent problems with

minoxidil, as well as unwanted hair growth (particularly in women). Furosemide

is often required to cope with the fluid retention.

Mineralocorticoid Receptor Antagonists

The best known of these agents is spironolactone. Although it was originally

developed for the treatment of high aldosterone states, it recently has become

part of standard treatment for heart failure.

Eplerenone is a newer and better-tolerated agent, although most experience in

difficult-to-control hypertension has been with spironolactone.

In addition, these agents can be effective in reducing blood pressure when

added to standard 3-drug regimens (angiotensin-converting enzyme inhibitor or

angiotensin receptor blocker/ calcium channel blocker/diuretic) in treatment-

resistant patients. This may be because aldosterone excess can contribute to

resistant hypertension. NICE Clinical Guidelines. February 2011.

Choice of antihypertensive agent in patients with co morbid and associated

conditions is shown in table 2.6( Guide to management of Hypertension 2010).

Table 2.6 Antihypertensive agents in co morbid and associated condition

Condition Potentially beneficialPotentially harmful

Caution Contraindicated

Angina

β-blockers(exceptoxprenolol,pindolol),calcium channel blockers,ACE inhibitors

Atrial fibrillation

Remodelling: ACEinhibitors, angiotensin II

receptor antagonists,Ratecontrol: verapamildiltiazem,beta blockers

Asthma/COPD Cardioselective βblockers(except



β- blocker (e.gatenolo,metoprolol) usecautiously inmild/moderateasthma COPD

cardioselectiveagents)

Bradycardia, 2nd or3rddegree-eatrioventricularblock

Beta-blockers,verapamil,diltiazem

Depression

Beta-blockers,clonidine,

methyldopa,moxonidine

Gout Losartan Thiazidediuretics

Heart failure

ACE inhibitors,angiotensin II receptorantagonists, Thiazide

diuretics, Beta-blockers(bisoprolol, carvidilol,metoprolol controlled

release),spironoloactone

Calcium channelblockers

(especiallyverapamil,diltiazem)

Alpha blockersin aortic stenosis

Beta-blockers inuncontrolledheart failure

Post myocardial

infarction

Beta-blockers (exceptoxprenolol, pindolol),

ACE inhibitors,eplerenone

Pregnancy Atenolol,oxprenolol

ACE inhibitors,angiotensin II

receptorantagonists

Chronic kidneydisease

ACE inhibitors,angiotensin II receptor

antagonists†Tight bilateral

renal arterystenosis (unilateral

in patient withsolitary kidney)

ACE inhibitors,angiotensin II

receptorantagonists

Post stroke

ACE inhibitors,angiotensin II receptorantagonists, low-dosethiazide-like diuretics

Type 1 or type 2diabetes withproteinuria or

microalbuminuria

ACE inhibitors,angiotensin II receptor

antagonists

Beta-blockers,Thiazidediuretics

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