Drug evaluation

Evaluation means confirmation of identity and determination of quality and

purity of the herbal drug. Evaluation of crude drug is necessary because of three

main reasons: 1- biochemical variations in the drug, deterioration due to treatment

and storage, substitution and adulteration as a result of carelessness, ignorance or

fraud or variability caused by differences in growth, 2- geographical location, 3- time

of harvesting. For the quality control of a traditional medicine, the traditional

methods are procured and studied, and documents and the traditional information

about the identity and quality assessment are interpreted in terms of modern

assessment or monograph in herbal pharmacopoeia . The crude drug can be

evaluated or identified by five methods:

morphological evaluation

It means evaluation of drug by the organs of sense (skin, eye, tongue, nose and

ear) or macroscopic evaluation and it includes evaluation of drugs by color, odor,

taste, size, shape and special feature, like touch, texture etc. it is the technique of

qualitative evaluation based on the study of morphological and sensory profile of

whole drugs. eg. The fractured surfaces in cinchona, quillia and cascara barks and are

important characteristics. Aromatic odour of umbelliferous fruits and sweet taste of

liquorice are the examples of this type of evaluation where odor of drug depends

upon the type and quality of odorous principles (volatile oils) present. Shape of drug

may be cylindrical (sarsapilla), subcylindrical (podophyllum), conical (aconite),

fusiform (jalap) etc, size represent length, breadth, thickness, diameter etc. color

means external color which varies from white to brownish black are important

diagnostic characters. The general appearance (external marking) of the weight of a

crude drug often indicates whether it is likely to comply with prescribed standard

like furrows (alternate depression or valleys), wrinkles (fine delicate furrows),

annulations (transverse rings), fissures (splits), nodules (rounded outgrowth), scars

(spot left after fall of leaves, stems or roots). Taste is specific type of sensation felt by

epithelial layer of tongue. It may be acidic (sour), saline (salt like), saccharin

(sweetish), bitter or tasteless (possessing no taste).

cinchona

cascara bark

2 -Microscopic evaluation

It involves detailed examination of the drug and it can be used to identify the

organized drugs by their known histological characters. It is mostly used for

qualitative evaluation of organized crude drugs in entire and powder forms with help

of microscope.

Using microscope detecting various cellular tissues, trichomes, stomata, starch

granules, calcium oxalate crystals and aleurone grains are some of important

parameters which play important role in identification of certain crude drug. Crude

drug can also be identified microscopically by cutting the thin TS (transverse section),

LS (Longitudinal section) especially in case of wood and by staining them with proper

staining reagents e.g. starch and hemicelluloses is identified by blue color with iodine

solution, all lignified tissue give pink stain with phloroglucinol and HCl etc. mucilage

is stained pink with ruthenium red can be used to distinguish cellular structure.

Microscopic evaluation also includes study of constituents in the powdered drug by

the use of chemical reagents. Quantitative aspects of microscopy includes study of

stomatal number and index, palisade ratio, vein-islet number, size of starch grains,

length of fibers etc which play important role .

Chemical evaluation

Most of drugs have definite chemical constituents to which their biological or

pharmacological activity is attributed. Qualitative chemical test are used to identify

certain drug or to test their purity. The isolation, purification, identification of active

constituents is based on chemical methods of evaluation. Qualitative chemical test

such as acid value, saponification value etc. Some of these are useful in evaluation of

resins (acid value, sulphated ash), balsams (acid value, saponification value and

bester values), volatile oils (acetyl and ester values) and gums (methoxy

determination and volatile acidity). Preliminary phytochemical screening is a part of

chemical evaluation. These qualitative chemical tests are useful in identification of

chemical constituents and detection of adulteration.

Physical evaluation

Physical constants are sometimes taken into consideration to evaluate certain drugs.

These include moisture content, specific gravity, optical rotation, refractive, melting

point, viscosity and solubility in different solvents. All these physical properties are

useful in identification and detection of constituents present in plant .

Biological evaluation

Some drugs have specific biological and pharmacological activity which is utilized for

their evaluation. Actually this activity is due to specific type of constituents present

in the plant extract. For evaluation the experiments were carried out on both intact

and isolated organs of living animals. With the help of bioassays (testing the drugs on

living animals), strength of drug in its preparation can also be evaluated . Some

important biological evaluations are as follow :

1 Antibiotic activity

Some bacteria such as Salmonella typhi, styphylococcus aureus and E. coli are used

to determine the antiseptic value (the degree of antiseptic activity e.g. phenol

coefficient of certain drugs). The activity of antibiotics is also determined by using

Klebsiella pneumonia, Micrococcus flavus, Sarcira lutea etc. Microbiological assays by

cylinder plate method and turbidimetric method are used in evaluation .

2 Hypoglycemic activity

Rabbits, rats or mice are used to test hypoglycemic activity of plant extract. Radio-

immuno assay (RIA) or Enzyme linked immunosorbate assay (ELISA) ameasurement

of insulin levels .

3 Neuropharmacological activity

Testing the herbal drugs with effects on central and autonomic nervous system. CNS

acting drugs like cocaine (Erythroxylum coca), morphine (Papaver somniferum),

cannabinol (Cannabis sativa) are tested using rodents. For testing the herbal drugs

for their effects on ANS guinea pig for antispasmodic activity, rabbit jejunum for

adrenergic activity, rat phrenic-nerve-diaphragm for muscle relaxant activity, frog

rectus for skeletal muscles activity.

spectroscopic method :

Spectroscopy: is the study of the interaction between matter and

electromagnetic radiation. a wide range of spectroscopic techniques are used for

evaluation of crude drug constituents which should be obtained in a pure form.

The electromagnetic radiation utilized in spectroscopic analysis can be divided

according to wavelength, into:

the ultraviolet, its wavelength is ( 185-380 nm).

the visible( 380-780 nm),

The near-infrared (780 - 3000 nm) and

the infrared (3 – 40 µm).

so the spectroscopic analysis depend on the capacity of certain molecules to absorb

vibrations at specific wave lengths.

So if UV light or IR light pass through a sample of organic compound some of light

will be absorbed at specific wave length by the sample, while some of the light will

pass without being absorbed.

Light source photoelectric cells recorder UV or IR (detector)

sample

Each substance give certain absorption spectrum.

The absorption spectrum plot absorption versus or against wave length.

Such absorption spectra are used for identification and determination of structre,

purity and analysis of compounds.

General separation and isolation techniques

1 -Extraction: The choice of extraction procedure depends on the nature of the plant

material and the components to be isolated. Dried materials are usually powdered

before extraction, whereas fresh plants (leaves. etc ) can be homogenized or

UVIR

macerated with a solvent such as alcohol, The latter is also particularly useful for

stabilizing fresh leaves by dropping them into the boiling solvent. Alcohol is a general

solvent for many plant constituents (most fixed oils excepted) and as such may give

problems in the subsequent elimination of pigments, resins, etc. Water immiscible

solvents are widely used ;

light petroleum for (essential and fixed oils, steroids) .

ether and chloroform for (alkaloids, quinones).

The extraction of organic bases ( e.g. alkaloids) usually necessitate

basification of the plant material and a water-immiscible solvent is to be

used ,

for aromatic acids and phenols acidification may be required.

Extraction itself may be performed by repeated maceration with agitation,

percolation or by continuous extraction ( e.g. in a Soxhlet extractor) .

Simple methods of extraction

These are methods used for preparation of certain pharmaceutical products or

liquids called Galenical preparation from Galen Geek physician and these

preparations include: tincture, fluid extract and infusion.

The extract obtained by these methods are not standard and among these methods

are:

1 -Maceration: In this process, the whole or powdered crude drug is placed in a

stoppered container with the solvent and allowed to stand at room temperature for

a period of at least 3 days with frequent agitation until the soluble matter has

dissolved. The mixture then is strained , solidرطب the marc( the dampيصفى

material )is pressed , يعصرand the combined liquids are clarified by filtration or

decantation after standing.

2 -Decoction : بالغلي الاستخلاص

In this process, the crude drug is boiled in a specified volume of water for a defined

time; it is then cooled and strained or filtered. This procedure is suitable for

extracting water-soluble, heat-stable constituents.

3 -Digestion: it’s a method of maceration with continuous heating at 40-60 C to

increase the solubility of active constituents and clarified by filteration.

4 -Infusion: Fresh infusions are prepared by macerating the crude drug for a short

period of time with cold or boiling water. These are dilute solutions of the readily

soluble constituents of crude drugs.

5 -Percolation : بالتقطير الاستخلاص

This is the procedure used most frequently to extract active ingredients in the

preparation of tinctures and fluid extracts. A percolator (a narrow, cone-shaped

vessel open at both ends) is generally used. The solid ingredients are moistened with

an appropriate amount of the specified solvent and allowed to stand for

approximately 4 h in a well closed container, after which the mass is packed and the

top of the percolator is closed. Additional solvent is added as required, until the

percolate measures about three-quarters of the required volume of the finished

product. The Additional solvent is added to form a shallow layer above the mass, and

the mixture is allowed to macerate in the closed percolator for 24 h. The outlet of

the percolator then is opened and the liquid contained therein is allowed to drip

slowly. marc is then pressed and the expressed liquid is added to the percolate.

Sufficient solvent is added to produce the required volume, and the mixed liquid is

clarified by filtration or by standing followed by decanting. سكب

Percolator

Continuous liquid-solid extraction:

Using hot solvent. These methods include more advanced and complicated methods.

A) Soxhlet extraction :

In this method, the crude drug is placed in a porous bag or “thimble” made of strong

filter paper, which is placed in chamber E of the Soxhlet apparatus. The extracting

solvent in flask A is heated, and its vapors condense in condenser D. The condensed

solvent drips into the thimble containing the crude drug, and extracts it by contact.

When the level of liquid in chamber E rises to the top of siphon tube C, the liquid

contents of chamber E flow into flask A. This process is continuous. The advantage of

this method, compared to previously described methods, is that large amounts of

drug can be extracted with a much smaller quantity of solvent .

D

C

E

B

A

B) Ordinary reflux extraction method

This method is less active than Soxhlet extraction method, because the solvent is in

direct contact with the drug to be extracted, so after a period of time the solvent will

be saturated with active constituents, so must remove the solvent and added

another one so there is loss of time and solvent.

C) Distillation:

1 -by steam distillation.

2 -by fraction distillation.

Steam distillation: it's used for volatile oil from crude drug with steam by using

instrument called Clevenger.

Due to influence of hot water, volatile oil extracted from crude drug then vapor of

water and oil will pass through condenser then distillated into receiving tube in

which oil separate from distillated water.

2 -Fractional distillation:

Separation of a mixture of constituents as volatile oil according to their boiling

points.