CSDDS

6: DISCUSSION6.1. METHOD DEVELOPMENT AND VALIDATION FOR ANALYSIS OF

DICLOFENAC SODIUM IN TABLETS:

Spectrophotometric method was developed for determination of

diclofenac sodium in tablets with detection at 276 nm. The validation of

method was done with respect to linearity, range, precision and

accuracy. Method established was accurate and precise as % recovery

found close to 100 % and % RSD was less than 2 % which is in the

acceptable range according to the ICH guidelines.

6.2 COMPATIBILITY STUDY OF DRUG AND EXCIPIENTS: The drug

excipients mixtures IR spectra showed the presence of characteristic

drug peaks thus indicating no evidence of the interaction between the

drug and excipients used in the study.

6.3 EVALUATION OF DICLOFENAC SODIUM CORE TABLETS: Core

tablet properties were found complying with various official and

nonofficial evaluation tests for tablet. The breaking force of 5-6 kg /cm2

for the core was deemed to be convenient as HPMC barrier coat was

being provided and further increase would have affected the prompt

disintegration and quick release. The optimum concentration of

superdisintegrant SSG was decided to be 5% as formulation F2 (2.5%

SSG) showed a DT of more than 3 min as compared to F3 (5% SSG)

which showed DT of 30 sec. A further increase in concentration would

not have yielded any significant reduction in DT; on the contrary it would

have swelled and formed the diffusion layer preventing ingress of water

CSDDS

affecting DT adversely. Therefore F3 was selected for further coating

operation.

6.4 PREPARATION AND EVALUATION OF CSDDS BASED ON PH

APPROACH

6.4.1 Barrier Coating: The HPMC coating was applied as a seal coat

between Eudragit FS 30 D aqueous coating and diclofenac Na core tablet

with superdisintegranting agent SSG in order to avoid leaching of

moisture into tablet core. The HPMC 15 cps being hydrophilic did not

interfere with tablet DT (less than 1 min) and also could provide the

effective barrier to the water from Eudragit FS 30D dispersion.

6.2.2 SEM: The average coating thickness of 130, 177 and 253 μm with

coating level of 10%, 15% and 20% (w/w) respectively was observed along

with homogeneous film, this shows that as tablet weight gain increases,

there is an increase in coating thickness.

6.2.3 In vitro release study: In ulcerative colitis, colon is the most

inflamed part 11 and it is required for a dosage form to completely release

the drug at this site at the faster rate. This means that better abatement

of inflammation, release should start at 5thhr corresponding to the

approximate arrival time of dosage form in the ascending colon. These

studies indicate that up to pH 6.8, release is dependent on coating level

but at threshold pH of 7.2 all formulations released the drug significantly

irrespective of coating level. This is due the Eudragit FS 30 D dissolution,

because of ionization of its –COOH groups and immediate disintegration

CSDDS

of core leading to fast dug release. Formulation F1C which had highest

coating level (15% w/w) and contained no superdisintegrant displayed

the lag time of more than 6 hr.

Simultaneously the dependence of lag time in the formulation containing

superdisintegrant SSG was also evident from the lag times of formulation

F3A, F3B, F3C and F3D (Table 5.4). This increased in lag time is

attributed to diffusion path length and tortuosity of the coat at more

coating levels 32.

The coating levels beyond 15 % w/w were not preferred as it did not offer

significant increase in lag time as compare to 10% w/w coating level with

the obvious advantages of low coating levels, reduced processing time

and lower weight. Also the lag time with 20% w/w coating level was

higher (more than 7 hr) which corresponds to the descending colon

where negligible absorption of drug would occur.

F1B and F3B both with same coating level (10% w/w), show different lag

times, due to presence of superdisintegrant SSG in F3B. This is

explained by the phenomenon of pH dependent dissolution of Eudragit

FS30D coat and subsequent fast disintegration as described above, this

is evident as T90% for both the formulations is same 3.

From in vitro study results it can be concluded that superdisintegrant

SSG plays an important role to achieve proper lag time of 5hr

corresponding to ascending colon and ensure a higher amount of drug

release immediately after lag time. Achieving the higher concentration of

CSDDS

diclofenac sodium in the colon may be beneficial to produce local anti-

inflammatory effect, since this area is the most inflamed in ulcerative

colitis.

6.2.4 In vivo X-ray results: Results of in vivo studies were in agreement

with the results of in vitro dissolution studies, that is formulation F3B

having superdisintegrant SSG and coating level of 10% w/w showed

similar lag time of 5 hr (average time to reach colon) and instant drug

release both in vitro and in vivo. Though polymer Eudragit FS 30 D

solubility is pH dependent, which solubilize at the slightly alkaline

medium, the percentage coating level also had significant role on the site

of release. The increase in coating level increases time required for

diffusion of intestinal fluid and erosion of the tablet coat. This reinforces

the crucial role of superdisintegrant in achieving site specific release in

ascending colon and ability to unload the drug content promptly.

6.4 COMPARISON OF EUDRAGIT FS30D AND EUDRAGIT S100 AS

COATING POLYMER FOR CSDDS

6.4.1 In vitro drug release study: During drug release study by

continuous pH change method the Eudragit S100 and Eudragit FS30D

coated formulations displayed similar lag time corresponding to pH 6.8

but Eudragit S 100 formulation displayed faster drug release at pH 7.2

(fig 5.8).

This is explained by the fact that Eudragit FS 30D contains higher ratio

of ester to carboxylic groups than Eudragit S100 113, 114 which gets

CSDDS

dissolved in controlled manner at pH 6.8-7.2 32, 89, 96, whereas Eudragit

S100 contains higher ratio of carboxylic to ester group which get

hydrolyzed only at higher pH.

A separate drug release study (fig 5.9) at pH 6.8 and 7.2 buffer following

incubation at pH 1.2 buffer for 2 hrs, indicated the superiority of

Eudragit FS30D in inflammatory conditions where pH of colon is low107

(about 6.8).

In the drug release study at pH 6.8 the extended lag time displayed by

Eudragit S 100 coated formulations and subsequent low release is

attributable to its inability to hydrolyze at low pH values.

Whereas in release study at pH 7.2 due to favorable pH for hydrolysis

both polymer underwent hydrolysis rapidly leading to small lag time of

less than 2hr and subsequent fast release.

The threshold pH of EudragitFS30D is 6.8 and 7.2 compared to that of

Eudragit S100 which lies above 7.032,96, these results are conformity

with the work of Huyghebaert et al54 and ChunshengGao et al 90

For effective treatment of ulcerative colitis drug release should start from

terminal part of ileocecal region or from the cecum, The outcome of study

proves the superiority of Eudragit FS30D over Eudragit S100 in

developing formulation for targeted release to ascending colon in IBD

where pH is reported to be lower than usual107. As tablets reach the

initial segment of colon, ability of Eudragit FS30D to dissolve, ensures

CSDDS

the availability of drug in disperse or dissolved form in all further parts of

colon to produce effective local as well as systemic effect.

6.3.2 In vivo studies: In vivoroentographic study revealed that both

Eudragit S100 coated tablet (10%w/w) and Eudragit FS30D coated tablet

disintegrated in the cecum this reinforces the claim that

superdisintegrant SSG helps in disintegration of tablet irrespective of pH

threshold of polymer at same coating level. The disintegration of both

tablets in cecum, is not in agreement with results of invitro release

studies which indicate that Eudragit FS30D coated tablet begin release

at 6.8 pH after appropriate lag time as compare to Eudragit S100 which

release specifically at higher pH this is because the study was carried out

in healthy volunteers where pH of cecum was 6.8- 7.2 in all the cases.

6.4 PREPARATION AND EVALUATION OF CSDDS BASED ON

BACTERIAL APPROACH

6.4.1 Full Factorial Design: Results of full factorial design formulation

indicate that increase in concentration of amylose did not contribute

significantly to drug release in 5hr (which corresponds to time

requirement for passage to colon), whereas increase in HPMC K100LV

decreased the drug release in 5 hr which can be attributed to swelling of

polymer causing gel formation and preventing the drug release.

(Fig.5.12). HPMC K100LV appreciably decreased t 90% whereas amylose

marginally decreased t90%. (Fig.5.13). Both the parameters were reduced

due interaction of factors. In order to validate the equations, three

CSDDS

optimum formulations were selected from grid search done over the

complete experimental area. The criteria for selection of optimum were

primarily based on the lag time (5 hr) and T90% (minimum time).

Formulations corresponding to this optimum were prepared and

evaluated for lag time and t90%. The r2= 0.9954 indicated predicted and

observed values are in good agreement. The observed and predicted

responses obtained by using factorial design along with the residual

errors for these three optimum formulations are shown in table 5.13.

Low magnitude of error designate high prognostic ability of response

surface, since the response variables predicted error ranged

between0.057 to 0.097. Analysis of variance (ANOVA) indicates that the

assumed regression models were significant and valid for each

considered response

6.4.2 In vitro drug release studies

6.4.2.1 Coating polymer ratio effect

The release profiles for compression coated diclofenac sodium tablets

prepared shows no release up to 5hr and tablets were intact this is

attributed to the coat which formed a swollen gel which does not allow

diffusion of drug through the core tablet till 5hr and lag time was found

to increase with increase in HPMC and amylose polymer concentration.

The drug was released from the formulation after 5h in presence of

enzyme at pH 6.8(stage II). Enzymatic degradation of amylose collapse

polymer back bone leading to a reduction in their molecular strength and

CSDDS

the formulation was unable to hold the drug entity any longer. The high

rate of drug release for formulation R4 and R7containing low level of

HPMCin these formulations was attributed to thin gel and rapid ingress

of water leading to more rapid dissolution of swollen amylose by α-

amylase enzymes which create perforations for fluid diffusion through gel

layer and subsequent swelling of sodium starch glycolate to disintegrate

the tablet. Slow drug release was observed for formulations R2, R3 and

R6, which was due to higher HPMC concentration leading to the

formation of thick gel layer, resisting the tablet to disintegrate and

release the drug.

6.4.2.2 Effect of coating composition.

Slow drug release from tablets coated only with HPMC K100LV (without

amylose) (B2) is due to gel formed around the tablet due to HPMC

K100LV which does not allow the pore formation and penetration of fluid

enough to cause tablet disintegration. This shows that the site specificity

of release is based on biodegradation of amylose and HPMC helps in film

formation along with amylose.

6.4.2.3 Effect media pH on drug targeting

The results suggested that pH has no effect on dissolution behavior of

the optimized formulations; since HPMC is pH independent polymer and

amylose also remains unaffected by pH, the compressed tablet is capable

to release the drug particularly in the colon irrespective of change in pH,

CSDDS

this ability is very useful as the colon pH is found to be lowered in

conditions such as IBD11, 115.

6.4.2.4 Effect of superdisintegrant on drug targeting

Fastest drug release for tablets containing sodium starch glycolate (F1),

as compared to the tablet containing no superdisintegrant (F2) is by

virtue of the presence of superdisintegrant sodium starch glycolate which

has rapid swelling action even in presence of minimal fluid that causes

bursting effect after penetration of water into the tablets. However, core

tablet without superdisintegrant, did not expand enough to burst the

tablet and the gel formed due to HPMC delayed the drug release (Fig.

5.17). This effect was further confirmed by in vivo study in human

volunteer (Fig. 5.18).

6.4.3 In vivo X-ray results

From the abdominal radiographs, taken at different points of time, it was

seen in presence of variation in gastric transit time, formulation with

superdisintegrant coated with amylose and HPMC (A3) disintegrated at

cecum or ileocecal region which is initial segment of colon. This

disintegration is due to degradation of amylose coat by amylase enzyme

present in coloic region, secreted by bifidobacteria and subsequent

bursting effect of superdisintegrant, whereas tablet without

superdisintegrant with same coating composition of 285:150 of amylose

and HPMC respectively remained intact in the ascending colon after 6h.

CSDDS

These results are in agreement with in vitro release studies, which show

drug release after the addition of amylase enzyme.

6.5 PREPARATION AND EVALUATION OF CSDDS BASED ONTIME

DEPENDENT APPROACH

6.5.1 Evaluation of diclofenac sodium core tablets

Core tablets satisfied the official and unofficial quality requirements, the

tablet had sufficient mechanical strength and drug content.

6.5.2 In vitro release study

The tablet coated with HPMC displayed complete drug release in less

than 2h during drug release study by continuous pH change due to

erosion of low viscosity grade HPMC and hence was deemed unsuitable

for colon targeting. The tablet coated with Eudragit RSPO could resist the

release till 5 hr and complete drug release occurred after 5hr (lag time)

within 60 min. The Eudragit RSPO being a swellable hydrophilic polymer

is accountable for a lag phase prior the onset of release. The hydrophilic

polymer undergoes a glassy-rubbery transition in aqueous fluids and, it

becomes more permeable, dissolves and/or erodes in the rubbery state.

This mechanisms is responsible for lag time in colonic drug delivery by

time dependent, hence release starts after 5hr. Here too the

incorporation of superdisintegrant SSG in tablet core could accomplish

fast unloading of the drug by virtue of disintegration due to swelling as

soon as penetration of water through the pores generated by polymer

CSDDS

erosion. This provides higher concentration at the site of inflammation

for local and systemic effect at the initial segment of colon. The lag time

and time required to complete release increased with increase in coating

level, this is attributed to increased diffusion path length with increased

thickness and subsequent delay in erosion of polymer. The high lag time

(>5hr) and less than 10% drug release after 7hr will lead the formulation

to bypass the colonic region without releasing the significant amount of

drug. Thus the utility of incorporating the superdisintegrant got again

highlighted even in this approach to colon specific drug delivery system.

6.5.3 In vivo X-ray results

Results of in vivo studies are in agreement with in vitro dissolution

results. The optimized formulation having superdisintegrant SSG and

5% w/w coating level showed similar lag time and instant disintegration

after 6 hr both in vivo and in vitro, this corresponds to time for tablet

reaching colonic region. This shows the pH independent nature of

Eudragit RSPO which dissolved after 5hr corresponding to the colonic

region and inclusion of superdisintegrant helped to achieve instant

disintegration and possible release in initial segment of colon. The tablet

without superdisintegrant does not disintegrate in colon up to ascending

colon.