INTRODUCTION:

Dosage forms that deliver drugs into the colon rather than upper GIT have number of advantages. Oral delivery of drugs to the colon is valuable in the treatment of diseases of colon such as ulcerative colitis, Crohn's disease, colon cancer and infections whereby high local concentration can be achieved while minimizing side effects that occur because of release of drugs in the upper GIT or unnecessary systemic absorption. Ketoprofen, a nonsteroidal anti-inflammatory drug with short biological half life and plasma elimination half life, was selected as a model drug for this study. Ketoprofen possess high permeability and exhibits pH dependent solubility, i.e. it has more solubility in neutral and basic pH as compared to acidic pH ^[1].

Usual dose of Ketoprofen recommended for mild to moderate pain and dysmenorrhoea is 25-50 mg every 6 to 8 hrs. Doses larger than 25 mg generally could not be shown to be significantly more effective but there is a tendency toward faster onset and greater duration of action with 50 mg.

Study by Rao et al provides evidence that Ketoprofen is having significant potency as inhibitor of carcinogenesis and COX-2 derived PGE₂ which is involved in cancer progression ^[2]. As pharmacology of Ketoprofen suggests that it competitively inhibits both cyclooxygenase (COX) isoenzymes, COX-1 and COX-2, by blocking arachidonate binding resulting in analgesic, antipyretic, and anti-inflammatory pharmacologic effects, COX-2 appears to be only constitutively expressed in the brain, kidney, bones, reproductive organs, and some neoplasm (e.g. colon and prostate cancers). As Ketoprofen is NSAIDS drug, it also exhibits the gastric side effect like nausea, vomiting, gastritis etc due to systemic delivery of Ketoprofen. The drug targeting to the colonic region delays the release of the drug or minimizes the release in stomach and small intestine and increases release in the colon for local action, hence reduce the GI side effects which occur due to the drug release in stomach and small intestine.

Out of various approaches available in achieving colon specific drug delivery, use of carriers those are degraded exclusively by colonic bacteria are found promising in providing colon-specific drug delivery ^{[3][4][5][6][7]}. The polysaccharides used as carriers for colon-specific drug delivery include guar gum, locust bean gum, karaya gum, chitosan, amylose, pectin etc^[3][7].

Fig.1 Release profile of guar gum Matrix tablets of Ketoprofen

F1 Drug: Guar gum ratio 1:0.25, F2 Drug: Guar gum ratio 1:0.5,

F3 Drug: Guar gum ratio 1:1.

Fig.2 Release profile locust bean gum matrix tablets of Ketoprofen.

F4 Drug: Locust bean gum ratio 1:0.25, F5 Drug: Locust bean gum ratio 1:0.5. F6 Drug: Locust bean gum ratio 1:1

Various studies revealed the use of guar gum as a carrier for colonic drug delivery in the form of matrix tablet or as a compression coat ^{[8] [9]}. Guar gum is a naturally occurring non ionic polysaccharide derived from seeds of Cyamopsis tetragonolobus (Family: Leguminaciae). It consists of linear chains of (1→4) β D-mannopyranosyl units with α D galactopyranosyl units attached by (1→6) linkages. Locust bean gum has also been used along with chitosan as a carrier for colonic drug delivery^[10]. Locust bean gum is a galactomannan similar to guar gum, extracted from the seed (kernels) of the carob tree (Ceratonia siliqua) and consisting of a (14)-linked β-D-mannopyranose backbone with branch points from their 6-positions linked to α-D-galactose (i.e. 16-linked α-D-galactopyranosyl). So it was thought that both the gums could be used as carrier in the matrix tablet as well as applied as a coat to target Ketoprofen to colon.

The aim of present study is development and evaluation of colon targeted drug delivery system for Ketoprofen using these natural polymers which gives minimal release up to 5 h of dissolution study i.e. in physiological environment of stomach and small intestine and releases most of the drug in colonic regions for local action.

Table No.1:- Composition of Ketoprofen matrix tablets

Code	Drug (mg)	Polymers				Dicalcium Phosphate (mg)
		Guar gum (mg)		Locust bean gum (mg)
F1	50		12.5		--		55.5
F2	50		25		--		43
F3	50		50		--		18
F4	50		--		12.5		55.5
F5	50		--		25		43
F6	50		--		50		18

Total tablet weight: 120 mg; Magnesium stearate and Talc 1 mg each per tablet.

Table No.2:- Composition of core tablets of Ketoprofen

Drug

(mg)

Dicalcium Phosphate (mg)

Magnesium Stearate (mg)

Talc

(mg)

Ac-di-sol

(mg)

64.5

3.5

Total tablet weight: 120 mg

Table No.3:- Composition of compression coated tablets of Ketoprofen

Code Plain core tablet (mg)		Gum coat mixture blends (mg )*		Total Weight [mg]
Code Plain core tablet (mg)		Guar gum	Locust bean gum	Total Weight [mg]
F7	120	200	---	320
F8	120	300	---	420
F9	120	400	---	520
F10	120	---	200	320
F11	120	---	300	420
F12	120	---	400	520
F13*	120	300	---	420
F14*	120	---	300	420

*Tablet formulations with 3% crosscarmellose sodium in core.

Table No.4: Composition of gum coat mixture blends (mg)

Code	Coat weight	Guar Gum	Locust bean gum	DCP	Mg.St.	Talc
G1	200	160	---	35	2	3
G2	300	255	---	40	2	3
G3	400	340	---	55	2	3
G4	200	---	160	35	2	3
G5	300	---	255	40	2	3
G6	400	--	340	55	2	3

DCP-Dicalcium Phosphate; Mg.St.-Magnesium stearate

Table No.5: The characteristics values of the kinetic model for water uptake data

Formulation	Kinetic constant (k)	Swelling exponent (n)	Correlation Coefficient (r²)
F3	2.4227	0.6925	0.8682
F6	1.4801	0.7612	0.8901
F13	22.4750	0.4380	0.9923
F14	23.8946	0.3839	0.9860

MATERIALS AND METHODS:

Ketoprofen (99-100.5% purity) was purchased from BEC Chemical Pvt. Ltd., Mumbai. India. Guar gum (Viscosity of 1 % aqueous dispersion is 3000 cps at 25 ⁰C) and locust bean gum (Viscosity of 1 % aqueous dispersion is 200 cps at 25 ⁰C) were gift sample from Lucid colloids Ltd. Mumbai. Dicalcium phosphate, talc, magnesium stearate and croscarmellose sodium (Ac-Di-Sol) were of USP/ NF grade.

Preparation of Ketoprofen matrix tablets:

Matrix tablets of Ketoprofen were prepared by direct compression method using different proportions of guar gum and locust bean gum as carrier, dicalcium phosphate as diluent, talc and magnesium stearate as lubricant. The composition of different matrix formulations is shown in Table No.1. The matrix tablets were prepared by thoroughly mixing presieved (Sieve # 40) drug, gums, dicalcium phosphate, magnesium stearate and talc. The powder blends were compressed at a compression force of 4000-5000 kg using 6 mm concave punches on Mini press II compression machine (Karnavati Engineering, Ahmedabad). The matrix tablets were tested for hardness, % drug content and In vitro dissolution studies.

Preparation of Ketoprofen compression coated tablets using gum coat:

The core tablets (total weight 120 mg) of Ketoprofen, for compression coating with guar gum and locust bean gum were prepared by direct compression technique. The composition of the core tablets is given in Table No.2. The drug, dicalcium phosphate, magnesium stearate and talc were thoroughly mixed. The uniformity of mixing was assessed by analyzing the samples of the powder mix. The mixture was compressed into core tablets at an applied force of 2000-3000 kg using 6 mm concave punches on Minipress II compression machine (Karnavati Engineering, Ahmadabad). To get the fast release of drug, tablets were also prepared using 3 % Croscarmellose sodium (Ac-Di-sol) in core tablets. The core tablets were tested for hardness, % drug content and In vitro dissolution studies. After confirming the compliance with these tests, the core tablets were compression coated with different amount of coat formulations G1 TO G6 containing 160, 255, 340 mg of gum. The composition of compression coated tablets of Ketoprofen using gums is given in Table No.3. Since gums alone gave very soft coat and did not provide sufficient integrity, diluents were included in the coat formulation to impart enough hardness. The composition of gum coat mixture is given in Table no.4. About one third quantity of the coat was placed in the die cavity (diameter 10 mm), the Ketoprofen core tablets was carefully positioned in the center of the die cavity and was filled with the remainder of the coat. It was then compressed around the core tablets at an applied force of 5000-6000 kg using 10 mm concave punches as described above. All the formulations were tested for their weight variation, friability, hardness, drug content and In vitro drug release characteristics. The hardness of the matrix tablets was determined by using Monsanto Hardness Tester.

Determination of % drug content:

Ten tablets of the each of the formulations were finely powdered. The powder equivalent to the average weight was weighed. It was shaken for the 10 min with 150 ml of methanol, mixed and diluted to 250 ml with methanol. This solution was allowed to stand and 5 ml of supernant liquid was diluted with 100 ml methanol and analyzed for Ketoprofen content at 254 nm by UV visible spectrophotometer.

In vitro drug release studies:

The ability of Ketoprofen tablets to remain intact in the physiological environment of stomach and small intestine was assayed by conducting drug release studies under conditions mimicking mouth to colon transit. In vitro drug release studies of Ketoprofen tablets were carried out in USP (23) dissolution apparatus (Apparatus I, 100 rpm, 37 ± 0.5 ⁰C) for first 2 h in 900 ml of 0.1N HCl, then the dissolution medium was replaced with 6.8 pH Phosphate buffer and tested for drug release up to next 3h and finally continued in pH 7.4 Phosphate buffer. At the end of the time periods 10 ml of sample was taken from each dissolution flask, filtered with Whatmann filter paper, Samples were suitably diluted using dissolution medium and analyzed for Ketoprofen at 259 nm for 0.1N HCL, at 260 nm for 6.8 pH Phosphate and pH 7.4 Phosphate buffer using a UV visible double beam spectrophotometer (Model-UV1701, Shimadzu, Japan).

The ability of the selected press coated tablets containing natural polymers as core material and as compression coat, to the enzymatic action of colonic bacteria were assessed by performing drug release studies in medium containing rat caecal content. The drug release studies were carried out in USP (XXIII) dissolution test apparatus (apparatus 1,100 rpm, 37⁰C) with slight modification. A beaker (capacity 150 ml, internal diameter 55 mm) containing 100 ml of dissolution medium with rat caecal content was immersed in the water contained in the 1000 ml vessel, which was, in turn, immersed in the water bath of the apparatus. The swollen formulation after completing the dissolution studies in 0.1 N HCL (2hr) and pH 6.8 phosphate buffer (3 hr) were placed in the baskets of the apparatus and immersed in the rat caecal content medium and dissolution was continued. The experiment was carried out with continuous CO₂supply into the beaker to simulate anaerobic environment of the caecum and 1 ml samples were taken at different time intervals, filtered and replaced with 1ml of fresh phosphate buffer bubbled with CO₂. The volume was made up to 10 ml with phosphate buffer, for dilution of the sample and samples were analyzed for Ketoprofen content at 260 nm.

Polymer swelling / water uptake studies:

The rate of test medium uptake by the polymer was determined by equilibrium weight gain method. The study was carried out in the USP / NF dissolution apparatus 1. The weight of the tablets and dissolution basket weight were noted. The tablets were placed in the dissolution baskets, immersed in dissolution media maintaining temperature at 37 ±0.5⁰C. At regular intervals, the baskets with tablets were withdrawn from the dissolution vessels, lightly blotted with a tissue paper to remove excess liquid and reweighed. The percent water uptake, i.e. degree of swelling due to absorbed test liquid, was estimated at each time interval using following equation:

% Water uptake / polymer swelling = (Ws-Wi) × 100

Where Ws is the weight of the swollen tablets at time t and Wi is the initial weight of the tablets.

Fig.3 Release profile of Guar gum Compression coated tablets of Ketoprofen

F8 300 mg guar gum coat, F9 400 mg guar gum coat, F13 300 mg guar gum coat (AC-Di-Sol in core tablets), F13 300 mg guar gum coat with rat caecal contents.

Fig.4 Release profile of Locust bean gum compression coated tablets of Ketoprofen.

F11 300 mg Locust bean gum coat, F12 400 mg Locust bean gum coat, F14 300 mg Locust bean gum coat (AC-Di-Sol in core tablets), F14 300 mg Locust bean gum coat with rat caecal content.

Differential scanning calorimetry:

The possibility of any interaction between Ketoprofen and polymers during the tablet processing was assessed by carrying out the thermal analysis on pure drug (Ketoprofen), gum, tablet formulations using Differential scanning calorimetry. Samples (10 mg) were accurately weighed into aluminum pans and then hermetically sealed with aluminum lids. The thermograms of the samples were obtained at a scanning rate of 2 ⁰C / min. The obtained thermographs were used to decide any interaction between Ketoprofen and polymers.

RESULTS AND DISCUSSION:

The present study was aimed at developing oral colon targeted formulations for Ketoprofen using guar gum and locust bean gum as carrier. It was reported earlier that guar gum could be used as a carrier for colon-specific drug delivery in the form of either a matrix tablet or as a compression coat over a drug core tablet^[8][9]. Locust bean gum had also been studied along with chitosan as a carrier for colonic drug delivery^[10]. Hence both the gums were used as carrier in the matrix tablet as well as applied as a coat on drug core tablet.

Fig. 5: Plot of percent swelling or water uptake of Ketoprofen formulation F3, F6, F13, F14 as a function of time.

F3- Guar gum matrix tablet of Ketoprofen, F6- Locust bean gum matrix tablet of Ketoprofen, F13- Guar gum press coated tablets of Ketoprofen, F14- Locust bean gum press coated tablets of Ketoprofen.

Matrix tablets of Ketoprofen:

All tablets showed uniform thickness. The percentage friability for all the formulations was below 1% indicating that the friability was within the prescribed limits. All the tablets showed acceptable weight variation and hardness. Hardness of tablets was found to be in the range of 4.4-4.8 kg. The matrix tablets were found to contain 99.1-100.37 % of the labeled amount of Ketoprofen.

The matrix tablets were subjected to in vitro drug release studies in 0.1 N HCl for 2hrs, in pH 6.8 phosphate buffer for 3hrs, the study was further continued in pH 7.4 phosphate buffer. The release profile of guar gum matrix and locust bean gum matrix tablets of Ketoprofen are given in Fig.1 and Fig.2. Ketoprofen tablets containing guar gum and locust bean gum in the ratio of 1:0.25 (drug: gum) gave initial burst effect due to low concentration and hydrophilicity of gums. It can be observed from the Fig.1 and Fig.2 that as the concentration of the gum in the matrix formulations was increased the initial burst effect was decreased. This might be due to hydration and swelling of gums on exposure to dissolution fluid. It was also observed that release through locust bean gum matrix tablets was more as compared to guar gum due to less hydration and swelling Within 5hrs of dissolution study guar gum and locust bean gum matrix tablets released about 60 and 80% of ketoprofen respectively. The results, thus, showed that the matrix formulations of ketoprofen containing either guar gum or locust bean gum failed to control the drug release up to 5 h of dissolution i.e. in the physiological environment of stomach and small intestine.

Fig.06 Differential scanning colorimetric thermograms of Ketoprofen compression coated tablet formulations.

(a) Ketoprofen.(b) Compression coated tablet formulation containing 300 mg of guar gum.(F13) (c) Compression coated tables formulation containing 300 mg of locust bean gum.(F14)

Compression coated tablets of Ketoprofen using gum coat:

As the matrix tablets failed to delay the release, compression coated tablets of Ketoprofen were prepared to control the drug release up to 5 h of dissolution study. Fast disintegrating ketoprofen core tablets were prepared by incorporating 3% ac-di-sol. The hardness of core tablets was found to be in the range 2.5-3.0 Kg and they contained 99.2-100.4 % of the labeled amount of Ketoprofen showing uniformity of drug content. The disintegration time of core tablets was found to be less than one minute.

The compression coated tablets of ketoprofen showed hardness in the range 6-7 kg. Release profile of Guar gum and Locust bean gum compression coated tablets of Ketoprofen are given in Fig 3 and Fig.4. When the tablets were subjected to In vitro drug release, Ketoprofen tablets coated with 200 mg of gum coat were not intact even up to 5 h of dissolution study. This might be due to uneven coating of drug around rhe tablet. Ketoprofen tablets coated with 300 mg of guar gum and locust bean gum released about 9% and 4% of Ketoprofen respectively and tablets coated with 400mg of guar gum and locust bean gum released about 2% and 3% of Ketoprofen respectively in the physiological environment of stomach and small intestine i.e. up to 5 h of dissolution study.

When the further dissolution was continued after 5 h of dissolution, tablets coated with 300 mg of guar gum and locust bean gum released about 13% and 6% of Ketoprofen respectively and tablets containing 400 mg of guar gum and locust bean gum coat released about 6% and 5% of Ketoprofen respectively up to 9 h of dissolution study. It was observed that as amount of guar gum coat applied was increased the release of drug was decreased because of formation of thicker coat of gum around the tablet. In case of locust bean gum coated tablet, there was not much difference in the further release of Ketoprofen in both coat formulations. Thus 300 mg of gum coat was found to be sufficient to delay the release of ketoprofen.

The dissolution study of tablets, coated with 300mg of gums, was continued in the rat caecal content medium after 5 hrs of dissolution which is shown in Fig. 3 and Fig. 4. It was observed that tablets compression coated with 300 mg of guar gum coat and locust bean gum released 14 % and 6% of Ketoprofen respectively after 9 h study without rat caecal content medium but when dissolution was continued in presence of rat caecal content medium after 5 hrs of dissolution study same tablets released 73 % and 44% of ketoprofen respectively due to biodegdration of gum coat. The tablets compression coated with 300 mg of guar gum released more Ketoprofen as compared to locust bean gum in presence of rat caecal content. (This may be due to the fact that guar gum consists of linear chains of β D-mannopyranosyl units linked (1→4) with single member α-D-galactopyranosyl units and ratio of D galactose to D mannose is 1:2.and locust bean gum consist of 1→4 linkage β-D-mannopyranose backbone with branch points from their 6-positions linked to α-D-galactose (i.e. 1→6-linked α-D-galactopyranose) and ratio of D galactose to D mannose in guar gum is 1:2 which 1:4 in case of locust bean gum). As colonic bacteria are responsible for breaking this linkage between galactose and mannose, degradation is faster in guar gum as compared to locust bean gum.

Polymer swelling / Water uptake study:

The water uptake data were subjected to the Vergnaud model (1993) to determine the rate of water uptake. The generalized form of the Vergnaud model is as follows:

M_t=ktⁿ

Where M_t represents the amount of liquid transferred at time t, and k is the swelling constant which depends upon the amount of liquid transferred after infinite time, the porosity of matrix (this term was substituted for the shape of the matrix in the original equation),and diffusivity. The exponent n indicates the mechanism of the water uptake.

The plot of % water uptake vs. time is shown in Fig.5. Kinetic constants (k), swelling exponents (n), and correlation coefficients (r²) obtained from plots of log % water uptake vs. log time are given in Table no.5.

Guar gum and locust bean gum matrix tablets after 7 hrs of water uptake study showed the 135 % and 130 % of water uptake respectively (Fig. 5). It is evident from above plot that guar gum and locust bean gum matrix of Ketoprofen indicate slower hydration or water uptake (Fig. 5.) As compared to locust bean gum, guar gum showed more water uptake as well as higher hydration rate. The hydrophilic polymer on contact with an aqueous medium gradually begins to hydrate from periphery towards the centre forming a gelatinous swollen mass which controls the diffusion of drug molecules through the polymeric material into the aqueous medium. The % water uptake of guar gum and locust bean gum as a coat over the core tablets (F13 and F14) was found to be 320% and 234% respectively after 7 hrs of study. The hydrophilic polymers such as guar gum and locust bean gum as compression coat to core tablets underwent hydration as soon as they came in contact with test medium, and that the polymer hydration continued up to 7 hrs (Fig.5).

A value of ≤ 0.5 for n indicates a diffusion controlled mechanism in which the rate of diffusion of the liquid is much less as compared with rate of relaxation of the polymer segment. A value of n (n=1) suggest that the liquid diffuses through the polymer at constant velocity showing an advancing front marking the limit of liquid penetration. A value of n between 0.45 and 1 indicates an anomalous or complex behavior in which the rate of diffusion of the liquid and that of relaxation are of the same magnitude.

Accordingly, it can be inferred that kinetics of swelling or water uptake by guar gum matrix (F3) and locust bean gum matrix (F6) follows an anomalous or complex behaviors (0.45<n >1). The exponent, n, for guar gum and locust bean gum press coated tablets of Ketoprofen with plain core indicates a diffusion controlled mechanism (F13, F14).

Differential Scanning Calorimetry:

DSC thermal curve of Ketoprofen showed a single sharp endothermic peak at its melting point. Some modifications of Ketoprofen melting peak such as changes in area, shape or peak temp were found. The thermograms of the formulations did not show any significant shift in the endothermic peak (Fig.6). Based on the thermograms of DSC, there appears to be no interaction between Ketoprofen and polymer in the tablet formulations.

CONCLUSION:

The present studies were carried out to develop colon targeted drug delivery system for Ketoprofen for local action in the colon. Matrix tablets of Ketoprofen failed to control the release of Ketoprofen and deliver the drug to colon. The fast disintegrating compression coated tablets of Ketoprofen containing 300 mg gum coat controlled the release in the physiological environment of stomach and small intestine i.e. up to 5 h of dissolution study, and showed increased release i.e. 73 % of drug release in presence of rat caecal content medium in 9 hrs of dissolution study due to degradation of gum. It appears that Ketoprofen tablets coated with 300 mg of guar gum coat are most likely to provide targeted delivery of Ketoprofen to the colon.

ACKNOWLEDGEMENTS:

The authors gratefully acknowledge BEC Chemical Pvt. Ltd, Mumbai for sample of Ketoprofen and Lucid colloids Ltd, Mumbai for the gift samples of guar gum and locust bean gum.

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Received on 14.05.2009 Modified on 17.07.2009

Research J. Pharm. and Tech.2 (4): Oct.-Dec. 2009; Page 771-776