1. INTRODUCTION:

Targeting of drugs specifically to the colon is advantageous in the treatment of diseases such as irritable bowel syndrome, amoebiasis, Crohn’s disease, ulcerative colitis, and colorectal cancer.[1]

The colon is a site where both local and systemic drug delivery can take place. Drugs, which are destroyed by the stomach acid and/or metabolized by pancreatic enzymes, are slightly affected in the colon, and sustained colonic release of drugs can be useful in the treatment of targeted disease. Likewise, colonic delivery of vermicides and colonic diagnostic agents require smaller doses. There are several approaches of colon-specific drug delivery such as multi-coating with pH-dependent polymers, design of timed-release dosage forms and the use of carriers that are degraded by colonic bacteria etc.[2]

Various drugs like mesalamine, tinidazole, metoclopramide, cisapride, tegaserod, erythromycin, etc are used in colonic disorder. [3]

Tegaserod is being developed as a treatment for constipation-predominant irritable bowel syndrome (IBS). Tegaserod is a potent partial agonist of serotonin type-4 (5-HT4) receptors located in the GI tract. The mechanism of action of Tegaserod is reflected in its stimulation of the peristaltic reflex intestinal secretion, as well as inhibition of visceral sensitivity via activation of 5-HT4 receptors in the gastrointestinal tract. Tegaserod acts as a partial agonist at neuronal 5-HT4 receptors triggering the release of further neurotransmitters such as calcitonin gene related peptide from sensory neurons. [4]

The recommended dosage of Tegaserod is 6 mg (i.e equivalent to 8.3 mg of Tegaserod maleate) [5,6] taken twice daily orally before meals for 4-6 weeks. Tegaserod is rapidly absorbed following oral administration; peak plasma concentrations are reached after approximately 1 hour. Tegaserod is approximately 98% bound to plasma proteins, primarily to α1-acid glycoprotein. The plasma clearance of Tegaserod is 77 ±15 L/h, with an estimated terminal half-life (t1/2) of 11 ± 5 h following intravenous administrations. Approximately two-thirds of the orally administered dose of Tegaserod is excreted unchanged in the feces, with the remaining one third excreted in the urine, primarily as the main metabolite. [1]

Aim of this study was to explore the feasibility of time and pH dependent enteric-coated matrix system for treatment of irritable bowel syndrome and constipation with single daily dose of tegaserod. Besides, it was intended to exploit the typical pharmaceutical coating technology to attain the time and pH dependent colon-specific drug delivery.

Hence, it is worthwhile to formulate and evaluate colon specific tablet by using suitable polymer. So, an attempt will be made to formulate a dosage form, which could be formulated easily, using the usual tableting techniques and usual tableting ingredients, with little modification in the method of processing of the ingredients.

2. MATERIALS AND METHODS:

2.1 Materials

Tegaserod maleate, CAP, Hydroxy propyl methyl cellulose K4M and K15M, Eudragit L100 and S100, magenesium stearate, talc, Microcrystalline cellulose, PVP K30.

2.2 Preparation of matrix tablets

The batches were prepared by using linear model response surface methodology in D-optimal point exchange model of design expert software.(Table 1). Batches were prepared by wet granulation technique by using 8.31mg of drug and polymers were used as follows. The total tablet weight was 130mg. The drug and excipients except talc and magnesium stearate were weighed accurately were passed through sieve #60 and this mixture was kneaded with 10% of PVP K30 solution in IPA. This wet mass was passed through sieve # 7 and granules were dried at 45 °C for 15 minutes following drying in air for 10 minutes. Dry granules were passed through sieve # 36. Weighed amount of talc and magnesium stearate was added at the time of compression.

2.3 Preparation of Coating Solution

5%w/v coating solution of CAP, was prepared by dispersion of CAP in IPA first by stirring and addition of methyl chloride for 10 minutes and then by stirring for another 20-25 minutes. Lastly Propylene glycol was added. Solution was filtered through nylon cloth and volume of the solution was measured (Table 2).

2.4 Coating Method [7]

The prepared concave tablets were loaded to a coating pan and heated for 20 min with the help of hair dryer. The tablets were coated by spray coating using spray gun. The pan speed was kept at 15 rpm and temperature of hot air at temperature of 40˚C was blown over the tablets using hair dryer to dry the coated tablets. The tablets were coated till it attains predetermined weight i.e. the % coating becomes 10%. Finally coated tablets were dried at 40˚C for 10-15 minutes (Table 3).

2.5 In-vitro Release:

The release rate of tegaserod maleate was determined using USP dissolution testing apparatus II (Paddle type). The dissolution test was performed using 900 ml of 0.1 N HCl, at 37 ± 0.5°C and speed of 75rpm for 2hrs. Aliquot (10 ml) of the solution was collected from the dissolution apparatus hourly and were replaced with fresh dissolution medium. After this the dissolution medium was replaced with 900 mL phosphate buffered (pH 6.8), and the dissolution continued for another 6 hrs. Then study at a pH of 7.4 buffer medium is carried out till completion of 12-15hr at 75rpm and 37±0.50C. The experiments in rat fecal slurries and in without rat fecal slurries were carried at pH 7.4. The aliquots were filtered through whatmann filter. Absorbance of these solutions was recorded at 220nm and 221nmfor pH 6.8 and pH 7.4 respectively. Aliquots were withdrawn at one hour interval from a zone midway between the surface of dissolution medium and the top of rotating paddle not less than 1 cm apart from the vessel wall. Drug content in dissolution sample was determined by software (PCP disso v2.08) version.

2.6 Differential scanning calorimetry (DSC) analysis [8]

Thermographs of pure drugs were studied. An empty aluminium pan was used as reference.DSC measurement was performed at a heating rate of 50C /min from 25 to 300˚C using aluminium sealed pan .During the measurement, the sample size was 5-10 mg for each measurement and sample cell was purged with nitrogen gas (Fig. 4, 5, 6)

3. RESULTS AND DISCUSSION:

The granules (F1-F12) were evaluated for the parameters like angle of repose, bulk density, tapped density, Carr’s compressibility index, Hausner’s ratio (Table 4). The uncoated tablets (F1-F12) were evaluated for the parameters like hardness, thickness, friability, weight variation and drug content (Table 5). The tablets (F1-F12) were evaluated for the parameters like hardness, thickness, diameter, thickness of coating (Table 6). The results complied with the official requirements.

3.1 In-vitro release studies

The results of the drug release studies carried out on tegaserod maleate tablets coated with different ratio of the polymers in simulated gastric (pH 1.2) and small intestinal (pH 6.8) and colonic fluid (pH 7.4) [9-14]. The studies were also carried out rat fecal matter only to study the microbial degradation of drug for the optimized batch.

From the data (Fig. 2) it was found that F8 and F9 formulation containing 7.5% and 10% of Eudragit S-100 showed delayed release. Though Eudragit S-100 showed the delayed release it was also difficult to maintain the uniformity of drug and polymers on the large scale. Therefore, this formulation can’t be considered for the further studies. Better release profile was seen in Eudragit L-100 25% (F12) showing the release of nearly 92% and also, the release was very less in small intestine. The other, 10% and 17.5% of Eudragit L-100 (F10 & F11 respt.) shows comparatively less release than 25%. So, increase in the concentration of L-100 shows good release. In the case of F1 formulation of HPMC K4M 5% it shows 92.150% drug release, from the graph it can be seen that there is the arrival of plateau state and drug can be nicely controlled further than, F2 and F3 i.e 85.92% and 84.559% respectively, which do not show any signs of controlled release (Fig.1) So, increase in the concentration of K4M, decreases the drug release. The formulation F1 is also been less cost effective. The release data was fitted to various mathematical models to evaluate the kinetics and mechanism of the drug release. Zero order was best fitted model with greater r2 value than other. F4, F5 and F6 formulation of HPMC K15M showed release of 72.44%, 81.48%, and 90.25% respectively. So, the release was comparatively slow as that of HPMC K4M batches. So, the optimized batches from the above results were found to be F1 and F12.

The dissolution studies of the optimized formulation F1 and F12 of enteric coated tablets revealed in the presence of 10% of rat faecal matter in 900ml of dissolution medium. The release was compared with the same formulation, without faecal matter. It was found that the percent release greatly increased due to the microbial degradation of the drug. This indicates that the activity of microbial flora towards the degradation of drug (Fig.3).

The formulation purely follows the Fickian diffusion controlled mechanism. The formulations show zero order and Peppas model kinetics as shown in Table 7. The best fit model was found to be zero order for most of the batches.

3.2 Differential scanning calorimetry

DSC thermogram of the optimised formulation showed that there was no any major difference in onset temperature and peak temperature, when compared with pure drug’s thermogram as shown in Fig. 4, Fig. 5, Fig. 6.

3.3. Stability studies

The selected formulations F12, F13 and F14 were stored in closed glass containers on the shelf, at 25°C/ 40% RH for 12 months (climatic zone III conditions for long term testing). The protocol of the study was in accordance with the recommendation in the WHO document for stability testing. At each sampling time (every 3 months), the formulations were tested for their mechanical strength, drug content and in vitro drug drug release. In addition, no changes in drug content and mechanical strength of all the tablet formulations were observed during the storage period.

4. CONCLUSION:

It may be concluded from the present study that slow and controlled release of tegaserod maleate over a period of 24 hours was obtained (F1 to F12) use of hydrophilic polymer like HPMC K4M (10%) was successful in the formation of enteric coated tablet and at the same time it is effective in retarding the drug release and same for Eudragit L100 (25%). Among all the formulation, F1 shows that 92.15% and F12 shows that 92.648% at the end of 16 hours. The cumulative percentage drug release was decreased by increase in polymer concentrations of HPMC K4M and vice versa for Eudragit L-100.Also the colonic flora increases the release of drug. The mechanism of the drug release from F1 and F12 was quasi (Fickian) diffusion, zero order release kinetics which met the rule of controlled drug delivery system.

From the data of bioavailability study, the proposed enteric coated tegaserod maleate (6 mg) HPMC K4M or EudragitL-100 tablet per day could be used in place of twice doses of 6mg tegaserod conventional tablet and with better control of drug release for targeted drug delivery, which might improves patient compliance and reduces gastric side effects. In summary, time and pH dependent controlled release mechanisms could achieve colonic specific drug delivery of tegaserod following oral administration. Developed CDDS are relatively economical and easy to be manufactured by conventional pharmaceutical coating technique and is a promising candidate for specific drug delivery to the colonic region, in particular for tegaserod of this study.

Table 1: Composition of tegaserod maleate colon specific tablets (tablet weight = 130mg)

Batch No.	Drug (mg)	HPMC K4M (%)	HPMC K15M (%)	Eudragit S100 (%)	Eudragit L100 (%)	Talc (%)	Mg. stearate(%)	MCC
F1	8.31	10	-	-	-	2	2	q.s
F2	8.31	15	-	-	-	2	2	q.s
F3	8.31	20	-	-	-	2	2	q.s
F4	8.31		10	-	-	2	2	q.s
F5	8.31	-	15	-	-	2	2	q.s
F6	8.31	-	20	-	-	2	2	q.s
F7	8.31	-	-	5	-	2	2	q.s
F8	8.31	-	-	7.5	-	2	2	q.s
F9	8.31	-	-	10	-	2	2	q.s
*F10*	8.31	-	-	-	10	2	2	q.s
*F11*	8.31	-	-	-	17.5	2	2	q.s
*F12*	8.31	-	-	-	25	2	2	q.s

Table 4: Evaluation of granules of tegaserod maleate

Formulation	Angle of repose (θ)	Bulk density (g/ml)±SD	Tapped density (g/ml)	Carr’s Compressibility Index(%)	Hausner’s ratio
F1	19.5±0.75	0.495±0.45	0.502±0.008	7.05±0.02	1.01±0.05
F2	28.0±0.53	0.302±0.02	0.35±0.02	13.7±0.01	1.15±0.02
F3	28.3±0.63	0.391±0.02	0.445±0.01	12.13±0.07	1.13±0.02
F4	20.7±0.64	0.359±0.03	0.410±0.008	12.43±0.08	1.14±0.05
F5	28.8±0.35	0.211±0.02	0.23±0.02	8.26±0.01	1.08±0.04
F6	21.2±0.65	0.323±0.06	0.38±0.04	15.02±0.03	1.17±0.06
F7	24.4±0.33	0.427±0.03	0.50±0.06	15.44±0.02	1.18±0.06
F8	28.3±0.75	0.308±0.06	0.35±0.072	13.96±0.07	1.13±0.02
F8	20.2±0.36	0.391±0.04	0.48±0.027	20.04±0.03	1.22±0.01
F9	25.2±0.28	0.404±0.02	0.47±0.036	14.40±0.03	1.16±0.06
F10	27.6±0.71	0.207±0.01	0.22±0.065	7.17±0.01	1.07±0.02
F11	24.8±0.30	0.306±0.04	0.36±0.018	6.8±0.02	1.2±0.05
F12	18.6±0.64	0.212±0.06	0.22±0.013	7.50±0.02	1.08±0.02

Table 5: Evaluation of Uncoated tablet batches

Formulation	Hardness (Kg/cm2)	Thickness (mm)	Friability (%)	Weight variation (mg)	Drug content (%)
F1	5.8±0.6	2.58±0.7	0.010±0.05	128±0.5	99.87±0.95
F2	5.4±0.4	2.9±0.5	0.043±0.06	124±0.8	98.06±1.06
F3	5.7±0.3	2.78±0.3	0.056±0.02	125±0.3	98.12±0.2
F4	4.8±0.5	2.71±0.05	0.011±0.01	130±0.6	97.34±0.7
F5	5.1±0.2	2.85±0.8	0.051±0.07	131±0.2	98.63±0.3
F6	5.2±0.5	2.59±0.6	0.083±0.02	128±0.3	98.28±1.3
F7	5.5±0.9	2.85±0.4	0.027±0.08	132±0.8	97.14±0.2
F8	5.9±0.08	2.77±0.09	0.06±0.03	129±0.5	98.38±0.99
F9	5.1±0.6	2.72±0.8	0.048±0.06	129±0.7	96.76±1.26
F10	5.3±0.5	2.93±0.01	0.045±0.05	127±0.4	98.38±0.93
F11	4.7±0.02	2.96±0.07	0.039±0.03	131±0.1	96.39±1.2
F12	5.0±0.05	2.86±0.4	0.03±0.02	130±0.5	99.04±0.48

Table 6: Evaluation of coated tablet batches

Formulation	Hardness (Kg/cm2)	Thickness (mm)	Diameter (mm)	Thickness of coating (mm)
F1	7.8±0.07	2.83±0.7	7.85±0.4	0.25±0.3
F2	7.4±0.2	3.06±0.05	8.06±0.2	0.16±0.7
F3	6.8±0.7	3.05±0.4	8.05±0.04	0.27±0.2
F4	7.2±0.8	2.98±0.05	8.16±0.03	0.27±0.9
F5	7.7±0.6	3.05±0.6	8.04±0.7	0.19±0.7
F6	6.2±0.3	2.83±0.3	8.12±0.04	0.24±0.4
F7	7.9±0.3	3.05±0.1	8.04±0.7	0.2±0.8
F8	8.0±0.6	3.19±0.02	8.07±0.4	0.42±0.7
F9	7.1±0.4	3.01±0.03	8.07±0.8	0.29±0.1
F10	7.7±0.9	2.97±0.8	8.14±0.3	0.04±0.3
F11	8.1±0.2	3.17±0.6	8.11±0.5	0.21±0.2
F12	7.6±0.1	3.05±0.8	8.17±0.1	0.19±0.6

Table 7. Kinetic data for the prepared batches

Formulations	Best Fit Model	r2	k	n	Formulations	Best Fit Model	r2	k	n
F1	Zero Order	0.9952	9.034	0.4930	F7	Zero Order	0.9939	7.879	0.4231
F2	Zero Order	0.9914	8.943	0.4211	F8	Peppas model	0.9895	0.3457	0.4637
F3	Peppas model	0.9897	0.1660	0.3786	F9	Peppas model	0.9846	0.7294	0.3107
F4	Zero Order	0.9851	7.239	0.3751	F10	Zero Order	0.9927	9.064	0.4553
F5	Zero Order	0.9939	8.786	0.4237	F11	Peppas model	0.9811	7.679	0.4231
F6	Peppas model	0.9877	0.3689	0.3128	F12	Zero Order	0.9957	9.264	0.4751

Fig 4: DSC thermogram of mixture of pure drug tegaserod maleate

Fig 5: DSC thermogram of mixture of tegaserod maleate and HPMC K4M

Fig 6: DSC thermogram of mixture of tegaserod maleate and eudragit L-100

5. REFERENCES:

[1] Camilleri M. Review article: Tegaserod. Aliment Pharmacol Ther., 2001; 15: 277-89.

[2] Jose S, Dhanya K, Cinu TA, et al. Colon targeted drug delivery: Different approaches. Journal of Young pharmacists. 2009; 1: 13-19.

[3] Dipiro JT, Talbert R, Pee GC. Pharmacotherapy: A Pathophysiological Approach. 6th ed. Mc Graw-hill Medical Publishing Division, Newyork., 2005; 689-690.

[4] Drug Bank of Tegaserod [cited 2009 Nov 27]. Available from: http://www. DrugBank Showing Tegaserod (DB01079).

[5] Zhang H, Ibrahim AA. An in vitro evaluation of a chitosan-Containing multiparticulate system for macromolecule delivery to the colon. Int J Pharm., 1996; 239: 197-205.

[6] Zhang S, Thumma S, Chen G, et al. In vitro and in vivo evaluation of Tegaserod maleate pH-dependent tablets. European Journal of Pharmaceutics and Biopharmaceutics., 2008; 69: 247-254.

[7] Maestrelli F, Cirri M, Corti G,et al. Development of enteric-coated calcium pectinate microspheres intended for colonic drug delivery. Eur J of Pharm and Biopharm., 2008; 69: 508-18.

[8] Swarbrick J. Encyclopedia of pharmaceutical technology. 3rd ed. Vol. 2, Pharmaceutech,Inc, USA., 2007; 1228-33.

[9] Marvola M, Nykanen P, Rautio S. Enteric polymers as binders and coating materials in multiple-unit site specific drug delivery systems. Eur J Pharm Sci., 1999; 7: 259-267.

[10] Friend DR, George W, Chang. A Colon-specific drug delivery system based on drug glycosides and the glycosidases of colonic bacteria. J Med Chem., 1984; 27: 261-66.

[11] Patil N, Bhosale AV, Hardikar SR et al. Formulation and In vitro Evaluation of Microbially triggered Ibuprofen Delivery for colon targeting. Int J of PharmTech Res., 2009; 1: 328-333.

[12] Remon JP, Nathalie H, Vermeire A. In vitro evaluation of coating polymers for enteric coating and human ideal targeting. Int J of Pharm., 2005; 298: 26–37.

[13] Naikwade SR, Kulkarni PP, Jathar SR et al. Development of time and pH dependent controlled release colon specific delivery of tinidazole. DARU., 2008; 16: 119-27.

[14] Nagasamy VD, Reddy A, Samanta MK. Development and in vitro evaluation of colonic drug delivery systems for tegaserod maleate. Asian J of pharm., 2009;3: 50-53.

Received on 12.06.2014 Modified on 25.07.2014

Research J. Pharm. and Tech. 7(9): Sept. 2014 Page 1046-1051

Sr. No.	Composition	%
1	CAP	5% w/v
2	Methylene chloride	60% v/v
3	Isopropyl alcohol	40% v/v
4	Propylene glycol	1%v/v

Sr. No.	Parameter	Value applied
1	Preheating of tablets	15 to 20 mins.
2	Pan speed	15 rpm
3	Spray rate	Intermittent
4	Final heating of tablets after coating	10-15 mins