INTRODUCTION:

Pharmaceutical invention and research are increasingly focusing on delivery systems which enhance desirable therapeutic objectives while minimizing side effects. Oral drug delivery system represents one of the frontier areas of drug delivery systems. Such a dosage form manages common concern which exists in area of cost-efficient treatment, patient compliance, optimum drug delivery and bioavailability¹. The last two decades there has been a remarkable improvement in the field of novel drug delivery systems. Carrier technology offers an intelligent approach for drug delivery by coupling the drug to a carrier particle such as microspheres, nanoparticles, liposomes, etc, which modulates the release and absorption characteristics of the drug².

Microspheres constitute an important part of this particulate drug delivery system by virtue of their small size and efficient carrier characteristics. However, the success of this novel drug delivery system is limited due to their short residence time at the site of absorption. It would therefore be advantageous to have means for providing an intimate contact of the drug delivery system with absorbing gastric mucosal membranes³. Microspheres are characteristically free powders consisting of proteins or synthetic polymers that are biodegradable in nature and ideally having a particle size less than 200μm⁴.

Colon specific drug delivery systems have gained increasing attention for the treatment of diseases such as Chrohn’s disease, ulcerative colitis and irritable bowel syndrome⁵. Ulcerative colitis is a type of inflammatory bowel disease (IBD) that affects the lining of the large intestine (colon) and rectum. Repeated swelling (inflammation) leads to thickening of the intestinal wall and rectum with scar tissue. Death of colon tissue or severe infection (sepsis) may occur with severe disease⁶. Mesalamine (5-ASA) is an anti-inflammatory drug used to treat crohn’s disease and ulcerative colitis. Since Mesala-mine (5-ASA) is largely absorbed from the upper intestine, selective delivery of drugs into the colon may be regarded as a better method of drug delivery with fewer side effects and a higher efficacy⁷.

In the present study, an attempt has been made to prepare mesalamine microspheres prepared by ionotropic gelation method using chitosan as polymer and sodium tripolyphosphate (TPP) as the cross-linking agent. Chitosan is a biodegradable natural polymer with great potential for pharmaceutical applications owing to its biocompatibility, non-toxicity and mucoadhesive properties. TPP is an extensively researched well established, charged, non-toxic, multivalent, anionic cross-linking agent with five bonding sites on the molecules.

MATERIALS AND METHODS:

Materials:

Mesalamine was obtained from Zydus Cadila, Ahmedabad, India. Chitosan was a gift sample from Central Institute of Fisheries Technology, Cochin. Eudragit S100 was obtained from Ranbaxy Laboratories Limited, New Delhi, India. TPP was purchased from Loba Chemicals. All other chemicals used in experiment were of analytical grade and used as such.

Preparation of microspheres:

Cross linked chitosan microspheres were prepared using ionic-gelation emulsion method. Chitosan solution (4% w/v) was prepared in 5% aqueous acetic acid solution in which the drug was previous-ly dissolved and dispersed in liquid paraffin containing span 80(1%w/v) (Gawde and Agrawal, 2012). The dispersion was stirred using a specially fabricated stainless steel half-moon paddle stirrer and saturated aqueous solution of TPP (1ml to 3ml), a cross-linking agent was added with continuous stirring. The stirring was continued for 4 h, prepared microspheres were centrifuged, washed twice with hexane to remove oily phase from the solution and acetone and were then dried in vacuum desiccators for 48 hrs.

In-vitro release studies:

The drug release rate from the microspheres was studied in a medium of changing pH using the dissolution apparatus II at 37±0.5°C with a rotation speed of 100rpm. A weighed amount of mesala-mine microspheres (equivalent to 50mg of drug) were added to dissolution medium (350ml of 0.1N HCl, pH 1.2) for the first two hours. At the end of second hour, the pH of the dissolution medium was raised to 4.5 by the addition of 250ml solution composed of 3.75g of KH2PO4 and 1.2g of NaOH. At the end of fourth hour pH was raised to 7.4 by adding 300ml of phosphate buffer concentrate (2.18g of KH2PO4 and 1.46g of NaOH in distilled water) (El-Bary et al., 2012). At predetermined time inter-vals, 5ml sample was withdrawn, passed through a 0.45μm membrane filter (Millipore). After appropriate dilutions, the concentration of drug in samples was analysed spectrophotometrically at predetermined λ_max(s). The initial volume of dissolution medium was maintained by adding 5ml of fresh dissolution medium after each withdrawal. Perfect sink conditions prevailed during the drug release studies.

Statistical analysis:

The results were expressed in mean ± S.D. One way ANOVA (Analysis of Variance) was performed for studying the statistical significance using Minitab 15 software. Values of p< 0.05 were considered to be significant.

RESULTS AND DISCUSSION:

Identification by FT-IR spectrophotometer:

FTIR studies of mesalamine and prepared formulation is shown in Figure 1 and 2. It is clear from the FTIR that the characteristic peaks of the drug are also present in the formulation depicting no incompatibility between the drug and polymers in the formulation.

Morphology and particle size:

Visual examination of the SEM indicated that the microspheres of mesalamine were spherical with varied surface roughness (Figure 3). The particle size of microspheres ranged from 61.22-90.41μm and were found to increase with increasing polymer content (p<0.05) (Table 2). As the emulsifier concentration was increased from 0.5 to 1.5ml, the particle size was found to increase in the prepared formulations (p<0.05).

In vitro release studies:

In the in-vitro release studies, changing the pH conditions was attempted in lieu to mimic the GI conditions without enzymes. The pH condition used was pH 1.2 for a period of 2 h (stomach), pH 4.5 (duodenum) for 2 h followed by pH 7.4 (distal ileum and colon) for the remaining duration of the study. A successful colon targeted drug delivery should have minimum drug release during its transit in the stomach and upper intestine to ensure maximum drug release in the colon⁸.

Eudragit S100 is an anionic copolymer of methacrylic acid and methyl methacrylate, the ratio of free carboxyl groups to the ester groups is approximately 1:2. It exhibits a dissolution threshold pH slightly above 7.2⁹. Due to the pH-sensitive property of this polymer, it was selected to avoid the rapid dissolution of mesalamine during the initial transit of the microspheres through the gastric cavity and the upper small intestine¹⁰.

The retardation in drug release was found to be significant with increasing polymer concentration (p<0.05). The increased density of polymer matrix at higher concentration resulted in an increased diffusion pathlength. This may decrease the overall drug release from the polymer matrix¹¹. Furthermore, smaller microspheres are formed at lower polymer concentration and have a larger surface area exposed to dissolution medium, giving rise to faster drug release¹⁰. However, increase in emulsifier concentration in the formulations showed insignificant results in the drug release rate (p>0.05). Eudragit coating of chitosan microspheres prevented the release of drug in stomach and targeted the delivery of drug to colon¹².

It was found that formulations with drug-polymer ratio of 1:1 (M1 to M3) released complete drug at 12 hours¹³. A comparison of percentage release of drug from cross-linked chitosan microspheres vs time without coating is shown in Figure 5. A comparative % drug release of chitosan microspheres (M3, M6 and M9) coated with Eudragit S-100 with drug-polymer ratio 1:1, 1:2 and 1:3, respectively at 1.5ml emulsifier concentration is depicted in Figure 6. It was observed that Eudragit S100 coated chitosan microspheres gave no release in the simulated gastric fluid, negligible release in the simulated intestinal fluid and maxi-mum release in the colonic environment¹⁴.

CONCLUSION:

Mesalamine microspheres were prepared successfully by using the ionic-gelation emulsification method. Prepared microspheres showed good % yield and drug loading. Encapsulation efficiency of micro-spheres was good for all formulations. The prepared microspheres with 1:3 ratio of drug-polymer coated with Eudragit S100 (M9) was found suitable for colonic release of mesalamine resisting drug release in gastric medium, minimizing release in the upper intestinal region and showing maximum release in the colonic region. Therefore, the developed formula-tion proves to be promising for the colon targeted drug delivery of mesalamine and thereby facilitating in the management of ulcerative colitis.

Figure 1: SEM of mesalamine-loaded chitosan microspheres.

Figure 2: A comparison of percentage release of drug from cross-linked chitosan microspheres vs time (in hours) without coating.

Table 1: Formulation composition of cross linked chitosan polymer.

Sl. No.	Formulation Code	Drug: Polymer	Emulsifier concentration (ml)
1	M1	1:1	0.5
2	M2	1:1	1.0
3	M3	1:1	1.5
4	M4	1:2	0.5
5	M5	1:2	1.0
6	M6	1:2	1.5
7	M7	1:3	0.5
8	M8	1:3	1.0
9	M9	1:3	1.5

Figure 3: A comparative % drug release of chitosan microspheres (M3, M6 and M9) coated with Eudragit S-100 polymer.

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Received on 26.03.2021 Modified on 24.04.2021

Research J. Science and Tech. 2021; 13(3):165-169.

DOI: 10.52711/2349-2988.2021.00025