Colon Targeted Chitosan Microsphere Compressed Matrices for the Treatment of Ulcerative Colitis - A

Mr. Jitendra Kawadkar

During the last decade there has been interest in developing site-specific formulations for targeting drug delivery to the colon. The colon is a site where both local and systemic drug delivery can take place. A local means of drug delivery could allow topical treatment of inflammatory bowel disease, e.g. ulcerative colitis or Crohn’s disease.

Such inflammatory conditions are usually treated with glucocorticoids and sulphasalazine .Treatment might be more effective if the drug substances were targeted directly on the site of action in the colon. Lower doses might be adequate and, if so, systemic side effects might be reduced. A number of other serious diseases of the colon, e.g. colorectal cancer, might also be capable of being treated more effectively if drugs were targeted on the colon. Site-specific means of drug delivery could also allow oral administration of peptide and protein drugs, which normally become inactivated in the upper parts of the gastrointestinal tract. However, the permeability of the epithelium of the colon to peptide and protein drugs is fairly poor, and bioavailabilities are usually very low. Colon-specific systems could also be used in conditions in which a diurnal rhythm is evident, e.g. asthma, rheumatic disease, ulcer disease and ischemic heart disease. The incidence of asthmatic attacks is, for example, greatest during the early hours of the morning. Because dosage forms remain longer in the large intestine than in the small intestine, colon-specific formulations could be used to prolong drug delivery. The objective of the present study is to develop colon targeted drug delivery system for mesalazine (5-aminosalisylic acid, nonsteroidal anti-inflammatory drug) the active moiety of sulfasalazine using chitosan-HCl microspheres to thecolon for the treatment of ulcerative colitis. Colon specific delivery with a controlled release pattern provides more effective therapy for such inflammatory bowel disease. A colon specific drug delivery system (more effective therapy) releasing the drug at controlled rate should prevent drug release in the stomach (pH 1-2) and small intestine (pH 6.8) and start releasing the drug upon entry into the colon (pH>7).

Introduction

A great deal of research work has been devoted to specific drug delivery to the colon. Colon-specific drug delivery with a controlled release pattern provides more effective therapy for such chronic disease as irritable bowel syndrome and inflammatory bowel disease, including Chron’s disease and ulcerative colitis ¹.

5-ASA can not be simply given orally in the treatment of colitis because it is unstable in acid and is also absorbed by the small intestine ² . A colon specific drug delivery system releasing the drug at controlled rates should prevent drug release in the stomach and small intestine and start releasing the drug upon entry into the colon. Hydroxypropylmethylcellulose (HPMC) capsules, enteric coated with Eudragit FS 30D or Eudragit RL 100 disintegrate towards the distal small intestine and proximal colon. Thus coated tablets and capsules are targeted to the colon  ^{3, 4, 5}.

A study of controlled release systems for 5-aminosalisylic acid intended to be conveyed to the colon .5-aminosalisylic acid is known to be the active therapeutic moiety of sulfasalazine, a prodrug used for the treatment of ulcerative colitis and Chron’s disease ⁶. Since as many as 30% patients are unable to tolerate treatment with sulfasalazine, due to side effects and toxicity caused by its metabolite sulfapyridine. It is desirable to deliver 5-aminosalisylic acid specifically to the colon with low toxicity carriers ⁷.

Chitosan is used as the release controlling polymer in virtue of its well known biocompatibility and biodegradability. Chitosan has extensively been used to sustain and control drug delivery ^8,9,10. In the present study, commercial chitosan is converted into microspheres of chitosan-HCl which would be directly compressed, together with the drug 5-aminosalisylic acid, into matrices. After preparation of matrices they are developed into tablets or introduced into capsules and coated. The release of 5-aminosalisylic acid from such matrices and the susceptibility of drug release to the polymer degrading action of the caecal microflora are evaluated in vitro using rat caecal microflora in virtue of the similarity with human intestinal microflora. During matrix transit through distal small intestine and colon the pH of the matrix environment, although variable, should keep above the pKa of Chitosan that is, 5.6 ¹¹. 

Ulcerative colitis, Symptoms & Treatment -               

# Ulcerative colitis

Ulcerative colitis is a chronic inflammatory bowel disease in which extensive areas of the walls of the large intestine become inflammed and ulcerated. The motility of the ulcerated colon is often so great that mass movements occur most of the time, rather than the usual 10 to 30 min per day.The colon’s secretions are greatly enhanced ¹². As a result the patient has repeated bloody diarrheal bowel movements. In its most limited form it may be restricted to the distal rectum, while in its most extended form the entire colon is involved. However, 80% of the patients present with disease extending from the rectum to the splenic flexure, and only 20% have pancolitis. Although the causes of IBD remain unclear, considerable progress has been made recently in the identification of important pathophysiologic mechanisms ^{13, 14}. Some clinicians believe that it results from an allergic or immune destructive effect but it also could result from a colonic bacterial infection.

Table 1: Initial symptoms of Ulcerative Colitis.

# Disease activity index-

Disease activity indices are prediction rules used to measure the activity of disease objectively in order not only to judge response in clinical trials, but also and especially to choose which drug to administer and its optimal dose regimen. However, the use of these indices in clinical practice is limited. In UC, the activity of the disease is usually assessed primarily on the basis of clinical features. The classification in mild, moderate or severe disease, based on the some clinical parameters and laboratory findings (number of bowel movements, fever, presence of tachycardia, anemia, and sedimentation rate) is the most widely used clinical activity index in gastroenterological practice. However, although clinically useful, these criteria do not allow sufficient discrimination for the purpose of clinical studies ¹³.

Table 2: Ulcerative Colitis disease activity index.

 # Treatment for Ulcerative Colitis-

Drug classes for ulcerative colitis ¹⁵ -

(1)Antiinflammatory –

A. Oral -

        Drugs                                                    Dose

Ø      Sulfasalazine                                          2-6 gm/day

Ø      Olsalazine                                              1.5-3 gm/day

ØMesalazine                                            1.5-4.8 gm/day

B. Topical -

     Drugs                                                       Dose

Ø      Mesalazine enema                                      1-4 gm/day

Ø      Hydrocortison enama                                 80-200 mg/day

C.  Systemic –

         Drugs                                                       Dose

Ø      Prednisolone                                             20-60 mg/day

Ø      ACTH                                                       80-120 UIV

(2) Antimicrobials –

Metronidazole, ciprofloxacin, co-trimoxazole, cephalexin in sever cases.

(3) Immunosuppresents –

       Drugs                                                       Dose

Ø      6-Mercaptopurine                                    50-150 mg/day

Ø      Azathiopurine                                          50-150 mg/day

# Mechanism action of Mesalazine (5-ASA)-

Mesalazine is a therapeutic moiety of sulfasalazine. Mesalazine represents the first-line treatment of choice. It inhibits the cyclooxygenase and 5-lipoxygenase pathways of arachidonic acid metabolism. The later pathway is felt to be more important in inflammatory bowel disease and results in the reduction of LTB₄ and hydroxyeicostatetraenoic acid (5-HETE) levels.

Mesalazine also may act as a scavenger of reactive oxygen metabolites, reduce neutrophil and macrophage chemotaxis and phagocytosis and inhibit cytokine and immunoglobulin secretion by peripheral blood and intestinal mononuclear cells ¹⁶ .

# Adverse Effects-

Coated mesalazine is better tolerated than sulfasalazine. Side effects noted are nausea, diarrhoea, abdominal pain and headache. Rashes and hypersensitivity reactions are rare. Bone marrow depression and decreased sperm count has not occurred. Mesalazine has some nephrotoxic potential- it is contraindicated in renal and hepatic impairment ¹⁷ .

Chitosan-HCl Microsphere Compressed Matrices -

# Chitosan -

Chitosan is the most abundant polysaccharide, infact second only to cellulose. Chitosan is obtained by deacetylation of chitin. The main commercial sources of chitin are the shell wastes of shrimp, crab, lobster, krill, and squid. Chitosan is soluble at acidic pH, forming gel represent a sustained drug release form.

The crude chitosan is dissolved in aqueous 2 % w/v acetic acid. Then the insoluble material is removed giving a clear supernatant solution, which is neutralized with NaOH solution resulting in a purified sample of chitosan as a white precipitate. Further purification may be necessary to prepare medical and pharmaceutical-grade chitosan ¹⁸..

Table 3: Chemical & Biological properties of Chitosan ¹⁹  

Table 4: Specifications of Pharmaceutical Grade Chitosan ^{19, 20}

Chitosan is used in oral drug formulations to provide sustained release of drugs. Recently, it was found that chitosan is degraded by the microflora that is available in the colon. As a result, this compound could be promising for colon-specific drug delivery. Chitosan esters, such as Chitosan succinate and Chitosan phthalate have been used successfully as potential matrices for the colon-specific oral delivery.

# Chitosan-HCl microsphere preparation-

Microspheres of < 3 μm diameter were obtained by spray drying Ch-HCl aqueous solution prepared from a suspension of Ch in water.Ch dissolved completely by bringing the suspension to pH 4.7 by addition of 1N HCl. Non-dissolved material removed by filtration, a small aliquot of solution was evaporated to dryness, residue was weighed  and determined actual Ch-HCl concentration. Then the solution was diluted to a concentration and spray dried. Chitosan–HCl microspheres show highly swelling nature (water content, around 11%). 

# Microsphere compressed matrices-

Chitosan–HCl microspheres with 20% w/w 5-ASA are blended and directly compressed to get matrices. These matrices can be developed into tablets by compression with other ingredients or introduced into the capsules.These dosage forms are enteric coated with methacrylates hydrophobic polymers and coated with intermediate layer of acid soluble polymer HPMC. In colonic environment the drug release from matrices depend on the pH in matrices.Besides, colonic bacterial enzymes penetrate into the matrix and degraded the matrix material.

Ch-HCl matrices swelled to a much higher degree compared to the Ch based matrices.

The comparatively high drug weight fraction in matrices are meant to minimize the number of matrices need to make up the therapeutic dose ¹¹.

Advantages of colon targeted dosage form in comparison to conventional dosage form -

Figure 1: Drug release in Gastrointestinal Tract

Mechanism of Drug Release from Matrices -

Drug release from matrices is controlled release and it depends on-

 1. pH change in the matrices—

5-ASA is less soluble in acidic pH and more soluble in alkali pH. On changing the pH in chitosan-HCl microspheres from acidic to alkali, drug dissolves and diffuse out.

Table 5: Solubility of 5-ASA at acidic and alkali pH ¹¹

Colonic salts penetrates into the microsphere compressed matrices and increase internal pH.

Figure 2: Drug release from matrices on pH change

2. Colonic Bacterial Enzymes  

Chitosan is biocompatible, biodegradable and nontoxic in nature. Chitosan is completely digested by colonic bacteria. Colonic bacterial enzymes penetrate into matrix and degrade the matrix material and drug release ¹¹. Different enzymes such as galactomannanase, α-galactosidase, amylase, pectinase, xylanase, β-D-xylosidase, β-D-galactosidase, and Beta-D-glucosidase are present in colon  ²¹.

Conclusion

Chitosan-HCl microsphere compressed matrices provide more effective controlled release of 5-aminosalisylic acid only to the target site that is the colon having ulcerative colitis. Because the residence time of the colon is 20.9 h therefore this system gives benefits of sustained release. The absorption increases at this poor site because absorption enhancers are incorporated in the system. High gel porosity of Chitosan-HCl microsphere compressed matrices allow penetration of salts and enzymes from the colonic contents into matrix. The salts would tend to neutralize the gel pH, while the enzyme would degrade the polymer, thus increasing matrix porosity. Both processes could affect drug release. Such an influence of the matrix surrounding on drug release implies possible differences between in vitro and in vivo release from the Chitosan-HCl based matrices.

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About Authors:

Dr. Alpana Ram

Head of Department, Smt. S.L.T. Institute of Pharmaceutical Sciences, Guru GhasidasUniversity, Bilaspur (Chhattisgarh), India.

Phone Number – 07752-254350

Jitendra Kawadkar

M.Pharm (Pharmaceutics), Smt. S.L.T.Institute of Pharmaceutical Sciences, Guru Ghasidas University, Bilaspur (Chhattisgarh), India.

Cell No. 9827202304, E-mail: j_kawadkar@rediffmail.com