Int. J. Pharm. Sci. Rev. Res., 22(2), Sep – Oct 2013; nᵒ 43, 235-239 ISSN 0976 – 044X International Journal of Pharmaceutical Sciences Review and Research Available online at www.globalresearchonline.net 235 Nargis Sultana, Fouzia Hassan, Syed Muhammad Farid Hasan*, Shuja Hasan, Fouzia Israr Ahmed, Yasir Faraz Abbasi 1 Department of Pharmaceutics, Faculty of Pharmacy, University of Karachi, Pakistan. 1 College of Pharmacy, Ziauddin University, Karachi, Pakistan. *Corresponding author’s E-mail: faridsm2002@yahoo.com Accepted on: 03-08-2013; Finalized on: 30-09-2013. ABSTRACT Dissolution, being an important process for transfer of solid substance into solution, is affected by pH changes that effects ionization of drug, consequently in-vivo behavior of the drug is altered. We investigated the effect of a slight change in pH on the dissolution behavior of erythromycin stearate tablets and its dissolution kinetics. Dissolution profiles of erythromycin tablets were later compared with some of the brands available in the local market. Six tablets of innovator product were individually tested at pH 6.8, 7.0 and 7.2 phosphate buffers using USP 28 / NF 23 (2005) guidelines. The cumulative mean dissolution behavior of innovator erythromycin stearate tablets at different pH showed that the drug release at pH 6.8 and 7.0 is almost the same at all sampling times except at 120 minutes where pH 7.0 appears to be superior as compared to pH 6.8. In case of pH 7.2, more drug was release from 15-60 minutes sampling time as compare to pHs 6.8 and 7.0 but from 90 minutes onwards up to 120 minutes, a slower drug release was obtained. Statistical analysis revealed a significant difference (α=0.05) among the dissolution profiles of erythromycin stearate innovator product in phosphate buffers (15-120 minutes) (p<0.05) but a non-significant difference were found at 60 and 75 minutes (p>0.05). It appears that higher pH might facilitate initial quicker dissolution and consequently quicker absorption and bioavailability of innovator erythromycin stearate tablets and vice versa. Dissolution data when subjected to various kinetic models, showed that the erythromycin stearate followed the Weibull model at pH 6.8 and 7.0 that indicates a linear relationship exists at these pH values between the logarithm of the dissolved amount of drug versus logarithm of time plot while the Higuchi model appears to be suitable at pH 7.2 that indicates drug release is a diffusion process at pH 7.2. Using a model independent approach, none of the selected brands showed similarity with the innovator. Close monitoring of commercial brands from time to time is thus mandatory to maintain quality of available brands. Keywords: Dissolution, erythromycin stearate, kinetics, model independent. INTRODUCTION lthough various dosage forms are available in the market, tablets share more than 80% of the market 1 . Tablets are a solid dosage form intended for oral administration of drugs. It offers numerous advantages to the manufacturer, physician, pharmacist and patient. One problem associated with a compressed tablet is that after ingestion, it must be disintegrated i-e; converted into smaller particles, and these particles should be dissolved into solution (dissolution) to be absorbed by gastrointestinal mucosa (Fig. 1). Physicochemically, “Dissolution is the process by which a solid substance enters the solvent phase to yield a solution” 3 . Dissolution plays a central role in all phases of drug development (Fig. 1). In some cases, in-vitro dissolution testing may be used in lieu of in-vivo bioequivalence studies 4 . Dissolution is a complex process and various factors affect the dissolution of drugs. These factors include: agitation, temperature, dissolution medium, pH of dissolution medium, surface tension and viscosity of the dissolution medium 5 . Since the dug is generally absorbed in a unionized form 6 , pH of the dissolution media is controlled carefully during the development of a dissolution method. The pH of the medium effects ionization of the drug which in turn affects the in-vivo behavior of the drug. “Erythromycin Stearate is the stearic acid salt of Erythromycin, with an excess of stearic acid; the percentages of erythromycin A, erythromycin B, and erythromycin C is not less than 55.0 percent, calculated on the anhydrous basis” 7 . In an acidic medium as in the stomach, erythromycin dissolution occurs rapidly, whereas in neutral or alkaline pH the drug salt is relatively stable. Consequently, erythromycin tablets are enteric coated or contained a less water-soluble erythromycin salt to protect against rapid acid dissolution in the stomach. The dissolution rate of erythromycin powder varied from 100% dissolved in 1 hour to less than 40%, depending of the pH of the medium. The slow dissolving active pharmaceutical ingredient also results in slow- dissolving drug products. Therefore, powdered raw drug material dissolution is a very useful in-vitro method for predicting the bioavailability problems of the erythromycin product in the body 8 . Erythromycin is used in the treatment of severe campylobacter enteritis, chancroid, diphtheria, legionnaires’ disease and other Legionell infections, neonatal conjunctivitis, pertussis, respiratory-tract infections, trench fever, combined with neomycin, for the prophylaxis of surgical infection in patients undergoing bowel surgery etc 9 . Effect of pH on the Dissolution of Erythromycin Stearate Tablets Available in Local Market A Research Article