The work investigates the effect of various formulation variables like drug-polymer ratio, stirring speed, and surfactant (Span 80) concentration on the properties of ethyl cellulose microparticles containing metformin HCl, prepared by emulsification solvent evaporation technique. The drug entrapment efficiency, particle size, and drug release behaviour of these microparticles were influenced by these formulation variables. The sustained release characteristic of these microparticles was more prominent in pH 6.8 than pH 1.2. The drug release from ethyl cellulose microparticles was found to follow the Fickian (diffusion-controlled) release mechanism. The drug-polymer interaction and surface topography of these microparticles were analyzed by FTIR spectroscopy and SEM, respectively. 1. Introduction Metformin HCl is a biguanide antihyperglycemic drug, which is orally used in the management of noninsulin-dependent diabetes mellitus (NIDDM or Type II diabetes mellitus) alone or in combination with other hypoglycemics [1, 2]. Its antihyperglycemic effect is due to the metabolic activities at several sites (biophase), including liver, intestinal muscle cells, and adipocytes [3]. Metformin also has beneficial effect on several cardiovascular risk factors such as dyslipidemia, elevated plasma-plasminogen activator inhibitor, other fibrinolytic abnormalities and insulin resistance [4]. It has a short biological half-life of 1.5–1.6？h and the daily requirement of it is 1.5–3？g/day [5, 6]. Therefore, the marketed immediate release product needs to be administered 2-3 times daily to maintain effective plasma concentration [7]. Henceforth, there being high incidence of gastrointestinal side effects and toxicity. These drawbacks can be overcome by designing suitable sustained release metformin HCl formulations. Administration of a sustained metformin HCl release dosage form could reduce the dosing frequency and improve the patient compliance. Among various oral sustained drug delivery systems, polymeric microparticles are one of the options and have been studied in past few decades in order to deliver drug molecules to the target site with specificity with several advantages like better oral bioavailability of drugs, reduction in side effects, decreased dosing frequency, and hence, improved patient compliance [8–10]. Microparticles are solid particles ranging in size from 1 to 1000？μm. In general, polymeric microparticles consist of polymeric matrix, in which drug molecules are dispersed, entrapped, or adsorbed. A number of different polymers both biodegradable and
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