ABSTRACT This investigation is to find a prolonged or delayed For this, 50 mg of pectin microspheres were dispersed into 10 ml of coating solution which was prepared by dissolving 500 mg of ES100 in ethanol and acetone in the ratio of 2:1. This organic phase was then poured into 50 ml of light liquid paraffin containing 2% (w/v) of Span 85. This was maintained under agitation (2000 rpm) at room temperature for 3 h to allow solvent evaporation. Microspheres were then collected by filtration and washed with n-hexane to remove excess liquid paraffin and were redispersed in distilled water followed by lyophilization Samples were ground with KBr and compressed to make pellets. The following samples were assayed: (A) lamivudine, (B) empty eudragit-coated pectin microspheres, (C) physical mixture of pectin, eudragit S-100, and lamivudine, and (D) lamivudine loaded microspheres. 2.2.5 Differential scanning calorimetry (DSC) Differential scanning calorimetry (DSC) measurements were performed with a DSC 6200 thermal analysis system (Seiko Instruments Inc., Tokyo, Japan). Samples (4 mg) were heated from 25 to 200 °C in sealed aluminium pans at a scanning rate of 10 °C/min under nitrogen purge with an empty aluminium pan as reference. 2.2.6 Determination of entrapment efficiency The drug loaded microspheres (100 mg) were powdered and suspended in 100 ml of acetone-ethanol mixture and 6 ml of acetonitrile was added and vortexed for 5 min. The drug content was determined by measuring the absorbance at 261 nm using UV-Vis spectrophotometer (Shimadzu, UV-Vis 1700, Japan). The drug entrapment efficiency was calculated using the following equation: All the formulations were analysed in triplicate (n =
