Influence of Drug/Polymer Ratio on the Encapsulation Efficiency of Highly Hydrophilic Drug

Abstract

Microencapsulation of drugs into solid non-biodegradable polymeric microspheres by solvent evaporation technique remains challenging especially with those having low molecular weight and high hydrophilicity nature. This paper presents an efficient encapsulation protocol for this group of drugs, demonstrated using losartan potassium as a model compound which is encapsulated into Eudragit RS 100 (ERS) and Eudragit RL 100 (ERL) microspheres. The microspheres were prepared using solvent evaporation technique with an ultimate aim of prolonging drug release. Six formulations were prepared using different drug/polymer ratio. The effects of polymer type and polymer/ drug ratios on the size, surface morphology, encapsulation efficiency and the release characteristics of the microspheres were examined. The formulation containing drug/polymer ratio 1:5 in which the ratio between the two polymers (ERS:ERL) is 4:1 was found to be the most appropriate with respect to encapsulation efficiency (94.43 % ± 0.277), drug loading (19.58 % ± 0.417), batch yield (80.40 % ± 1.712), particle size (204.23 ± 8.438) and having highest corelation coefficient (0.9829) amongst all formulation thus providing a desired drug release characteristics. At the optimum stirring speed of 750 rpm, best spherical shaped particles with good surface characteristics were obtained, which were distributed over the size range of 120-270 μm. This proposed method has been successfully used to prepare batches of microspheres having high encapsulation efficiencies.