Thesis (M.Sc. in Pharm.)--Chulalongkorn University, 2000

The present study was designed to develop sustained release microcapsules of andrographis paniculata nees extract via the oil in oil solvent evaporation technique. Effect of process and formulation factors on microencapsulation and release characteristics were investigated. As the stirring rate increased from 250 to 1200 rpm, the microcapsule size decreased, whereas the rate at 1000 rpm gave the most appropriate yield, highest drug content and core entrapment and highest release rate constant at pH 6.8. Among the emulsifier concentration of 0-2.0%, the 0.5% Span 80 gave appropriate size, highest drug content and core entrapment. At pH 1.2, the 0.5% Span80 showed the significantly higher release rate constant and dissolution efficiency. The 1:2 core to wall ratio gave the highest core entrapment, whereas the 1:1 ratio showed the highest yield and drug content. The particle size of microcapsules from 2:3 ratio was markedly large due to the high concentration of the internal phase. Eudragit RL100 was superior to Eudragit RS100 as it gave the higher yield, smaller size, higher core entrapment and superior release rate constant and dissolution efficiency. Addition of poloxamer 188 of 20%, inspite of a slight decrease of core entrapment and particle agglomeration, gave superior release rate constant and dissolution efficiency to those without Poloxamer 188. The release mechanism of andrographolide from microcapsules was demonstrated to follow diffusion-controlled model.