Metformin Hydrochloride Microparticles for Oral Controlled Release: Effect of Formulation Variables*

Objectives: The aim of the present study was to evaluate effects of various polymers on the release of a water soluble drug by using spray drying technique of microencapsulation. Methods: Spray drying is a single step technique, less time is required and loading efficiency is not affected by the nature of the drug whether hydrophilic or hydrophobic. Eudragit RS 30D, RL 30D and Ethylcellulose (Surelease) were chosen as rate controlling polymers. Various drug to polymer ratios used were 1:1, 1:2, 1:3, 1:5, 1:7, 1:9 and 1:11. The microparticles were characterized by encapsulation efficiency, particle size, powder x-ray diffraction, DSC, scanning electron microscopy, and in-vitro drug release. Results: No drug excipient interaction was observed in DSC studies. The maximum control of the drug release was observed at the lowest drug to polymer ration i.e. 1:11. Since the drug is freely soluble in water it was difficult to control its release. Among the three polymeric dispersions used, Eudragit RS 30D exhibited better control on the release of drugs. Powder X-ray diffraction studies revealed that there is no conversion of the drug from its original crystalline state to amorphous state after the spray drying process. Conclusion: Spray drying can be used as a method for the formulation of controlled release drug delivery systems. Eudragit RS 30D showed better control over drug release, this may be due to less penetration of water within the microparticles.