Rifampicin Carrying Poly (D, L‐Lactide)/Poly(Ethylene Glycol) Microspheres: Loading and Release

The aim of this study is to prepare rifampicin-loaded poly (D,L-lactide)/poly(ethylene golycol) (PDLLA/ PEG) copolymer microspheres as an injectable drug delivery system. PDLLA homopolymers with three different molecular weights (9,760, 14,540, and 23,050 daltons) were synthesized and then transesterified with PEG (with a molecular weight of approximately 3,300-4,000 daltons). By changing the ratio of PEG to PDLLA, block copolymers with different chain structures were synthesized. PDLLA and PDLLA/PEG microspheres in the size range of 2-10 microns were prepared by a modified solvent evaporation technique with the use of methylene chloride as the solvent and methyl cellulose as the emulsifier within the aqueous dispersion medium. Rifampicin was loaded within the microspheres during particle formation. Effects of the solvent/polymer and drug/polymer ratios, PDLLA molecular weight, and PEG content on drug loading and release were investigated. High drug loadings up to 100 mg rifampicin/g polymer were achieved. Both size and drug loadings were decreased by an increase in the solvent/polymer ratio and PEG content and by a decrease in the drug/polymer ratio and PDLLA molecular weight. High release rates were observed in the first 5 days after which constant and slow release rates were noted. Drug release was decreased by a decrease in the solvent/polymer ratio and PEG content and by an increase in the drug/polymer ratio and PDLLA molecular weight.