Effect of preparative parameters on the characteristics of poly(D,L-lactide-co-glycolide) microspheres made by the double emulsion method

The mechanism for drug-release from poly(D,L-lactide-co-glycolide) (PLG) microspheres is generally a combination of the diffusion of the drug and the degradation rate of the polymer. The degradation rate is controlled by the molecular weight and the copolymer composition of PLG. The porosity, of the microspheres, which is dependent on the preparation method used, will also influence the drug-release rate. PLG microspheres containing mannitol(14)C were prepared by a small-scale w/o/w double emulsion method. As the PLG concentration in the middle phase was increased from 4.3 (w/w) to 43%, the entrapment efficiency of mannitol(14)C rose from 1 to 25% and the diameter of the microspheres increased from 4.5 to 29 mu m while the release rate of mannitol(14)C decreased. By increasing the volume of the internal aqueous phase the release rate of mannitol(14)C was increased. When using phosphatidylcholine (PC) as a stabiliser the size of the microspheres decreased from 23 to 16 mu m. The presence of PC during preparation lowered the entrapment efficiency of mannitol(14)C. The results were related to the dynamics of the double emulsion and the porosity of the microspheres.