Study on release of recombinant human growth hormone poly lactice-co-glytic acid microspheres in vitro and the effects of additives

OBJECTIVE To study the release of recombinant human growth hormone contained in poly lactic-co-glycolic acid (PLGA) microspheres in vitro and the influence of additives on the drug release. METHODS Some parameters affecting the drug release during 34 days were assessed using native size exclusion chromatographic methods, including replacememt of the methylene chloride with ethyl acetate as organic solvent, lactide/glycolide ratios in PLGA, addition of salts to the external aqueous phase, presence or absence of emulsifier in primary W/ O emulsion and Different amout of drug input.RESULT There is no effect on the drug-release of rhGH-PLGA microspheres using methylene chloride or ethyl acetate as organic solvent. Different lactide/glycolide ratio of PLGA, especially lactide: glycolide=75:25 showed much more amount of cumulative release. Addition of salts to external aqueous phase or addition of emulsifier in primary W/O emulsion made the cumulative release low. And adding more amount of drug made the cumulative release high. CONCLUSION rhGH-PLGA microspheres showed evident sustained release effect. The rate of release appeared to depend on the five parameters mentioned above.