A method using biodegradable polylactides/polyethylene glycol for drug release with reduced initial burst.

Post-coating of biodegradable polylactides (PLA)/polyethylene glycol (PEG) microspheres with a gelatin film produced by dipping the microspheres into a gelatin solution to reduce the initial drug release burst was investigated. Biodegradable block PLA/PEG microspheres, prepared by w/o emulsion/solvent evaporation, showed that the hydrophilic segment PEG protruded to the sphere surface. However, these microspheres also showed a large burst release in the initial period. Post-coating of the PLA/PEG microspheres with a gelatin film by dipping the microspheres into a dilute gelatin solution effectively inhibited the initial burst release rate in the drug release tests. Post-coating of gelatin reduced 98% of the burst release. With thicker coatings, there were slower releasing rates, and the release rate can be simply related to the coating thickness.