OBJECTIVETo prepare morphine-loaded chitosan microspheres by emulsion ionic cross-linking and investigate the effect of initial morphine quantity and different cross-linking degrees on drug loading, encapsulation efficiency and in vitro drug release.

METHODSChitosan (with a relative molecular mass of 50,000 and deacetylation degree no less than 90%) at 100 mg and morphine at 20, 30, 40, or 50 mg were dissolved by 2% acetate and dripped slowly into 15 ml soy-bean oil containing 0.75 ml Span80. After full emulsification at 35 degrees C; for 1.5 h, the mixture was dripped slowly into sodium tripolyphosphate (10 mg/ml) at the mass ratio of 5:1, 7:1, or 9:1 to allow cross-linking for 2 h. The drug loading, encapsulation efficiency and in vitro drug release of the preparations were measured.

RESULTSThe drug loading in the microsphere increased while the encapsulation efficiency reduced with the increment of the initial morphine quantity. High cross-linking degree resulted in prolonged release time of the drug loaded in the preparations.

CONCLUSIONThe microspheres loaded with morphine allows sustained release of morphine.