Partition Characteristics and Retention of Anti-inflammatory Steroids in Liposomal Ophthalmic Preparations

Abstract

Liposome preparations containing dexamethasone or its ester derivatives were formulated as eye drops. Steroids were efficiently incorporated into the liposomes; the incorporation ratio was not affected by the period of sonication or the addition of stearylamine or dicetylphosphate, but was decreased by the addition of cholesterol. The incorporation ratio appears to be governed by partition equilibrium between the lipid membrane and the aqueous phase. A theoretical interpretation of the findings was attempted by using partition theory. No release of dexamethasone palmitate from liposomes was detected, but a small portion of other steroids was rapidly released when the liposome preparation was diluted with a buffer solution. The amount of steroid released from the liposomes may also be governed by the partition equilibrium.