Characteristics of liposome ointments in drug stability and topical drug delivery

Abstract

Various dermatological samples containing liposomes as a drug carrier were prepared, and their effects on drug stability and characteristics for effective topical drug delivery were investigated. Hydrocortisone-21-acetate, an antiinflammatory agent, was used as the model drug. Being hydrophobic and water-degradable, hydrocortisone acetate was first expected to be unstable in liposomes. However, upon encapsulation in liposomes by the precipitation method, the drug particles were found to be entrapped in the liposomes, as a solid core surrounded by a multilamellar lipid membrane in each vesicle. This structure seemed to have protective effects on the drug by minimizing the amount of water available around the drug particles and reducing the chances of water-induced degradation reactions. Three types of ointment bases, namely hydrogel, cream, and poly(ethylene glycol) ointment, were prepared, and variations in the ointment formulations were made for the study of the effects of liposomal encapsulation, base materials, and the purity of lipid products on the stability of hydrocortisone acetate. It was found that liposomally encapsulated drug was more stable than free-form drug in an ointment sample. Also, the hydrogel base was found to be the most effective for the drug stability among the three types of bases in spite of its high water content. Moreover, the high viscosity of the hydrogel base seemed to have contributed to the maintaining of the drug stability. It was also found that the lipid product of higher purity provided better effects on the drug stability. The liposomal hydrogel ointment was found to be advantageous in topical drug delivery from an in vitro test of drug permeation through the pig ear skin and a test of drug release into an aqueous medium. The amount of hydrocortisone acetate that had permeated through the skin membrane in the test was found to be three times less in the case of liposomal hydrogel than in the case of free-drug hydrogel. H...