Effects of formulation factors on physical properties and in vitro biological activity of propylthiouracil liposomes

Abstract

Propylthiouracil (PTU) was encapsulated in reverse phase evaporation liposomes for the purpose of topical treatment of psoriasis. PTU partitioning between the liposomal bilayer and the aqueous phase depended on lipid concentration when the liposomal system was not saturated with PTU. In the system with saturation of PTU, on the other hand, lipid concentration did not affect PTU encapsulation. The PTU-saturated system also gave the highest encapsulation efficiency. Surface charge, pH, and cholesterol content had interaction effects on PTU encapsulation. With respect to liposomal charge, negative iiposomes at pH 7.4, neutral liposomes at pH 7.4, and positive liposomes at pH 9.0, without cholesterol, gave the highest encapsulation efficiency. The presence of cholesterol in liposomes decreased encapsulation efficiency. Liposomal formulations provided sustained release of PTU as well as retarded dehydration. Both free PTU and PTU liposomes could inhibit BALB/c 3T3 mouse fibroblast proliferation to a similar degree. However, PTU liposomes showed the sustained release characteristic. PTU liposomes were physically stable for at least 8 weeks when stored in a refrigerator (4-8 .C).