Preservative activity and in vivo percutaneous penetration of butylparaben entrapped in liposomes.

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Abstract
Butylparaben (BP) was added to liposomes prepared by the hydration method from egg phosphatidylcholine (egg PC), cholesterol, and dicetylphosphate in a molar ratio of 4:2:1 for the purpose of antimicrobial preservation. Most of the BP was entrapped in liposomes near the polar surface of the lipid bilayers, and rapid equilibrium was observed in its distribution between liposomes and the outer aqueous phase. The antimicrobial activities of liposomes containing BP were studied qualitatively against eight kinds of microorganisms. Although the liposome suspension without BP (empty liposomes)had no effect on the microorganisms, liposome suspensions with BP showed antimicrobial activities. The preservative effect was roughly proportional to the free concentration (not the total concentration) of BP. Percutaneous penetration of liposomes containing BP after topical application was studied in vivo in guinea pigs by autoradiography. 14C-BP in liposomes was observed to penetrate into the body, but no difference was found in its distribution pattern in comparison with that after administration as an ointment. On the other hand, 14C-dipalmitoylphosphatidylcholine, a marker of egg PC, remained on the skin surface and was scarcely detected in the body, suggesting that the percutaneous penetration of liposomes themselves did not occur.