Comparison of physical properties and drug-releasing characteristics of white petrolatums.

White petrolatums of Japanese Pharmacopoeia grade and Sun white ® marketed as a cosmetic were characterized by measuring their physical properties and drug-releasing characteristics. White petrolatums of Japanese Pharmacopoeia grade available commercially in Japan were Perfecta, White 1 S, Ultima, Snow, Snow V and Regent (Propeto ® ). Penetrating stress, shear stress and spreading properties were measured as physical properties of the white petrolatums. The physical properties of white petrolatums varied, and Regent was the softest and the most spreadable ointment base. In vitro release test was performed using flow-through Franz diffusion cells. Fluorescein isothiocyanate and tetracycline hydrochloride were used as drug models. Their release characteristics varied among the tested white petrolatums, and Regent had the best release properties. Among the white petrolatums, with the exception of Regent, the release properties should depend on the distribution of drugs between white petrolatum and the receiver solution. Considerations of usability and characteristics of the principal agent are needed when choosing white petrolatums.