Efficacy of a sunscreen containing butyl methoxydibenzoylmethane against ultraviolet A radiation in photosensitized subjects.

Topical formulations containing a new chemical entity, the ultraviolet A absorber Parsol 1789 (butyl methoxydibenzoylmethane), were evaluated as agents for protecting human skin against ultraviolet A (UVA) radiation. Healthy subjects were photosensitized to UVA radiation by ingestion of 8-methoxypsoralen (0.6 mg/kg). After 90 minutes, five formulations (vehicle, vehicle + butyl methoxydibenzoylmethane, vehicle + butyl methoxydibenzoylmethane + padimate O, vehicle + padimate O, and a marketed sunscreen containing padimate O, oxybenzone, and octyl salicylate) were applied in a randomized, double-blind manner to areas on the lower part of the back. Thirty minutes later, sites in the five treated areas and in a sixth unprotected area were exposed to graduated doses of UVA radiation. Test sites were evaluated for erythema 48 and 72 hours after UVA exposure, and for melanogenesis approximately 2 weeks later. The combination of butyl methoxydibenzoylmethane + padimate O demonstrated significantly greater protection than the combination of padimate O, oxybenzone, and octyl salicylate.