Percutaneous penetration of 5-methoxypsoralen in rhesus monkeys.

5-methoxypsoralen (bergapten) has been used in the treatment of psoriasis and vitiligo, and as a sun tanning accelerator. While low plasma concentrations have previously been detected, there is no data on its dermatopharmacokinetics. Three rhesus monkeys were used as a model for human skin. [14C]-5-methoxypsoralen, as a parenteral excretion control, was injected in propylene glycol with an activity of 1.12 uCi/ml at a concentration of 80 mcg/ml and urine was collected at 4, 8, 12, 24h, and then daily for a total of 6 days. [14C]-5-methoxypsoralen was then applied topically in acetone with a dose of 1.19 mc (72 mcg) and urine was collected at 4 and 24h and then daily for a total of 7 days. The amount excreted was corrected for the previously determined parenteral excretion kinetics. Intramuscular [14C]-5-methoxypsoralen had an average of 71.87±7.77% of excretion and percutaneously applied [14C]-5-methoxypsoralen had an average of 58.4±11.8% of excretion. A high percentage of the administered 5-methoxypsoralen was absorbed. This provides a foundation of methodology to evaluate the efficacy of other delivery vehicles for 5-methoxypsoralen and serves as part of its dermatotoxic profile.