In vivo human transfer of topical bioactive drug between individuals: estradiol

This study determined the in vivo human bioavailability of topical estradiol, and the transfer of drug between dosed subject and naive recipient. In vivo bioavailability was determined in human volunteers by (14)C urinary excretion following topical [(14)C]-estradiol (0.06%) dose administration and were adjusted by intravenous human excretion amounts to give absolute bioavailability amounts. Drug transfer was determined by volunteer skin contact/rubbing for 15 minutes, 1 hour after topical dosing. [(14)C]-estradiol bioavailability as percent dose absorbed (n=6) was 7.5+/-4.1 from protected dose site, 8.2+/-6.3 from non-protected dose site, 6.6+/-7.6 from dosed volunteers subjected to skin contact/rub and 4.3+/-3.8 from non-dosed volunteers subjected to skin contact/rub. Between these small groups, the values were not statistically different. Under experimental conditions, a measurable dose of radioactive 17beta-estradiol dose was delivered to naive recipient volunteers through skin contact/rub with other volunteers previously topically dosed. Any residual topical bioactive chemical which resides on the open skin surface can transfer by skin contact to another individual. It is important for prescribing physicians and patients to understand that clinically significant transfer of topical bioactive drugs can occur. This may be particularly important for substances which may produce inadvertent effects.