Reduction in 24-hour plasma testosterone levels in subjects who showered 15 or 30 minutes after application of testosterone gel.

STUDY OBJECTIVE

To investigate whether showering, to prevent the involuntary transfer of testosterone to others through skin contact, either 15 or 30 minutes after application of testosterone gel would significantly affect plasma testosterone levels.

DESIGN

Prospective 3-way crossover trial.

SETTING

University hospital in the Netherlands.

SUBJECTS

Ten agonadal female-to-male transsexuals who had sex-reassignment surgery at least 3 months earlier.

INTERVENTION

Subjects were randomized to one of three application regimens for testosterone gel 50 mg/day, each lasting 7 days: testosterone application after showering (standard regimen), shower was taken 30 minutes after testosterone application, or shower was taken 15 minutes after testosterone application. Subjects then crossed over to each of the other two application regimens for a total of 21 days of study participation.

MEASUREMENTS AND MAIN RESULTS

On day 7 of each application regimen, mean plasma testosterone levels were determined before testosterone application and at 1, 4, 7, and 10 hours after application. With the standard regimen, mean plasma testosterone levels at all time points after application were in the normal range: mean ± SD average concentration 994 ± 1026 ng/dl. When a shower was taken 30 or 15 minutes after application, plasma testosterone levels at 1, 4, 7, and 10 hours were significantly lower: mean ± SD average concentration 401 ± 231 ng/dl for 30 minutes after application (p<0.01) and 320 ± 248 ng/dl for 15 minutes after application (p<0.01).

CONCLUSION

Showering within 30 minutes after application of testosterone gel 50 mg/day reduces absorption of testosterone and results in unacceptably low plasma testosterone levels in most users. Therefore, this strategy cannot be recommended to prevent involuntary transfer of testosterone.