Transfer of transdermally applied testosterone to clothing: A comparison of a testosterone patch versus a testosterone gel

Aim. To assess the amount of testosterone transferred from the abdominal application sites of a transdermal testosterone patch and a transdermal testosterone gel to cotton T-shirts worn for 24 hours during each treatment. Methods. During a crossover study comparing the pharmacokinetics of a testosterone patch versus a testosterone gel in 28 hypogonadal men, subjects wore fresh cotton T-shirts for 24 hours on the seventh and fourteenth days of each treatment and during a 24-hour baseline period. At the end of each evaluation, the abdominal section of the shirt was carefully cut out, extracted in alcohol, and analyzed for testosterone by a direct radioimmunoassay. The minimum quantifiable amount of testosterone was 0.03 mu g per T-shirt sample. Results. The median amounts of extracted testosterone were 0.44 mu g for the baseline samples, 25.4 mu g for the average of the two patch samples, and 6,762.7 mu g for the average of the two gel samples (all comparisons P < 0.0001). Significant correlations were observed between the day 7 and day 14 data for both the patch (R = 0.4982. P < 0.01) and the gel (R = 0.8383; P < 0.0001). No significant correlations were found between the baseline, patch, or gel data, or between these and any demographic or pharmacokinetic parameters. A quantitative interpretation of the findings suggests that the baseline results are consistent with the transfer of testosterone in sweat; the patch results are probably due to the transfer of a small amount of residual testosterone left on the abdominal skin from the prior day's patches; and the gel results reflect die desquamation of stratum corneum containing a portion of the abdominally applied testosterone. Conclusions. There are large differences in the amount of testosterone that can be transferred from the application sites of transdermal patches and gels. The latter should be covered with clothing to minimize transfer through intimate skin-to-skin contact.