Objective: To evaluate the utility of single serum testosterone measurement in patients receiving transdermal testosterone therapy.
Research design and methods: Data were from an open-label, 120 day, multi-center titration trial in androgen-deficient men receiving an initial daily dose of 60 mg testosterone (testosterone topical solution 2%) applied to axillae (30 mg/axilla). Average concentration (Cavg) of serum testosterone (TT) was determined on days 15, 60, and 120; doses were adjusted to maintain normal Cavg (300-1050 ng/dL [10.4-36.4 nmol/L]). Accuracy of single serum TT measurements (2, 4, 8, 12, 16, and 20 hours post-dose) was assessed in patients with Cavg TT within and below (<300 ng/dL [<10.4 nmol/L]) the normal range.
Clinical trial registration: Clinicaltrials.gov - NCT00702650.
Main outcome measure: Serum testosterone levels.
Results: In patients with normal Cavg (n = 85), 79% to 92% had serum testosterone levels within normal range 2, 4, 8, 12, 16, and 20 hours post-dose; significant effects of time post-dose for single testosterone measurement accuracy (P = 0.01) were observed: testing accuracy peaked 4-8 hours post-dose and tapered ∼16 hours post-dose. In 28/63 instances with low Cavg TT throughout the study a normal 2 hour serum TT level was observed. The average percentage (across all days) of discordant results between Cavg (<300 ng/dL [<10.4 nmol/L]) and single serum TT measurements (300-1050 ng/dL [10.4-36.4 nmol/L]) declined with increasing time from dose application (44% at 2 hours, 38% at 4 hours, 22% at 8 hours, 3% at 16 hours).
Conclusions: Reliance on a single serum testosterone measurement to determine the need for dose adjustment of testosterone topical solution 2% may lead clinicians to change the dose unnecessarily, or alternatively, not increase the dose when necessary. The results reported here are limited to testosterone topical solution 2% and may not be applicable to other topical agents.
Keywords: Absorption; Accuracy; Hypogonadism; Testosterone; Topical administration; Transdermal administration.