Comparability of Single Measurements of Serum Testosterone to the 24‐Hour Cavg in Patients Using Testosterone 2% Solution

IntroductionEfficacy of testosterone replacement therapy is determined by the proportion of men with 24‐hour average serum testosterone concentration (Cavg) in the normal range. In clinical practice, monitoring and dose adjustments are based on single testosterone measurements; however, how single measurements reflect Cavg is unclear.AimThis post‐hoc analysis evaluated whether single serum testosterone measurements and Cavg from the same day are both in the normal range in men receiving testosterone replacement therapy.MethodsIn an open‐label, multicenter, titration trial, androgen‐deficient men (N = 155) were started on 60‐mg daily morning dose of testosterone 2% solution (Axiron®, Eli Lilly and Company, Indianapolis, Indiana, USA) applied to axillae (30 mg/axilla). Serum testosterone Cavg was determined on Days 15, 60, and 120. If necessary, dose was adjusted to maintain Cavg in the normal range (300–1,050 ng/dL). This analysis included subjects (n = 105) whose Cavg was within the normal range on Days 15, 60, and 120.Main Outcome MeasuresProportion of men with normal serum testosterone levels at 2, 4, or 8 hours post‐dose on Days 15, 60, and 120.ResultsGreater than 93% of subjects had testosterone serum levels within the normal range 2, 4, or 8 hours post‐dose on at least 1 day. In subjects with blood samples available from Days 15 and 60 or Days 15 and 120, 71.1% to 79.8% had normal levels at 2, 4, or 8 hours post‐dose on both days, and in subjects with blood samples available from Days 15, 60, and 120, 63.9% to 68.8% had normal levels at 2, 4, or 8 hours post‐application on all 3 days.ConclusionLess than 70% of single testosterone measurements made on 3 separate days were concordant with same‐day Cavg for all 3 days. These findings, which are specific for testosterone 2% solution, indicate that single measurements do not always reflect the 24‐hour Cavg, and may possibly lead to inappropriate dose adjustments. Muram D and Baygani S. Comparability of single measurements of serum testosterone to the 24‐hour Cavg in patients using testosterone 2% solution. J Sex Med 2014;11:2826–2829.