Endocrine Abstracts

Background: Many testosterone (T) formulations are now available for treating male hypogonadism. Intramuscular injectable T esters and transdermal T gel are the most commonly used in clinical practice. Transdermal T gel is often preferred by patients due to ease of use and reduced fluctuations in serum T compared to injectable esters. A daily dosage of 20 mg – 80 mg mimicking circadian profile is recommended to adequately treat hypogonadal men.

Aim: There is conflicting evidence concerning intraindividual variability in serum T level after T gel administration. We aim to evaluate serum T level two hours and twenty-three hours after gel admnistration

Materials and Methods: Thirty-one male long-term hypogonadal patients were asked to apply 2 g of T gel (40 mg) in the morning to the upper arms/shoulders. Two blood samples were collected 2 hours after gel administration at peak serum T (T+2) seven days apart. Subsequently, two blood samples were collected twenty-three hours after gel administration at nadir serum T seven days apart (T+23).

Results: No significant difference in serum T was observed between the two samples taken at T+2 (8.15±8.24 vs 8.06±7.09 ng/ml, P=0.818) and T+23 (3.41±2.45 vs 2.91±1.87 ng/ml, P=0.226). Furthermore, as expected, a significant positive correlation between the two samples was found for serum T at T+2 (r=0.973, P=0.001) as well as at T+23 (r=0.482, P=0.006). Otherwise, average T values at T+2 and T+23 are significantly different (8.11±7.61 vs 3.19±1.90 ng/ml) and do not correlate significantly (r=0.062, P=0.747). At T+23, 13 men (41.94%) showed serum T greater than 3.46 ng/ml, 14 (45.16%) showed serum T values below 2.31 ng/ml and 4 (12.9%) had serum T values in the ‘grey zone’.

Discussion: T gel administration is not affected by day-to-day intraindividual variability when T is measured both at peak and at nadir. This data permits to avoid frequent blood samples to evaluate serum T response to gel administration. The lack of correlation between T+2 and T+23 shows that it is not advisable to estimate T peak level considering T nadir level. A measurement of T level both at its peak and at its nadir is suggested to evaluate T gel therapy. Finally, 40 mg T gel may not be enough to reach T reference range in all subjects undergoing treatment.