Background: A variety of preparations for testosterone replacement therapy are currently available. Testogel, a transdermal gel, is widely used and considered one of the most convenient. Measurement of serum testosterone level at various times after application of the gel is regarded as one of the ways of monitoring response to treatment.
Aim: To investigate the variability of testosterone absorption and whether testosterone levels prior to application of the gel and 2 hours later can be a useful marker for checking testosterone replacement.
Subjects and methods: Twelve patients aged between 34 and 67 years (median age, 54.5) with hypogonadism, regularly followed up in our Department by the testosterone specialist nurse, were studied. They were all using Testogel transdermal gel, 50 mg daily. Blood samples were taken (2224 hours following previous days gel application) between 0900hrs and 1000hrs prior to the gel being applied (time 0) and then 2hrs after application of the gel (time 120). Gel was applied to either top of arm or back of shoulder. BMI measurement was recorded.
Results: Median serum testosterone at time 0 was 12.7 nmol/L (range 3.626.1) and at time 120 was 16.6 nmol/l (range 532.9). The median increment was 4.75 (range 116.9). There was correlation between serum testosterone at time 0 and 120 (r=0.7; P<0.05) and a significant difference between serum testosterone at 0 and 120 for each patient (P=0.04). There was no correlation between serum testosterone at time 0 and the increment of serum testosterone. There was no clear correlation between the increment and the BMI measurement.
Conclusion: There is a wide variation in increment serum testosterone two hours after application of Testogel. This highlights the importance of timing of testosterone samples and the importance of using basal samples to monitor therapy.