Monitoring testosterone replacement therapy with transdermal gel: when and how?
Testosterone replacement therapy (TRT) is recommended for the treatment of most cases of male hypogonadism. Transdermal testosterone (T) gels are commonly used in clinical practice; however, there is little evidence concerning how to monitor dosage to bring and maintain serum T levels in the normal physiologic range.
We examined 30 hypogonadal patients undergoing treatment with 40 mg/day transdermal 2% testosterone gel. After a week from treatment onset, all patients underwent a total of four measurements to assess serum total T, bioavailable T and free T at + 2 h (samples A and A′) and + 23 h (samples B and B′).
No significant difference was found concerning total, free and bioavailable T between the two samples taken at the same time points (A vs A′ and B vs B′). A repeated-measures mixed effects regression model showed significantly lower serum levels of total, free and bioavailable T at + 23 h compared to + 2 h (total T, β = − 3.050 ± 0.704, p < 0.001; free T, β = − 85.187 ± 22.746, p < 0.001; bioavailable T, β = − 1.519 ± 0.497, p = 0.003) without a significant between-sample variability. Serum T > 3.5 ng/ml at + 2 h was reached in 21/30 patients (70%), but only 11 (36.7%) still had adequate serum T at + 23 h.
Assessment of TRT with transdermal gels at its peak and at its minimum could be useful in providing a finely tailored treatment for hypogonadal men, both preventing supra-physiological levels and maintaining adequate concentrations through the day.
KeywordsTestosterone replacement therapy Monitoring Male hypogonadism Testosterone gel
Compliance with ethical standards
Conflict of interest
On behalf of all authors, the corresponding author states that there is no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional ethics committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
All patients provided written informed consent for their participation.
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