It is important when initiating intramuscular Nebido (testosterone undecanoate) to monitor the serum testosterone level to ensure physiological replacement is achieved. Following a loading regimen of Nebido the manufacturer recommends measuring testosterone levels to determine the frequency of subsequent injections.
We conducted a retrospective study of 36 hypogonadal men [12 (33%) primary hypogonadism, 24 (67%) secondary hypogonadism] to establish what factors may influence the level of testosterone after initiating Nebido. Following the manufacturers guidelines subjects had an IM injection of 1000 mg Nebido at week 0 and 6. At week 18, prior to the third injection, the serum testosterone (serum T) (assay: stable-isotope dilution liquid chromatographytandem mass spectrometry) and SHBG were measured.
The mean (range) age at baseline was 49.4 yrs (2078). 31 (86%) had received prior treatment with another testosterone preparation. Baseline serum T was 11.0 nmol/L (0.354.8), [reference range 8.0-30.0] rising to 18.5 nmol/L (6.232.8) by week 18 (P=0.001). 28 (77.7%) were within our local reference range. Serum SHBG did not change significantly [38.8 nmol/L (130.0152.0, RR 13-71) vs. 31.0 (9.082.0), P=0.16].
At week 18 the serum T correlated positively with age (r=0.46, P=0.01) and negatively with weight (r=−0.38, P<0.05), BMI (r=−0.40, P<0.05) and body surface area (BSA) (r=−0.36, P<0.05). Patients with primary hypogonadism had higher testosterone levels [23.2 nmol/L (11.732.8) vs. 16.2 nmol/L (6.232.6), P=0.009)] and higher SHBG [42.3 nmol/L (11.082.0) vs. 25.4 nmol/L (9.057.0), P=0.003].
Conclusion: In this study the manufacturers guidelines for commencing Nebido provided 78% of men with levels of testosterone within the reference range. Older men and those with lower weight, BMI or BSA tended to have higher levels of testosterone.