Endocrine Abstracts (2007) 13 P269

What factors influence serum testosterone levels when initiating Nebido®?

Robert Moisey, Julie Swinburne & Steve Orme

Leeds Teaching Hospitals NHS Trust, Leeds, West Yorks, United Kingdom.

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 manufacturer’s 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 chromatography–tandem mass spectrometry) and SHBG were measured.

The mean (range) age at baseline was 49.4 yrs (20–78). 31 (86%) had received prior treatment with another testosterone preparation. Baseline serum T was 11.0 nmol/L (0.3–54.8), [reference range 8.0-30.0] rising to 18.5 nmol/L (6.2–32.8) 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 (130.0–152.0, RR 13-71) vs. 31.0 (9.0–82.0), 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 (11.7–32.8) vs. 16.2 nmol/L (6.2–32.6), P=0.009)] and higher SHBG [42.3 nmol/L (11.0–82.0) vs. 25.4 nmol/L (9.0–57.0), P=0.003].

Conclusion: In this study the manufacturer’s 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.

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