Endocrine Abstracts

Objective: To identify the optimal regime for physiological replacement in hypogonadism. We assessed the pharmacokinetics of 3 different dose-intervals for i.m. administration of the new parenteral formulation of testosterone undecanoate in castor oil (Schering AG Berlin).

Methods: Ten hypogonadal subjects (primary n equals 4 or secondary n equals 6) with a baseline T at diagnosis of less than 7 nanomols per litre were recruited and randomly allocated into the 3 treatment regimens. Current androgen replacement was stopped for 6-9 weeks prior to entering the treatment phase (36 weeks) of the study. Subjects were randomised into one of three groups receiving TU 500 milligrams every 6 weeks, 750 milligrams every 9 weeks and 1000 milligrams every 12 weeks. T measurements (nanomols per litre) were carried out at baseline and then at 3 weekly intervals. In addition T was also measured on days 4, 7, 10 and 14 following the first and last TU dose.

Results: Ten subjects (38.3 plus/minus 2.43 years) to date have been randomised into the study. First dose Cmax was as follows: 3.0 plus/minus 0.6 to 21.4 plus/minus 1.8 in the 500 milligram group, 10.8 plus/minus 1.5 to 47.1 plus/minus 18.9 in the 750 milligram group and 1.6 plus/minus 0.8 to 34.7 plus/minus 12.1 in the 1000 milligram group (mean plus/minus SEM). The mean T concentrations post first dose were 13.2 plus/minus 1.4, 22.9 plus/minus 3.5 and 19.4 plus/minus 2.8 for the 500, 750 and 1000 milligram groups respectively. Final dose Cmax was 28.8 plus/minus 3.9, 73.4 plus/minus 20.3 and 44.2 plus/minus 5.5 with post last dose mean T concentrations of 22 plus/minus 1.6, 35.7 plus/minus 14.6 and 27.7 plus/minus 1.9 in the 500, 750 and 1000 milligram groups respectively.

Conclusion: Supraphysiological excursions of peak T levels were dose (1000 and 750 milligram only) related. TU 500 milligrams per 6 weeks provided the most physiological androgen replacement with T values within the normal range at all time points.