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Intramuscular Testosterone Undecanoate: Pharmacokinetic Aspects of a Novel Testosterone Formulation during Long-Term Treatment of Men with Hypogonadism

Klinik II und Poliklinik für Innere Medizin der Universität zu Köln (M.S., T.M., A.C., W.K.), 50931 Köln, Germany; Jenapharm GmbH & Co. KG (D.H., D.R., M.O., M.E., U.M.), 07745 Jena, Germany; and Evangelisches Krankenhaus Herne (F.J.), 44623 Herne, Germany

Address all correspondence and requests for reprints to: Friedrich Jockenhövel, M.D., Evangelisches Krankenhaus Herne, Wiescherstraße 24, 44623 Herne, Germany. E-mail: f.jockenhoevel{at}evk-herne.de.

In an open-label, randomized, prospective trial, we investigated pharmacokinetics and several efficacy and safety parameters of a novel, long-acting testosterone (T) undecanoate (TU) formulation in 40 hypogonadal men (serum testosterone concentrations < 5 nmol/liter). For the first 30 wk (comparative study), the patients were randomly assigned to receive either 10 x 250 mg T enanthate (TE) im every 3 wk (n = 20) or 3 x 1000 mg TU im every 6 wk (loading dose) followed by 1 x 1000 mg after an additional 9 wk (n = 20). In a follow-up study, observation continued in those patients who completed the comparative part and opted for TU treatment (8 x 1000 mg TU every 12 wk in former TU patients and 2 x 1000 mg TU every 8 wk plus 6 x 1000 mg every 12 wk in former TE patients) for an additional 20–21 months. Here we report only the pharmacokinetic aspects of the new TU formulation for the first approximately 2.5 yr of treatment. At baseline, serum T concentrations did not significantly differ between the two study groups. In the TE group, mean trough levels of serum T were always less than 10 nmol/liter before the next injection, whereas in the TU group, mean trough levels of serum T were 14.1 ± 4.5 nmol/liter after the first two doses (6-wk intervals) and 16.3 ± 5.7 nmol/liter after the 9-wk interval at wk 30. The mean serum levels of dihydrotestosterone and estradiol also increased in parallel to the serum T pattern and remained within the normal range. In the follow-up study, the former TU patients (n = 20) received eight TU injections at 12-wk intervals, and the TE patients (n = 16) switched to TU and initially received two TU injections at 8-wk intervals (loading) and continued with six TU injections at 12-wk intervals (maintenance). This regimen resulted in stable mean serum trough levels of T (ranging from 14.9 ± 5.2 to 16.5 ± 8.0 nmol/liter) and estradiol (ranging from 98.5 ± 45.2 to 80.4 ± 14.4 pmol/liter). The present study has shown that 1000 mg TU injected into male patients with hypogonadism at 12-wk intervals is well tolerated and leads to T levels within normal ranges, using four instead of 17 or more TE injections per year. An initial loading dose of either 3 x 1000 mg TU every 6 wk at the beginning of hormone substitution or 2 x 1000 mg TU every 8 wk after switching from the short-acting TE to TU were found to be a adequate dosing regimens for starting of treatment with the long-acting TU preparation.

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