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

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 × 250 mg T enanthate (TE) im every 3 wk (n = 20) or 3 × 1000 mg TU im every 6 wk (loading dose) followed by 1 × 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 × 1000 mg TU every 12 wk in former TU patients and 2 × 1000 mg TU every 8 wk plus 6 × 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 ...