Population Pharmacokinetic Modeling and Simulations to Evaluate a Potential Dose Regimen of Testosterone Undecanoate...

Intramuscular testosterone undecanoate is indicated as testosterone replacement in adult males with a deficiency in or absence of endogenous testosterone (hypogonadism). Intramuscular testosterone undecanoate 750 mg is approved to be administered at initiation and at 4 weeks, followed by a maintenance dose every 10 weeks. However, a more frequent maintenance regimen may improve symptom management of low testosterone at the end of each dosing interval. The current objective was to develop a population pharmacokinetic (PK) model for intramuscular testosterone undecanoate 750 mg and to perform PK simulations to assess the impact of an 8-week maintenance regimen on testosterone exposure. A 1-compartment model with first-order absorption and first-order elimination best described the PK of testosterone undecanoate. The model included time-dependent suppression and gradual recovery of endogenous testosterone production during testosterone undecanoate administration. Significant covariates included body weight and sex hormone-binding globulin level. With the final PK model, simulations were performed to evaluate the impact of an 8-week vs a 10-week maintenance regimen on testosterone exposure. The 8-week testosterone undecanoate regimen had a predicted 11% increase in average concentration and last observed concentration during a dosing interval before a subsequent dose and a 5% increase in maximum concentration. This translated into an ≈10% increase in the percentage of patients predicted to have a last observed concentration during a dosing interval before a subsequent dose >300 ng/dL, minimal change in the percentage of patients with average concentration in the normal range, and a low likelihood of maximum concentration >2500 ng/dL. These simulations suggest that more frequent administration of intramuscular testosterone undecanoate may be beneficial in some patients. Further clinical evaluation of an 8-week dose regimen is warranted.