Pharmacokinetic Profile of Subcutaneous Testosterone Enanthate Delivered via a Novel, Prefilled Single‐Use Autoinjector: A Phase II Study

INTRODUCTION Hypogonadism is one of the most common male endocrine problems. Although many treatments are currently available, unmet need exists for new testosterone (T) replacement therapies that are simple to administer and use, are safe, and mimic physiologic T levels. AIM The study aim was to determine the pharmacokinetics (PK), safety, and tolerability of T enanthate (TE) administered via a novel single-use autoinjector system, which was designed to eject high-viscosity solutions from a prefilled syringe fitted with a five-eighths-inch 27-gauge needle. METHODS Thirty-nine men with hypogonadism entered this dose-finding, open-label, parallel-group study. Patients were washed out of their topical T regimens and randomized to receive 50 or 100 mg of subcutaneous (SC) TE weekly. The reference group were patients with hypogonadism who were maintained on standard 200-mg intramuscular (IM) TE. MAIN OUTCOME MEASURE The primary outcome measure was the PK profile of SC TE, analyzed in reference to T levels used by the Food and Drug Administration to approve T products. Secondary outcome measures were safety and tolerability assessments. RESULTS Both doses of SC TE achieved normal average concentrations of serum T within a 168-h dosing interval after injection. Concentration ranges were similar at all time points following 50-mg SC TE injections and following the third injection in the 100-mg arm. Mean steady-state T concentration at week 6 was 422.4 and 895.5 ng/dL for the 50- and 100-mg SC TE arms, respectively. SC TE demonstrated PK dose proportionality. SC TE restored normal serum T with low variation relative to 200-mg IM without clinically significant adverse events. CONCLUSIONS Administration of TE via this novel injection system restored T levels to normal range in men with hypogonadism. SC TE dosed weekly demonstrated steady, dose-proportional measures of exposure and was well-tolerated. Kaminetsky J, Jaffe JS, Swerdloff RS. Pharmacokinetic profile of subcutaneous testosterone enanthate delivered via a novel, prefilled single-use autoinjector: A phase II study. Sex Med 2015;3:263-273.