Pharmacokinetic Profile of Subcutaneous Testosterone Enanthate Delivered via a Novel, Prefilled Single-Use Autoinjector: A Phase II Study.
Level 2 - randomized trial
Randomized, open-label, parallel-group dose-finding trial
PubMed 26797061 · doi:10.1002/sm2.80
What was done
Thirty-nine men with hypogonadism underwent washout from prior topical testosterone therapies and were randomized in an open-label, parallel-group phase II trial to receive weekly subcutaneous testosterone enanthate via a prefilled single-use autoinjector (27-gauge, 5/8-inch needle) at either 50 mg or 100 mg. A reference cohort was maintained on standard 200-mg intramuscular testosterone enanthate. The primary outcome was the pharmacokinetic profile across a 168-hour dosing interval over 6 weeks evaluated against FDA benchmarks, alongside safety and tolerability.
What was found
Both subcutaneous doses restored average serum testosterone to the normal range across the 168-hour interval. Mean steady-state testosterone concentrations at week 6 were 422.4 ng/dL for the 50-mg group and 895.5 ng/dL for the 100-mg group, demonstrating dose proportionality. Subcutaneous delivery produced low concentration variation relative to the 200-mg intramuscular regimen without clinically significant adverse events.
Why it matters
This autoinjector system offers an effective subcutaneous alternative to standard intramuscular testosterone therapy, achieving stable, dose-proportional physiological levels without requiring high-volume deep intramuscular injections.
Limits
The study is limited by a small sample size (n = 39 across three arms), an open-label design, and a short 6-week observation period. The abstract does not provide exact numerical pharmacokinetic dispersion metrics, specific adverse event counts, or patient-reported ease-of-use scores.
Cited by
- supports Subcutaneous injection of testosterone provides slower absorption and more stable serum hormone concentrations compared to intramuscular injection.