Pharmacokinetic Evaluation and Dosing of Subcutaneous Testosterone Pellets
Pastuszak AW, Mittakanti H, Liu JS, Gomez LP, Lipshultz LI, Khera M. J Androl. 2012 Mar 8. [Epub ahead of print]

Abstract

Introduction and Objective: Subcutaneous testosterone (T) pellets are a viable treatment modality for hypogonadism. Optimal dosing, frequency of reimplantation, and long-term safety of T pellets remain incompletely elucidated parameters. Methods: A retrospective review of 273 patients treated for hypogonadism using subcutaneous T pellets was performed. Serum total T (TT), free T (FT), and estradiol (E) levels were analyzed as a function of time from implantation, number of pellets implanted (6-9 or 10-12), BMI (<25 or ≥25), number of implantations (up to 4 rounds, 501 insertions) and pre-implantation T levels (<300 or ≥300ng/dL). T decay was determined using linear regression and TT levels at day 1 post-implantation and the time for TT levels to reach 300ng/dL extrapolated for all variables. Results: Mean(SD) subject age was 56±12.6 years. Baseline TT was 328±202 ng/dL, FT 9.49±27.8 pg/mL and E 25.1±17.3 pg/mL. Extrapolated TT and FT peaks were lower in men receiving 6-9 pellets than 10-12, though decay rates differed insignificantly. E levels rose significantly in men receiving 10-12, but not 6-9 pellets. Men with BMI ≥25 attained lower TT peaks with slower decay than men with BMI <25 receiving 10-12 pellets, though 300ng/dL TT levels were reached at ~100 days in both groups. No differences were seen in decay rates for men with multiple implant rounds, and no differences in T peaks or decay rates were seen in men with pre-implant T <300 or ≥300ng/dL. One patient developed erythrocytosis and no PSA recurrences were observed in men with prostate cancer treated with T pellets. Conclusions: Men with BMI <25 should receive fewer pellets and re-implantation for all men should occur 100-120 days after prior implantation. Men receiving 10-12 pellets have higher E levels, potentially reflecting increased aromatization of testosterone. Reimplantation and pre-implantation TT levels do not affect pellet decay kinetics.