Testosterone implants in women: pharmacological dosing for a physiologic effect.

Objectives: The objectives of this study were to determine therapeutic serum testosterone (T) levels/ranges and inter-individual variance in women treated with subcutaneous T implants.

Study Design: In study group 1, T levels were measured at two separate time intervals in pre- and post-menopausal women treated with subcutaneous T for symptoms of androgen deficiency: (i) four weeks after pellet insertion, and (ii) when symptoms of androgen deficiency returned. In a separate pharmacokinetic study (study group 2), 12 previously untreated postmenopausal women each received a 100mg T implant. Serum T levels were measured at baseline, 4 weeks and 16 weeks following T pellet implantation. In study 'group' 3, serial T levels were measured throughout a 26 h period in a treated patient.

Results: In study group 1, serum T levels measured at 'week 4' (299.36±107.34 ng/dl, n=154), and when symptoms returned (171.43±73.01 ng/dl, n=261), were several-fold higher compared to levels of endogenous T. There was significant inter-individual variance in T levels at 'week 4' (CV 35.9%) and when symptoms returned (CV 42.6%). Even with identical dosing (study group 2), there was significant inter-individual variance in T levels at 'week 4' (CV 41.9%) and 'week 16' (CV 41.6%). In addition, there was significant intra-individual circadian variation (CV 25%).

Conclusions: Pharmacologic dosing of subcutaneous T, as evidenced by serum levels on therapy, is needed to produce a physiologic effect in female patients. Safety, tolerability and clinical response should guide therapy rather than a single T measurement, which is extremely variable and inherently unreliable.