Oral testosterone in oil: pharmacokinetic effects of 5alpha reduction by finasteride or dutasteride and food intake in men.

Oral administration of 400 mg of testosterone (T) in oil, when combined with the 5alpha reductase inhibitor dutasteride (D), elevates serum T in medically castrated men to the normal range. In this study, we sought to determine the impact of 1) finasteride (F) and 2) food intake on the serum T and dihydrotestosterone (DHT) levels observed after the oral administration of T in oil. Therefore, we conducted a pharmacokinetic study of oral T in oil, alone or with D or F, in the fasting and fed states in normal men whose endogenous T production was suppressed by the GnRH antagonist acyline. After acyline administration, 7 healthy men (mean age 31 +/- 8 years) were sequentially administered five 400-mg doses of oral T in sesame oil once daily. The first dose of oral T (T-alone) in oil was given while fasting without F or D. The second (fasting) and third (fed) doses were administered after pretreatment with F (T + F). Four days later, the fourth (fasting) and fifth (fed) doses were administered after pretreatment with D (T + D). Blood samples for measurement of serum T and DHT were obtained before T dosing and 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours after each administration. In the fasting state, 24-hour area-under-the-curve of serum T after oral T administration was significantly greater with coadministration of either D or F compared with T-alone (126 +/- 36 nmol-h/L [T-alone] vs 287 +/- 98 nmol-h/L [T + F] vs 236 +/- 82 nmol-h/L [T + D]; P < .05 for T + F and T + D vs T-alone). Administration of the T with food nonsignificantly decreased serum T levels compared with fasting administration. The administration of oral T in oil combined with either F or D results in serum T levels adequate to treat men with testicular failure. Additional studies of the combination of oral T in oil with 5alpha-reductase inhibitors as a novel form of oral T therapy are warranted.