Steady-State Pharmacokinetics of Oral Testosterone Undecanoate with Concomitant Inhibition of 5α-Reductase by Finasteride

This study investigated the effects of finasteride, a 5α-reductase inhibitor, on the pharmacokinetics of oral testosterone undecanoate (TU). The study found that finasteride was unable to suppress serum dihydrotestosterone (DHT) and increase serum testosterone after the oral administration of TU as compared with other tested formulations of oral testosterone. This may be due to the variable methods of absorption between these two oral formulations. The study also found that oral dosing of TU is associated with supraphysiological elevations in serum DHT, which may increase the risk of DHT-related conditions such as acne, benign prostatic hypertrophy, and androgenic alopecia.