Benign prostatic hyperplasia develops in the transition zone of the prostate and 5α-reductase inhibitors (5-ARIs) reduce prostate volume. We investigated whether oral treatment with the 5-ARIs dutasteride and finasteride more significantly affected volume reduction in the transition zone or in the entire prostate.

Total prostate and transition zone volumes (TPV and TZV) were measured at baseline using a transrectal ultrasound (TRUS), and then at 1 yr after the commencement of dutasteride (0.5 mg) or finasteride (5.0 mg). The ratio of TPV to TZV was used to determine the transition zone index (TZI). Volume reduction (%) was calculated as the ratio of volume reduction to baseline prostate volume. Additionally, serum prostate-specific antigen (PSA) concentrations were measured at baseline and then at 1 yr after the 5-ARIs were commenced.

All of the 43 patients (mean age, 68.5 yr ± 7.2; range, 53–82 yr) with clinical lower urinary tract symptoms suggestive of benign prostatic hyperplasia and who were 5-ARI-naïve were prescribed dutasteride (0.5 mg, 74.4%, 32/43) or finasteride (5.0 mg, 25.6%, 11/43) for more than 1 yr (13.5 ± 4.2 months). At baseline, the mean TPV, TZV, and TZI values were 58.0 ± 25.6 cm3, 30.8 ± 16.6 cm3, and 0.52 ± 0.13, respectively. At 1 yr after the commencement of the 5-ARIs, the mean TPV, TZV, and TZI values were 48.0 ± 23.5 cm3, 28.1 ± 19.0 cm3, and 0.55 ± 0.13, respectively. The TZI value is not significantly different at 1 yr compared with baseline (p > 0.05), while the TPV and TZV reductions are 22.7 ± 15.2% and 27.2 ± 16.8%, respectively; there is no significant difference between the TPV and TZV volume reductions (p > 0.05).

These results show that prostate volume reduction induced by 5-ARIs occurs in the entire prostate universally, rather than in the transition zone specifically.

Oral treatment with the 5-ARIs dutasteride and finasteride affected volume reduction in the entire prostate without more significant reduction in the transition zone.