Evaluation of drug-induced prostatic involution in dogs by transabdominal B-mode ultrasonography.

The relative antiandrogen-induced prostate involution activity of the newly synthesized hydroxyflutamide pro-drug was compared with that of flutamide in 25 Beagles. Secondary antiandrogen activity of both drugs on the testes and mammary tissue was investigated. Daily oral administration of both compounds at 2 dosages (ie, 2.5 and 5.0 mg/kg of body weight) during a 7-week period was monitored by transabdominal ultrasonography of the prostate twice a week. Cross-sectional area estimates of the prostate gland calculated from oblique dorsoventral, and transverse sonographic measurements were diminished significantly in some of the treated dogs as early as day 14 of drug administration. All treated dogs had significant differences in reduction by day 47. Involution was related directly to dose (P less than 0.05), but no difference was observed between test compounds. Differences in secondary antiandrogen activity were not remarkable. Flutamide was not found to have any activity advantage in vivo over hydroxyflutamide. It was concluded that ultrasonography can be a highly effective means of monitoring prostate size, and of monitoring drug-induced involution over time.