Effect of finasteride (Proscar MSD) on seminal composition, prostate function and fertility in male dogs

This study reports the long-term effects and reversibility of the administration of Finasteride, a 5 alpha-reductase inhibitor, on the prostate, prostatic fluid composition and volume, sperm output and characteristic, and fertility of adult beagle dogs treated for 21 weeks at a dose of 1 mg kg-1 body weight. Finasteride was not associated with any side effects. After 5 to 15 weeks of treatment, it induced a marked decrease in the size of the prostate and a fall in its secretions and in the production of spermatozoa. Sperm concentration increased and was inversely correlated with the decrease in the volume of prostatic secretions. At maximum effect, the calculated prostate volume was reduced to 30% of the initial value, and together with the reduced prostatic secretion, no ejaculate could be collected despite normal behaviour. These effects were reversible in 6 to 8 weeks after the cessation of treatment. Matings at 20 to 22 weeks after the start of treatment were fertile, demonstrating the absence of long-term effects of this treatment on male fertility. As fertility was not impaired and prostatic benign hyperplasia successfully regressed. Finasteride treatment in this preliminary study appears to be an interesting alternative therapy in valuable breeding dogs with benign prostatic hyperplasia.