A 72-year-old man has had increasing difficulty with urination for the past 10 years. He now has to get up several times each night because of a feeling of urgency, but each time the urine volume is not great. He has difficulty starting and stopping urination. On physical examination, the prostate is enlarged to twice its normal size but is not tender to palpation. One year ago, his serum prostate-specific antigen (PSA) level was 6 ng/mL, and it is still at that level when retested. Which of the following drugs is most likely to be effective in the treatment of this man?

The clinical features are typical of nodular prostatic hyperplasia causing a slight elevation of the PSA level. A PSA level that remains unchanged for 1 year, as in this case, is less likely to be found with prostate cancer. Finasteride is a 5a-reductase inhibitor that decreases the formation of dihydrotestosterone (DHT) that binds to androgen receptors in prostatic stromal and epithelial cells, driving proliferation with prostate gland enlargement. However, a1-adrenergic blockers that diminish smooth muscle tone are somewhat more effective in treating nodular hyperplasia. Estrogen therapy has been used as antihormonal therapy in prostate cancer. Mitoxantrone is a chemotherapy agent that, when given with prednisone, has been shown to be effective in treating advanced prostate cancers. Nitrofurantoin is an antibiotic that is often used in treating urinary tract infections.