A middle-aged man with BPH (Benign Prostatic Hyperplasia) symptoms and a smooth, symmetrically enlarged prostate experiences improved urinary symptoms and decreased prostate volume after starting a new medication, which medication is most likely responsible for the decreased prostate volume?

Finasteride is Most Likely Responsible for Decreased Prostate Volume

Finasteride is the medication most likely responsible for the decreased prostate volume in this patient, as it is the only agent among the options that reduces prostate size through inhibition of 5-alpha reductase, blocking conversion of testosterone to dihydrotestosterone. 1, 2

Mechanism and Evidence for Prostate Volume Reduction

• Finasteride reduces prostate volume by approximately 18-26% after 6-12 months of therapy, which aligns with the clinical scenario described 1, 3, 4
• The drug works by inhibiting 5-alpha reductase, reducing prostatic dihydrotestosterone levels and causing regression of hyperplastic prostatic tissue 1, 5
• The American Urological Association guidelines specifically state that 5-alpha reductase inhibitors (finasteride, dutasteride) are appropriate for patients with demonstrable prostatic enlargement and can reduce prostate size 1

Why Other Options Are Incorrect

• Tamsulosin (Option D) is an alpha-blocker that relaxes prostatic smooth muscle to improve urinary flow but does not reduce prostate volume 1, 6
• Tadalafil (Option C) is a phosphodiesterase-5 inhibitor that may improve LUTS through smooth muscle relaxation but does not decrease prostate size 6
• Tolterodine (Option E) is an antimuscarinic agent for overactive bladder that has no effect on prostate volume and may actually worsen obstructive symptoms in BPH 7
• Phenazopyridine (Option B) is a urinary analgesic with no mechanism to reduce prostate volume 8

Clinical Timeline Supports Finasteride

• Finasteride requires minimum 3-6 months for effectiveness, with maximum benefit at 12 months, matching the "months of therapy" timeframe described 6, 3
• Alpha-blockers like tamsulosin work within 2-4 weeks but provide no volume reduction 6, 9

Additional Supporting Evidence

• FDA labeling confirms finasteride reduces prostate volume and improves symptoms in men with enlarged prostates 2
• Studies demonstrate finasteride achieves approximately 19-20% reduction in prostatic volume compared to 3% with placebo 2, 4
• The combination of symptom improvement AND volume reduction is pathognomonic for 5-alpha reductase inhibitor therapy 1, 3

Critical Clinical Consideration

• The patient should be counseled that finasteride reduces PSA levels by approximately 50%, so any future PSA values should be doubled for cancer screening purposes 3, 5