## Benign Prostatic Hyperplasia: Pharmacological Management **Key Point:** Finasteride is the only 5-alpha reductase inhibitor that directly reduces prostate volume by inhibiting the conversion of testosterone to dihydrotestosterone (DHT), the primary driver of benign prostatic hyperplasia. ### Mechanism of Action Finasteride blocks 5-alpha reductase, preventing DHT synthesis in the prostate. This leads to: - Actual reduction in prostate size (15–30% volume reduction over 6–12 months) - Improvement in urinary flow rate - Decreased risk of acute urinary retention and need for surgery ### Drug Comparison in BPH | Drug Class | Drug Name | Mechanism | Effect on Prostate Volume | Onset of Action | |---|---|---|---|---| | 5-α Reductase Inhibitor | Finasteride | Blocks DHT synthesis | **Reduces** | 6–12 months | | Alpha-1 Blocker | Tamsulosin, Doxazosin | Relaxes smooth muscle | No change | 1–2 weeks | | PDE-5 Inhibitor | Tadalafil | Smooth muscle relaxation | No change | 2–4 weeks | **High-Yield:** Finasteride is the **only agent that reduces prostate volume**. All other drugs merely relieve obstruction symptoms without shrinking the gland. ### Clinical Pearl Finasteride is particularly effective in men with: - Prostate volume > 40 mL - Elevated PSA levels - Risk factors for progression (age > 50, moderate-to-severe symptoms) ### Timing Expectation - Alpha-blockers (tamsulosin, doxazosin) provide **rapid symptom relief** (1–2 weeks) but do NOT reduce prostate size - Finasteride requires **6–12 months** for maximal effect but provides durable volume reduction - **Combination therapy** (5-α reductase inhibitor + alpha-blocker) is superior to monotherapy in moderate-to-severe BPH with large prostate **Warning:** Do not confuse symptom relief with disease modification. Tamsulosin and doxazosin relieve symptoms but do not prevent progression; finasteride does both. [cite:Robbins 10e Ch 20]
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