7.4 Urologic Disorders: BPH, Overactive Bladder, and Erectile Dysfunction

Why Urology Matters on the BCPS Exam

Urologic disorders sit within Domain 1C, Tertiary Pharmacotherapy Specialty Areas (1C7 Urology) of the September 2024 Pharmacotherapy Content Outline. Although 1C carries a lower weight (9%) than the primary and secondary specialty areas, the BCPS reliably tests the three highest-volume ambulatory conditions a pharmacotherapy specialist manages: benign prostatic hyperplasia (BPH), overactive bladder (OAB), and erectile dysfunction (ED). The questions are rarely trivia; they probe drug selection, onset of effect, adverse-event trade-offs, and dangerous drug interactions that overlap with cardiology, geriatrics, and psychiatry.

Benign Prostatic Hyperplasia (BPH)

BPH produces lower urinary tract symptoms (LUTS) from static (prostatic enlargement) and dynamic (smooth-muscle tone) obstruction. Guideline-directed therapy (AUA) matches the mechanism to the pathology.

Alpha-1 Adrenergic Antagonists

Alpha-1 blockers relax prostatic and bladder-neck smooth muscle, relieving the dynamic component. They improve symptoms within days and are first-line for bothersome LUTS.

• Uroselective (alpha-1A) agents — tamsulosin, silodosin: less effect on vascular alpha-1B receptors, so less orthostatic hypotension but more ejaculatory dysfunction and a risk of intraoperative floppy iris syndrome (IFIS) during cataract surgery. Screen for planned cataract surgery before starting.
• Non-selective agents — alfuzosin, doxazosin, terazosin: more blood-pressure lowering (useful if concomitant hypertension, but a fall/syncope risk in the elderly). Doxazosin and terazosin require dose titration at bedtime to limit first-dose orthostasis.

Alpha blockers do not shrink the prostate and do not lower PSA.

5-Alpha-Reductase Inhibitors (5-ARIs)

Finasteride and dutasteride block conversion of testosterone to dihydrotestosterone (DHT), shrinking the static glandular component. Key testable facts:

• Onset is slow — 3 to 6 months for maximal benefit; best for men with enlarged prostates (>40 mL) or elevated PSA.
• They reduce serum PSA by approximately 50%. To screen for prostate cancer in a man on a 5-ARI, double the measured PSA value.
• Adverse effects: decreased libido, erectile dysfunction, ejaculatory dysfunction, gynecomastia. They are teratogenic — pregnant or potentially pregnant individuals must not handle crushed or broken tablets.

Combination and Adjunct Therapy

• Alpha blocker + 5-ARI (e.g., dutasteride/tamsulosin) is superior to monotherapy for men with large prostates at risk of progression (CombAT-type data).
• Tadalafil 5 mg daily (a PDE5 inhibitor) is FDA-approved for BPH-LUTS and is useful when BPH and ED coexist.
• Antimuscarinics or mirabegron may be added for predominant storage/OAB symptoms once significant obstruction is excluded.

Overactive Bladder (OAB)

OAB is urinary urgency, usually with frequency and nocturia, with or without urgency incontinence. After behavioral therapy (bladder training, fluid management, pelvic-floor exercises), pharmacotherapy targets detrusor overactivity.

Antimuscarinics (Anticholinergics)

Oxybutynin, tolterodine, solifenacin, fesoterodine, trospium, darifenacin block muscarinic (M3) receptors to reduce detrusor contraction.

• Class effects: dry mouth, constipation, blurred vision, urinary retention, and cognitive impairment. Immediate-release oxybutynin has the highest anticholinergic burden.
• Beers Criteria flags oral antimuscarinics as potentially inappropriate in older adults because of CNS effects and cumulative anticholinergic burden, which is associated with dementia risk.
• Trospium is a quaternary amine that poorly crosses the blood-brain barrier — a reasonable choice when CNS effects are a concern.
• Avoid in narrow-angle glaucoma and in men with untreated bladder outlet obstruction (precipitates acute urinary retention).

Beta-3 Adrenergic Agonists

Mirabegron and vibegron relax the detrusor during storage without anticholinergic effects, making them preferred in older adults and in patients already carrying a high anticholinergic load. Mirabegron can raise blood pressure and is a moderate CYP2D6 inhibitor (watch metoprolol, some antidepressants); vibegron has a cleaner interaction profile and does not require blood-pressure-based restrictions to the same degree.

Refractory OAB

OnabotulinumtoxinA bladder injection, percutaneous tibial nerve stimulation, and sacral neuromodulation are third-line options after oral therapy fails.

Erectile Dysfunction (ED)

Phosphodiesterase-5 (PDE5) inhibitors — sildenafil, tadalafil, vardenafil, avanafil — are first-line. They enhance nitric-oxide-mediated cGMP to promote cavernosal smooth-muscle relaxation.

• Absolute contraindication with nitrates (nitroglycerin, isosorbide) and with the guanylate cyclase stimulator riociguat — the combination causes life-threatening hypotension. After sildenafil/vardenafil, wait 24 hours before a nitrate; after tadalafil, wait 48 hours.
• Additive hypotension with alpha-blockers — separate dosing and start low; tadalafil 5 mg daily is best tolerated with alpha-blockers.
• Tadalafil has the longest half-life (~17.5 hours), enabling once-daily dosing and dual use for BPH-LUTS and pulmonary arterial hypertension.
• Adverse effects: headache, flushing, dyspepsia, nasal congestion, dose-dependent visual changes (sildenafil), and rare NAION. Counsel on priapism (>4 hours = emergency).

ED is also frequently drug-induced — thiazides, non-selective beta-blockers, SSRIs, spironolactone, and finasteride are common culprits; reviewing the medication list is a core pharmacotherapy intervention before adding a PDE5 inhibitor.