Reproductive, Urologic & Endocrine Pharmacology

Selective Estrogen Receptor Modulators (SERMs) bind intracellular estrogen receptors (ERα/ERβ) and induce distinct conformational changes that recruit either nuclear coactivators (agonist effect) or corepressors (antagonist effect) depending on the target tissue. Tamoxifen acts as an estrogen ANTAGONIST in breast tissue (used for ER-positive breast cancer treatment and chemoprevention in pre- and postmenopausal women, as well as painful male gynecomastia) and an estrogen AGONIST in trabecular bone (preventing osteoporosis), liver (increasing prothrombotic clotting factor synthesis → deep vein thrombosis and pulmonary embolism), and uterine endometrium (stimulating endometrial hyperplasia, polyps, and a 2- to 3-fold increased risk of endometrial adenocarcinoma—any abnormal vaginal bleeding on tamoxifen requires prompt endometrial biopsy!). Note that tamoxifen is a prodrug bioactivated by hepatic CYP2D6 into active endoxifen, so potent CYP2D6 inhibitors like fluoxetine, paroxetine, and bupropion must be avoided (use venlafaxine for hot flashes). Conversely, raloxifene is an estrogen ANTAGONIST in both breast AND endometrial tissue (zero endometrial cancer risk!) and an estrogen AGONIST in bone (approved for postmenopausal osteoporosis and breast cancer risk reduction; still increases DVT/PE and hot flashes). Clomiphene blocks hypothalamic ERs to remove negative feedback, surging GnRH/FSH/LH for ovulation induction in PCOS (though the aromatase inhibitor letrozole is now first-line for PCOS ovulation induction).

Combined hormonal contraceptives (oral pills, transdermal patches, vaginal rings) pair synthetic ethinyl estradiol with a progestin (levonorgestrel, norethindrone, norgestimate, desogestrel, or the antimineralocorticoid/antiandrogenic spironolactone analog drospirenone—which can cause hyperkalemia). Ethinyl estradiol suppresses pituitary FSH secretion to prevent dominant ovarian follicle selection, while the progestin suppresses the mid-cycle LH surge to prevent ovulation, thickens cervical mucus against sperm penetration, and thins the endometrium. Combined contraceptives confer major non-contraceptive benefits: they reduce the risk of endometrial and epithelial ovarian cancer by ~50%, improve dysmenorrhea, endometriosis, adenomyosis, and heavy menstrual bleeding, and treat PCOS hyperandrogenism/acne (by increasing hepatic sex hormone-binding globulin [SHBG], which binds and lowers free serum testosterone). However, because ethinyl estradiol stimulates hepatic synthesis of angiotensinogen and coagulation factors (Factors II, VII, VIII, IX, X, fibrinogen) while decreasing antithrombin III and Protein S, estrogen-containing contraceptives are strictly contraindicated (WHO Category 4) in: (1) Smokers age ≥35 years (≥15 cigarettes/day); (2) Migraine with aura at ANY age (high ischemic stroke risk); (3) History of or active DVT/PE or known thrombophilia (Factor V Leiden, Prothrombin G20210A, antiphospholipid syndrome); (4) Uncontrolled hypertension (≥160/100 mmHg), ischemic heart disease, stroke, or complicated valvular disease; (5) Active breast cancer; (6) Decompensated cirrhosis or hepatocellular adenoma/carcinoma; and (7) <21 days postpartum.

Lower urinary tract symptoms (LUTS: hesitancy, weak stream, nocturia, incomplete emptying) from Benign Prostatic Hyperplasia (BPH) involve both a dynamic component (smooth muscle tone in the prostatic stroma, prostatic urethra, and bladder neck mediated by sympathetic α_1A-adrenergic receptors) and a static anatomical component (androgen-driven hyperplasia of transitional/periurethral zone glands). For immediate symptom relief within days, α₁-antagonists are first-line: non-selective α_1A/1B/1D blockers (terazosin, doxazosin, prazosin) relax both prostatic smooth muscle and systemic vascular α_1B arterioles (treating concurrent hypertension, but causing first-dose orthostatic hypotension and syncope), whereas uroselective α_1A-antagonists (tamsulosin, silodosin, alfuzosin) selectively relax the prostate and bladder neck without lowering blood pressure (signature side effects: retrograde/anejaculation and intraoperative Floppy Iris Syndrome during cataract surgery). For enlarged prostates (>30–40 g), 5α-reductase inhibitors (finasteride [type II inhibitor] and dutasteride [type I & II inhibitor]) block the conversion of testosterone to potent dihydrotestosterone (DHT), shrinking prostate volume by 20–25% over 6 to 12 months and reducing acute urinary retention (also used at 1 mg/day for androgenetic alopecia; side effects: decreased libido, erectile dysfunction, gynecomastia, and 50% reduction in serum PSA—always multiply measured PSA by 2 when screening a patient on finasteride for >6 months!). Daily tadalafil (PDE-5 inhibitor) treats both BPH and erectile dysfunction simultaneously.

Urinary incontinence pharmacotherapy depends on distinguishing urgency incontinence / overactive bladder (detrusor overactivity) from stress incontinence (urethral hypermobility or intrinsic sphincter deficiency) and overflow incontinence (detrusor underactivity or outlet obstruction). During normal urine storage, sympathetic hypogastric nerve fibers (T11–L2) release norepinephrine onto β₃-adrenergic receptors (G_s → cAMP relaxation of the detrusor dome) and α₁-receptors (G_q contraction of the internal urethral sphincter); during micturition, pelvic splanchnic parasympathetic fibers (S2–S4) release acetylcholine onto M₃ muscarinic receptors (G_q → IP₃/Ca²⁺ contraction of the detrusor). After behavioral bladder training and pelvic floor (Kegel) exercises, overactive bladder is treated with either M₃-selective antimuscarinics (oxybutynin, tolterodine, solifenacin, darifenacin, fesoterodine, or quaternary trospium) or selective β₃-adrenergic agonists (mirabegron, vibegron). Because antimuscarinics like oxybutynin cause xerostomia, constipation, blurred vision, acute urinary retention, and central anticholinergic delirium/dementia risk (Beers Criteria) in older adults, mirabegron or vibegron is the preferred first-line pharmacotherapy in elderly patients (note that mirabegron can raise blood pressure and is contraindicated in severe uncontrolled hypertension ≥180/110 mmHg). Refractory detrusor overactivity is treated with cystoscopic intradetrusor onabotulinumtoxinA (cleaves SNAP-25 to block ACh release) or sacral neuromodulation.

One of the most foundational physiological laws tested in reproductive pharmacology is the hypothalamic-pituitary GnRH pulsatility paradox. Anterior pituitary gonadotrophs require intermittent, pulsatile GnRH stimulation (every 60–120 minutes) to maintain cell-surface G_q-coupled GnRH receptor expression and stimulate FSH and LH synthesis (exploited by pulsatile gonadorelin infusion pumps to induce ovulation or spermatogenesis in hypothalamic amenorrhea or Kallmann syndrome). Conversely, continuous, non-pulsatile administration of long-acting GnRH receptor agonists (leuprolide, goserelin, histrelin, nafarelin) causes rapid homologous desensitization, internalization, and downregulation of pituitary GnRH receptors—producing a profound "medical castration" (hypogonadotropic hypogonadism with suppressed FSH, LH, estradiol, and testosterone) used to treat metastatic prostate cancer, uterine leiomyomas (fibroids), endometriosis, central precocious puberty, and ER-positive premenopausal breast cancer. However, during the first 7 to 14 days of initiating leuprolide, initial receptor stimulation triggers a transient surge in LH and testosterone (the "tumor flare" phenomenon), which in men with vertebral prostate cancer metastases can precipitate acute epidural spinal cord compression or urinary tract obstruction. To prevent this flare, patients starting leuprolide must be co-administered an androgen receptor antagonist (flutamide, bicalutamide, enzalutamide, apalutamide) for the first 2–4 weeks—OR instead be started on a direct GnRH receptor ANTAGONIST (degarelix [SC] or relugolix / elagolix [oral]), which competitively blocks pituitary GnRH receptors immediately with zero LH/testosterone surge.

Obstetric emergencies require rapid selection of uterotonics (for postpartum hemorrhage from uterine atony—the #1 cause of PPH) or tocolytics (to delay preterm labor at <34 weeks gestation for 48 hours to allow antenatal betamethasone fetal lung maturation and magnesium sulfate fetal neuroprotection at <32 weeks). Among uterotonics, high-dose IV/IM oxytocin (activates myometrial G_q-coupled oxytocin receptors; structural homology with ADH causes SIADH-like water intoxication and hyponatremia at high infusion rates) is universally first-line, whereas second-line agents have strict medical contraindications: Methylergonovine (an ergot alkaloid α₁/5-HT₂ agonist that causes sustained tetanic uterine contraction and intense systemic/coronary vasoconstriction) is strictly contraindicated in hypertension, preeclampsia, and coronary/peripheral vascular disease; Carboprost tromethamine (15-methyl-PGF_2α) contracts both uterine and bronchial smooth muscle and is strictly contraindicated in asthma; and Misoprostol (PGE₁) or Dinoprostone (PGE₂) can be used safely in both asthma and preeclampsia (causes self-limited fever/shivering and diarrhea). Among tocolytics: Indomethacin (NSAID inhibiting prostaglandin synthesis) is preferred at <32 weeks gestation (strictly avoided at ≥32 weeks due to premature closure of the fetal ductus arteriosus and oligohydramnios); Nifedipine (DHP L-type Ca²⁺ blocker) is preferred at 32–34 weeks (avoid co-administration with magnesium sulfate due to synergistic neuromuscular blockade and hypotension); and Terbutaline (β₂-agonist) causes maternal tachycardia, pulmonary edema, hyperglycemia, and hypokalemia.

Prostate adenocarcinoma growth is driven by the androgen receptor (AR) transcription axis, allowing sequential pharmacologic blockade across five anatomical and enzymatic steps: (1) Hypothalamic-Pituitary Suppression via continuous GnRH agonists (leuprolide, goserelin) or direct GnRH antagonists (degarelix, relugolix) to abolish testicular Leydig cell LH stimulation; (2) Adrenal & Intratumoral Androgen Synthesis Blockade via abiraterone (or high-dose ketoconazole)—abiraterone irreversibly inhibits CYP17A1 (17α-hydroxylase and 17,20-lyase) in the testes, adrenal cortex, and prostate tumor cells, blocking conversion of pregnenolone/progesterone into DHEA and androstenedione (because CYP17A1 inhibition also blocks cortisol synthesis and raises ACTH, patients develop mineralocorticoid excess [deoxycorticosterone/aldosterone] presenting with hypertension, hypokalemia, and fluid retention—mandating always co-administering low-dose prednisone with abiraterone!); (3) Androgen Receptor Competitive Antagonism via first-generation flutamide/bicalutamide (hepatotoxic) or potent second-generation AR inhibitors (enzalutamide, apalutamide, darolutamide—which also block AR nuclear translocation and DNA binding; enzalutamide crosses the BBB and causes seizures); (4) Peripheral Testosterone-to-DHT Conversion Blockade via 5α-reductase inhibitors (finasteride, dutasteride); and (5) PARP Inhibition (olaparib, rucaparib) in metastatic prostate cancer harboring somatic or germline BRCA1/2 homologous recombination defects.

In Polycystic Ovary Syndrome (PCOS)—characterized by hyperandrogenism (hirsutism, acne, androgenic alopecia), oligo/anovulation, and insulin resistance with elevated LH:FSH ratio—first-line management for patients not attempting conception is a combined oral contraceptive (COC), which suppresses LH-driven ovarian theca cell androgen synthesis, increases hepatic SHBG to bind free testosterone, and provides progestin protection against unopposed estrogen-driven endometrial hyperplasia/carcinoma. When hirsutism persists after 6 months of COC therapy, spironolactone is added as the antiandrogen of choice: beyond blocking renal aldosterone receptors, spironolactone competitively antagonizes dihydrotestosterone binding at follicular androgen receptors and weakly inhibits 17α-hydroxylase/5α-reductase (strictly requires concurrent contraception because spironolactone causes feminization/ambiguous genitalia of a male fetus). Topically, eflornithine inhibits ornithine decarboxylase to slow facial hair growth. For Emergency Contraception after unprotected intercourse, the single most effective method (>99% up to 5 days) is insertion of a copper intrauterine device (Cu-IUD), which induces a sterile inflammatory foreign-body reaction toxic to sperm and oocytes without affecting ovulation; oral options are ulipristal acetate (a selective progesterone receptor modulator effective up to 120 hours [5 days] that delays follicular rupture even after the LH surge has begun) and high-dose levonorgestrel (effective up to 72 hours [3 days], with reduced efficacy in BMI ≥30 kg/m²).

Beyond contraception, combined estrogen-progestin pills, patches, and vaginal rings confer high-yield non-contraceptive board benefits: they significantly reduce the risk of endometrial adenocarcinoma and epithelial ovarian carcinoma (by ~50% with long-term use via suppression of incessant ovulation and unopposed estrogen proliferation), reduce colorectal cancer risk, treat primary dysmenorrhea and endometriosis, reduce heavy menstrual bleeding/iron-deficiency anemia, and improve acne vulgaris and hirsutism in PCOS (because estrogen increases hepatic synthesis of Sex Hormone-Binding Globulin [SHBG], which binds and lowers circulating free testosterone; fourth-generation antiandrogenic progestin drospirenone is a structural analog of spironolactone that blocks androgen and mineralocorticoid receptors—monitor serum potassium for hyperkalemia!). However, estrogen-containing contraceptives must NEVER be prescribed in patients with WHO Category 4 absolute contraindications: age ≥35 AND smoking ≥15 cigarettes/day, migraine with aura (at ANY age!), history of or active VTE (DVT/PE), thrombophilia (Factor V Leiden, prothrombin G20210A, antiphospholipid syndrome), ischemic heart disease, or stroke, uncontrolled hypertension (≥160/100 mmHg), current breast cancer, decompensated cirrhosis or hepatic adenoma / hepatocellular carcinoma, or within 21 days postpartum. In patients with estrogen contraindications (except active breast cancer!), progestin-only methods (levonorgestrel IUD, subdermal etonogestrel implant, depot medroxyprogesterone acetate [DMPA—causes reversible bone mineral density loss and weight gain], or norethindrone/drospirenone pills) or the non-hormonal Copper IUD (induces a sterile cytotoxic endometrial inflammatory reaction that is spermicidal; increases menstrual bleeding/cramping) are safe.

Emergency Contraception (Postcoital) Efficacy Hierarchy (within 120 hours / 5 days of unprotected intercourse): (1) Copper IUD (or 52-mg Levonorgestrel IUD) is the #1 most effective emergency contraceptive (>99.9% effective), maintains efficacy across all BMI categories, and provides ongoing long-acting reversible contraception (contraindicated in active cervicitis/PID or distorted uterine cavity); (2) Oral Ulipristal acetate (30 mg), a Selective Progesterone Receptor Modulator (SPRM) that delays ovulation even after the LH surge has begun (effective up to 120 hours; requires a prescription); and (3) Over-the-counter oral Levonorgestrel (1.5 mg), which blocks the LH surge ONLY if taken before the LH surge starts (most effective within 72 hours, and exhibits reduced efficacy in patients with overweight/obesity [BMI ≥25–30 kg/m²]). For medical termination of intrauterine pregnancy (≤10–11 weeks gestation), competitive progesterone receptor antagonist mifepristone (RU-486) causes decidual necrosis and placental detachment, followed 24–48 hours later by the PGE₁ analog misoprostol to induce uterine expulsion.

Selective Estrogen Receptor Modulators (SERMs) exhibit tissue-specific estrogen agonist or antagonist activity based on differential recruitment of nuclear coactivators versus corepressors: (1) Tamoxifen is an ER antagonist in breast tissue (used for ER/PR-positive breast cancer treatment and prophylaxis in pre- and postmenopausal women; bioactivated by CYP2D6 to endoxifen) and an agonist in bone (preserves bone density), but acts as a partial AGONIST in the endometrium (increasing risk of endometrial hyperplasia, polyps, and endometrial carcinoma). (2) Raloxifene is an ER antagonist in BOTH breast AND endometrial tissue and an agonist in bone (approved for postmenopausal osteoporosis and invasive breast cancer risk reduction with ZERO endometrial cancer risk!). Both tamoxifen and raloxifene cause hot flashes and increase DVT/PE thromboembolism risk. (3) Clomiphene citrate blocks estrogen receptors in the hypothalamus, abolishing negative feedback to stimulate pulsatile GnRH and pituitary FSH/LH secretion for ovulation induction in anovulatory infertility (PCOS). However, in PCOS infertility, the oral non-steroidal aromatase inhibitor Letrozole is now the #1 first-line ovulation-inducing agent (superior live-birth rate over clomiphene because peripheral aromatase inhibition lowers estrogen negative feedback without depleting endometrial or cervical mucus estrogen receptors!). In postmenopausal ER-positive breast cancer, Aromatase Inhibitors (anastrozole, letrozole [reversible non-steroidal]; exemestane [irreversible steroidal]) block peripheral adipose conversion of adrenal androstenedione/testosterone into estrone/estradiol (causing severe osteoporosis/fractures and arthralgias, but NO endometrial cancer or DVT risk), while fulvestrant and elacestrant are Selective Estrogen Receptor Degraders (SERDs) that act as pure ER antagonists across all tissues.

Medical castration (Androgen Deprivation Therapy, ADT) for advanced or metastatic prostate adenocarcinoma targets four sequential steps along the hypothalamic-pituitary-gonadal-adrenal axis: (1) Continuous GnRH Receptor Agonists (leuprolide, goserelin, triptorelin) vs. Direct GnRH Receptor Antagonists (degarelix [SC], relugolix [oral]): While physiological pulsatile GnRH (every 60–90 minutes) stimulates gonadotroph LH and FSH secretion, continuous leuprolide downregulates and desensitizes pituitary GnRH receptors after an initial 1–2 week LH/testosterone flare (which must be blocked by co-administering flutamide or bicalutamide!). By contrast, degarelix and relugolix competitively block pituitary GnRH receptors immediately with ZERO initial testosterone surge. (2) Adrenal/Testicular Steroidogenesis Inhibition: Abiraterone irreversibly inhibits 17α-hydroxylase / 17,20-lyase (CYP17A1) in the testes, adrenal cortex, and prostate tumor tissue, blocking all androgen synthesis. Board pearl: Inhibiting 17α-hydroxylase reduces cortisol, triggering a compensatory ACTH surge that drives deoxycorticosterone and corticosterone accumulation (mineralocorticoid excess: hypertension, hypokalemia, and fluid retention)—therefore, abiraterone MUST always be co-administered with low-dose prednisone to suppress ACTH! (3) Androgen Receptor (AR) Antagonists include first-generation (flutamide, bicalutamide, nilutamide—flutamide causes severe hepatotoxicity) and second-generation antiandrogens (enzalutamide, apalutamide, darolutamide—which additionally block AR nuclear translocation and DNA binding; enzalutamide crosses the BBB to cause seizures). (4) 5α-Reductase Inhibitors (finasteride [selective Type II], dutasteride [Type I & II]) block conversion of testosterone to DHT, shrinking prostate volume by ~25% over 6–12 months in BPH and treating male androgenetic alopecia (note: finasteride lowers serum PSA by ~50%—multiply measured PSA by 2 when screening for prostate cancer—and is strictly teratogenic to a male fetus if handled by a pregnant woman, causing ambiguous genitalia / hypospadias).

For rapid symptom relief in BPH (within days), Alpha₁-Adrenergic Antagonists relax smooth muscle in the prostatic stroma, prostatic urethra, and bladder neck (internal urethral sphincter). They are stratified into Non-selective alpha_1A/1B/1D blockers (terazosin, doxazosin, prazosin), which block vascular smooth muscle alpha_1B receptors to lower systemic blood pressure (ideal in a man with both BPH and hypertension, though they cause first-dose orthostatic hypotension and syncope in normotensive elderly patients), and Uroselective alpha_1A/1D blockers (tamsulosin, silodosin, alfuzosin), which selectively relax the prostate and bladder neck without affecting alpha_1B vascular tone (the preferred first-line agents in normotensive men or older adults at risk for falls; cause retrograde/abnormal ejaculation and Intraoperative Floppy Iris Syndrome [IFIS]). ThePDE-5 inhibitor tadalafil (5 mg daily) is also FDA-approved for concurrent BPH and erectile dysfunction. Conversely, for Overactive Bladder / Urge Incontinence (detrusor hyperreflexia), first-line pharmacotherapy after pelvic floor (Kegel) exercises consists of either (1) Muscarinic M₃ Antagonists (oxybutynin, tolterodine, solifenacin, darifenacin, trospium)—note that in older adults, oxybutynin crosses the BBB to cause anticholinergic cognitive decline/delirium, making the selective beta₃-adrenergic agonist Mirabegron (or Vibegron) (which relaxes the detrusor muscle during bladder filling via G_s/cAMP without ANY anticholinergic side effects; monitor BP in severe uncontrolled hypertension) the preferred board choice in geriatric patients!

Uterotonics for Labor Induction & Postpartum Hemorrhage: (1) Oxytocin is a nonapeptide synthesized in the paraventricular nucleus and released from the posterior pituitary that binds myometrial G_q-coupled oxytocin receptors (increasing IP₃/Ca²⁺). It is the #1 first-line agent for both labor induction/augmentation and postpartum hemorrhage prevention/treatment. High-yield board toxicity: at high doses, oxytocin cross-reacts with renal V₂ (ADH) receptors, causing free-water retention and severe dilutional hyponatremia / water intoxication seizures, as well as uterine tachysystole (>5 contractions in 10 minutes causing uteroplacental insufficiency and fetal late decelerations—immediately stop oxytocin, place mother in left lateral decubitus, give IV fluids/oxygen, and administer terbutaline!). (2) Methylergonovine (ergot alkaloid alpha₁ and 5-HT₂ agonist) induces sustained tetanic uterine contraction for PPH; it causes intense systemic vasoconstriction and is strictly contraindicated in hypertension, preeclampsia, or coronary artery disease. (3) Carboprost tromethamine (Hemabate, 15-methyl-PGF_2α) stimulates myometrial contraction in refractory PPH; it causes severe GI diarrhea and bronchoconstriction—making it strictly contraindicated in asthma! (4) Misoprostol (PGE₁ analog) and Dinoprostone (PGE₂ insert) promote cervical ripening (collagenase activation) and myometrial contraction; misoprostol is safe in both asthmatic and hypertensive PPH patients (causes dose-related shivering and pyrexia/fever).

Tocolytics for Preterm Labor (Tailored by Gestational Age & Maternal Comorbidities): When preterm labor occurs between 24 and 34 weeks gestation (and chorioamnionitis, placental abruption, and non-reassuring fetal status have been ruled out), short-term 48-hour tocolysis uses one of three agents: (1) Indomethacin (COX inhibitor blocking PGF_2α/PGE₂ synthesis)—preferred at <32 weeks gestation, but strictly contraindicated at ≥32 weeks due to premature closure of the fetal ductus arteriosus and oligohydramnios; (2) Nifedipine (dihydropyridine L-type Ca²⁺ channel blocker)—preferred at 32 to 34 weeks gestation (contraindicated in maternal hypotension or preload-dependent cardiac lesions); and (3) Terbutaline (beta₂-adrenergic agonist that increases myometrial cAMP to inhibit myosin light-chain kinase)—used acutely to abort uterine tachysystole, though prolonged use (>48–72 hours) causes maternal tachycardia, pulmonary edema, hypokalemia, and maternal hyperglycemia (leading to fetal hyperinsulinemia and neonatal hypoglycemia). Finally, IV Magnesium Sulfate acts as a physiological Ca²⁺ antagonist used for fetal neuroprotection (<32 weeks—reduces cerebral palsy risk!) and eclamptic seizure prophylaxis/treatment (cleared 100% renally; monitor sequentially for loss of patellar deep tendon reflexes [>7 mEq/L] → respiratory depression [>10 mEq/L] → cardiac arrest [>15 mEq/L]; immediate antidote is IV Calcium Gluconate).

Penile erection is a parasympathetic neurovascular reflex (pelvic splanchnic nerves, S2–S4, "Point = Parasympathetic"; whereas emission is sympathetic T11–L2 and ejaculation is somatic pudendal S2–S4, "Shoot = Sympathetic"). Cavernous nerve terminals and endothelial cells release Nitric Oxide (NO), which activates soluble guanylate cyclase in corpus cavernosum smooth muscle to convert GTP into cGMP, lowering intracellular Ca²⁺ and relaxing helicine arterioles to engorge the corpora cavernosa. Phosphodiesterase-5 (PDE-5) Inhibitors (sildenafil, vardenafil, tadalafil, avanafil) competitively inhibit PDE-5 degradation of cGMP, prolonging NO-dependent cavernosal vasodilation (note: PDE-5 inhibitors require sexual/nerve NO stimulation to generate cGMP; in patients with complete bilateral cavernous nerve transection after non-nerve-sparing radical prostatectomy, intracavernosal or intraurethral alprostadil [prostaglandin E₁, PGE₁] directly increases cAMP independently of nitric oxide!). Signature PDE-5 inhibitor toxicities include headache, facial flushing, dyspepsia, nasal congestion, cyanopsia (blue-green color vision tinting with sildenafil due to cross-inhibition of retinal rod/cone PDE-6), non-arteritic anterior ischemic optic neuropathy (NAION), sudden sensorineural hearing loss, priapism (>4 hours—aspirate cavernosal blood and inject intracavernosal alpha₁-agonist phenylephrine), and lethal hypotension when co-administered with any organic nitrate or riociguat.