PDE5 Inhibitors + Nitrates
Sildenafil/Tadalafil + Nitroglycerin = catastrophic synergism on cGMP pathway -> profound refractory hypotension and cardiovascular collapse. Strictly CONTRAINDICATED.
Tamoxifen vs. Raloxifene
Tamoxifen: ER antagonist in breast, agonist in bone AND ENDOMETRIUM (risk of endometrial cancer). Raloxifene: ER antagonist in breast AND ENDOMETRIUM, agonist in bone.
BPH Pharmacotherapy
Tamsulosin: selective alpha-1A blocker (rapid smooth muscle relaxation; floppy iris syndrome). Finasteride: 5-alpha reductase inhibitor (shrinks prostate over 6–12 months).
Bisphosphonates Protocol
Alendronate: pyrophosphate analog inhibiting osteoclast farnesyl pyrophosphate synthase. Take with full glass of water, upright for 30 min (prevents corrosive pill esophagitis).
SERMs, Hormonal Contraceptives & Androgen Antagonists
Selective Estrogen Receptor Modulators (SERMs) exert tissue-specific agonist and antagonist activities:
| Medication | Mechanism of Action | Breast Tissue | Endometrial Tissue | Bone & Lipids | Key High-Yield Indications & Risks |
|---|---|---|---|---|---|
| Tamoxifen | Selective Estrogen Receptor Modulator | Antagonist (blocks ER+ breast cancer growth) | Agonist (↑ risk of endometrial hyperplasia and cancer) | Agonist (maintains bone density, ↓ LDL) | Adjuvant therapy for ER/PR-positive breast cancer; hot flashes; increased risk of DVT and PE |
| Raloxifene | Selective Estrogen Receptor Modulator | Antagonist (reduces breast cancer risk) | Antagonist (NO increased endometrial cancer risk) | Agonist (↑ bone mineral density) | Prevention and treatment of postmenopausal osteoporosis; ↑ thromboembolic DVT/PE risk |
| Combined Oral Contraceptives | Estrogen (Ethinyl estradiol) + Progestin | Slight ↑ breast cancer risk | Protective against endometrial and ovarian cancer | Maintains bone density | Prevents pregnancy via LH surge suppression (blocks ovulation) and thickens cervical mucus; contraindicated in smokers > 35 (stroke/MI) |
| Clomiphene | Estrogen receptor antagonist in hypothalamus | Neutral | Neutral | Neutral | Blocks negative feedback of estrogen on GnRH → ↑ LH and FSH release → stimulates ovulation; first-line for PCOS infertility; multiple gestations |
Urologic Agents & Osteoporosis Therapeutics
Managing lower urinary tract symptoms, erectile dysfunction, and skeletal demineralization:
| Drug Class | Specific Drugs | Mechanism of Action | High-Yield Clinical Pearls & Toxicities |
|---|---|---|---|
| Alpha-1A Blockers | Tamsulosin, Alfuzosin | Selectively block alpha-1A adrenergic receptors in prostatic smooth muscle and bladder neck | Rapid symptom relief for BPH; minimal vascular hypotension; causes Intraoperative Floppy Iris Syndrome (IFIS) during cataract surgery |
| 5-Alpha Reductase Inhibitors | Finasteride, Dutasteride | Inhibit 5-alpha reductase → blocks conversion of testosterone to dihydrotestosterone (DHT) | Reduces prostate volume by 25% over 6–12 months; decreases PSA by 50%; treats androgenic alopecia; adverse effects: erectile dysfunction, gynecomastia |
| PDE-5 Inhibitors | Sildenafil, Tadalafil, Vardenafil | Inhibit phosphodiesterase-5 → ↑ cGMP → corpus cavernosum smooth muscle relaxation | Erectile dysfunction and pulmonary arterial hypertension; Severe life-threatening hypotension with Nitrates; blue-tinted vision (inhibits retinal PDE6) |
| Bisphosphonates | Alendronate, Risedronate, Zoledronic acid | Pyrophosphate analogs; bind hydroxyapatite, inhibit osteoclast farnesyl pyrophosphate synthase | First-line for osteoporosis; take upright with water (corrosive pill-induced chemical esophagitis); osteonecrosis of the jaw, atypical femoral fractures |
| RANKL Inhibitor | Denosumab | Monoclonal antibody binding RANKL → mimics osteoprotegerin, blocks osteoclast maturation | Alternative for osteoporosis when bisphosphonates contraindicated (CKD); rapid rebound bone loss if discontinued |
Board Traps & Common Distractors
- Co-administration of Phosphodiesterase-5 (PDE-5) inhibitors (Sildenafil) with Organic Nitrates (Nitroglycerin, Isosorbide mononitrate) is ABSOLUTELY CONTRAINDICATED; profound cyclic GMP accumulation induces refractory, fatal cardiovascular hypotension.
- Tamoxifen increases the incidence of endometrial hyperplasia and uterine sarcoma in postmenopausal women; any abnormal vaginal bleeding in a woman on Tamoxifen mandates urgent endometrial sampling.
- Combined oral contraceptives (COCs) are strictly contraindicated in women age >= 35 who smoke >= 15 cigarettes/day due to an unacceptably high risk of acute myocardial infarction, ischemic stroke, and venous thromboembolism.