ACE inhibitor Study Guide

📖 Core Concepts ACE inhibitors (‑pril drugs): Block angiotensin‑converting enzyme → ↓ Ang II, ↑ bradykinin → vasodilation & reduced sodium‑water retention. Renin–Angiotensin–Aldosterone System (RAAS): Renin → Ang I → ACE → Ang II → vasoconstriction + aldosterone release. Bradykinin effect: Normally degraded by ACE; inhibition raises its level → prostaglandin‑mediated vasodilation but also dry cough & possible angio‑edema. Clinical impact: Lowers blood pressure, improves heart‑failure outcomes, slows diabetic nephropathy, reduces post‑MI mortality. 📌 Must Remember Suffix: All agents end in “‑pril”. Key adverse effects: Dry cough (≈12 %). Angio‑edema (≈0.7 %). Hyper‑kalemia (↓ aldosterone). ↑ serum creatinine ≤30 % (stabilizes 2–4 wk). Absolute contraindications: Pregnancy, prior ACE‑i angio‑edema, bilateral renal artery stenosis, hypersensitivity. Dose‑equivalence (antihypertensive): Enalapril 10 mg ≈ Lisinopril 20 mg ≈ Ramipril 5 mg. Mortality benefit: 10 % reduction vs. placebo/ARB (meta‑analysis). Pregnancy category: D – teratogenic, boxed warning for 2nd/3rd trimester. 🔄 Key Processes RAAS activation Low BP/volume → juxtaglomerular cells release renin. Renin cleaves angiotensinogen → Ang I. ACE action (normal) $$\text{ACE}: \text{Ang I} \xrightarrow{-2\text{aa}} \text{Ang II}$$ Ang II → vasoconstriction, aldosterone ↑, ADH ↑. ACE‑inhibitor action Bind ACE active site → block Ang I → Ang II conversion. Result: ↓ systemic vascular resistance, ↓ aldosterone → natriuresis, ↓ extracellular fluid. ↑ bradykinin → prostaglandin‑mediated vasodilation + cough/angio‑edema. 🔍 Key Comparisons ACE‑i vs. ARB ACE‑i ↓ Ang II and ↑ bradykinin → cough/angio‑edema. ARB blocks AT₁ receptor only → no bradykinin rise, lower cough risk. Captopril vs. other ACE‑i Shorter half‑life, higher side‑effect rate, crosses BBB. Dual blockade (ACE‑i + ARB) Slight BP gain but ↑ risk of hyper‑K⁺, AKI, and no mortality benefit (ONTARGET). ⚠️ Common Misunderstandings “All coughs mean ACE‑i” – other drugs (β‑blockers, bronchodilators) can cause cough; confirm bradykinin link. “ACE‑i always safe in renal disease” – can precipitate AKI in bilateral renal artery stenosis or volume depletion. “Higher dose always better” – excess ACE‑i raises creatinine >30 % → stop or reduce. 🧠 Mental Models / Intuition “Brake‑and‑gas” analogy: Brake = ACE‑i (reduces Ang II → slows vasoconstriction). Gas = Aldosterone (promotes Na⁺/water retention). Removing the brake also lifts the gas pedal (↓ aldosterone), giving a double‑dip BP drop. Bradykinin “side‑track”: Think of ACE as a two‑way street; blocking it sends traffic (bradykinin) down a side road → helpful vasodilation but occasional “construction” (cough/angio‑edema). 🚩 Exceptions & Edge Cases Pregnancy: Any trimester → teratogenic; switch to labetalol or hydralazine. Renal artery stenosis: ACE‑i can cause acute kidney injury; monitor creatinine closely. African‑descent patients: Higher angio‑edema incidence; consider ARB if cough problematic. High‑flux dialysis membranes: May increase ACE‑i clearance → adjust dose. 📍 When to Use Which First‑line hypertension: ACE‑i (especially with diabetes or proteinuria). Heart failure with reduced EF: ACE‑i → titrate to max tolerated dose. Post‑MI: Early ACE‑i (e.g., ramipril) for mortality reduction. Diabetic nephropathy: ACE‑i preferred over ARB for albuminuria control. Contraindicated: Pregnant patients, prior ACE‑i angio‑edema, bilateral renal artery stenosis → use ARB or alternative antihypertensives. 👀 Patterns to Recognize Cough + new ACE‑i → suspect bradykinin accumulation. ↑ creatinine ≤30 % + stable → expected; >30 % → stop or evaluate volume status. Hyper‑K⁺ + ACE‑i + K‑sparing diuretic → high‑risk scenario → check K⁺ within 1‑2 weeks. Angio‑edema after ACE‑i initiation → emergent airway protection; discontinue drug. 🗂️ Exam Traps Distractor: “ACE‑i increase aldosterone” – wrong; they decrease aldosterone. Misleading choice: “ACE‑i are contraindicated in all renal disease” – only in severe hypoperfusion or bilateral stenosis; mild CKD is often treated. Near‑miss: “Dual ACE‑i + ARB therapy improves survival” – ONTARGET shows no mortality benefit, only more adverse events. Confusion: “All ACE‑i have the same half‑life” – captopril is an exception (shorter). Answer trap: “Pregnancy is a relative contraindication” – actually an absolute contraindication (Category D).