ACE Inhibitors

ACE inhibitors don't just lower blood pressure — they protect kidneys and remodel damaged hearts. Understanding the mechanism explains why they're first-line for so many conditions.

ACE inhibitors (lisinopril, enalapril, captopril, ramipril — the "-pril" drugs) block angiotensin-converting enzyme, which normally converts angiotensin I to angiotensin II. Angiotensin II is a potent vasoconstrictor that also triggers aldosterone release, causing sodium and water retention. By blocking this conversion, ACE inhibitors produce vasodilation, reduce preload and afterload, and decrease aldosterone-driven fluid retention. This mechanism makes them first-line therapy for hypertension, heart failure with reduced ejection fraction (HFrEF), and diabetic nephropathy. In heart failure, they reduce cardiac workload and slow ventricular remodeling — the progressive chamber dilation that worsens outcomes. In diabetic kidney disease, they dilate the efferent arteriole of the glomerulus, reducing intraglomerular pressure and slowing proteinuria progression. ACE inhibitors also raise bradykinin levels (because ACE normally degrades bradykinin), which contributes to vasodilation but also explains the characteristic dry cough — a side effect covered in the sibling atom, not here.

Key Distinctions

Don't confuse the mechanism of ACE inhibitors (block conversion of angiotensin I → II) with ARBs (block angiotensin II at the receptor). Both reduce angiotensin II activity, but ACE inhibitors also raise bradykinin — ARBs do not. Students often think ACE inhibitors are prescribed only for blood pressure; the renal-protective and cardiac-remodeling indications are equally high-yield and frequently tested.

Clinical Pearl

Think "ACE = Afterload Cut, Efferent arteriole dilated." That's why they help both the failing heart and the diabetic kidney — two birds, one mechanism.

Adverse Effects & Nursing

ACE inhibitors (lisinopril, enalapril, ramipril) block the breakdown of bradykinin, which accumulates in lung tissue and triggers a dry, nonproductive cough in up to 20% of patients. This cough is not dose-dependent and won't resolve with cough suppressants — the drug must be switched, typically to an ARB. The life-threatening adverse effect is angioedema: swelling of the lips, tongue, and throat that can obstruct the airway. It can occur at any point during therapy, even years after initiation, and requires immediate drug discontinuation and emergency airway management. Hyperkalemia is the key lab concern because reduced aldosterone secretion causes potassium retention. Monitor serum potassium closely, especially if the patient also takes potassium-sparing diuretics or potassium supplements. Baseline and periodic monitoring of BUN, creatinine, and potassium is required. First-dose hypotension is common — have the patient sit or lie down after the initial dose and monitor blood pressure for 2 hours. ACE inhibitors are absolutely contraindicated in pregnancy (teratogenic, especially second and third trimesters) — teach all patients of childbearing potential to use reliable contraception and report suspected pregnancy immediately.

Key Distinctions

Don't confuse the ACE inhibitor cough (dry, persistent, bradykinin-mediated) with a respiratory infection or worsening heart failure (productive cough, crackles, dyspnea). Angioedema from ACE inhibitors can appear months to years into therapy — students assume it only happens with the first dose. Hyperkalemia, not hypokalemia, is the electrolyte risk; this is the opposite of loop diuretics, which are often co-prescribed.

Clinical Pearl

Cough is annoying, angioedema is deadly — both come from the same bradykinin buildup. If the lips start swelling, stop the drug and protect the airway first.