Antihypertensive Drugs: Classes, Sites of Action & Choice

Blood pressure is simply cardiac output × systemic vascular resistance. Every antihypertensive drug lowers one or both — and the cleanest way to learn the classes is by the organ they act on. The map below ties the whole topic together.

1. Diuretics

Thiazides (hydrochlorothiazide, chlorthalidone) are first-line in many patients — they lower volume initially and reduce peripheral resistance long-term. Watch for hypokalaemia and the “hyperGLUC” metabolic effects.

2. ACE inhibitors & ARBs (the RAAS blockers)

• ACE inhibitors (“-prils”) block conversion of angiotensin I → II: vasodilation + less aldosterone. Signature side effect: dry cough (bradykinin); also hyperkalaemia, angioedema. Contraindicated in pregnancy and bilateral renal artery stenosis.
• ARBs (“-sartans”) block the AT1 receptor — same benefits, no cough. First choice when ACE inhibitors aren’t tolerated.
• Both are renoprotective — preferred in diabetes and proteinuria.

3. Calcium channel blockers

• Dihydropyridines (amlodipine, nifedipine) act mainly on vessels — vasodilation; side effect: ankle oedema, flushing.
• Non-dihydropyridines (verapamil, diltiazem) act more on the heart — useful in arrhythmia; avoid combining with β-blockers (bradycardia/block).

4. β-blockers

Reduce cardiac output and renin (“-olols”). No longer first-line for uncomplicated hypertension but valuable with ischaemic heart disease, heart failure, or arrhythmia. Avoid abrupt withdrawal (rebound) and use caution in asthma.

5. Other agents

• α1-blockers (prazosin, doxazosin) — also help benign prostatic hyperplasia; first-dose hypotension.
• Central α2-agonists (clonidine, methyldopa) — methyldopa is the drug of choice in pregnancy.
• Direct vasodilators (hydralazine, minoxidil) and, in emergencies, sodium nitroprusside.

Choosing the right drug

• Young (<55), non-Black: start ACE inhibitor / ARB.
• Older or Black patients: CCB or thiazide.
• Diabetes / proteinuria: ACE inhibitor or ARB.
• Pregnancy: methyldopa, labetalol, nifedipine.
• Hypertensive emergency: IV labetalol, nitroprusside, or nicardipine.

Exam tip: anchor each class to its site on the diagram, then attach the one signature point examiners want — ACE inhibitor → cough, dihydropyridine CCB → ankle oedema, methyldopa → pregnancy, verapamil → don’t combine with a β-blocker.

Hypertension is the most common condition you’ll prescribe for. Master these five groups by site of action and “compelling indication,” and you can justify a rational choice for any patient in the exam — and in the clinic.