Antihypertensive Drugs: Complete Clinical Pharmacology Guide
Structured, accurate, and exam-focused medical reference
1. Introduction
Hypertension is a chronic elevation of arterial blood pressure that increases the risk of stroke, myocardial infarction, heart failure, and chronic kidney disease.
Blood pressure is determined by:
- Cardiac output
- Systemic vascular resistance
- Blood volume
BP = CO × SVR
Antihypertensive drugs act by reducing one or more of these factors.
2. Diuretics
Diuretics reduce blood pressure by increasing sodium and water excretion from the kidneys, thereby decreasing plasma volume and cardiac output.
Classification
- Thiazide diuretics – Hydrochlorothiazide, Chlorthalidone, Indapamide
- Loop diuretics – Furosemide, Bumetanide, Torsemide
- Potassium-sparing diuretics – Spironolactone, Eplerenone, Amiloride
Mechanism of Action
Increased sodium excretion → water follows sodium → reduced plasma volume → reduced cardiac output → reduced blood pressure
Clinical Uses
- First-line treatment for uncomplicated hypertension (thiazides)
- Heart failure and pulmonary oedema (loop diuretics)
- Resistant hypertension (spironolactone)
Adverse Effects
• Hypokalaemia (thiazides, loops)
• Hyperkalaemia (potassium-sparing diuretics)
• Hyponatraemia
• Hyperuricaemia (gout risk)
• Dehydration and hypotension
• Hyperkalaemia (potassium-sparing diuretics)
• Hyponatraemia
• Hyperuricaemia (gout risk)
• Dehydration and hypotension
3. ACE Inhibitors
ACE inhibitors block conversion of Angiotensin I to Angiotensin II, reducing vasoconstriction and aldosterone secretion.
Examples
- Captopril
- Enalapril
- Lisinopril
- Ramipril
Mechanism
Angiotensin II ↓ → Vasodilation ↑ → Aldosterone ↓ → Blood pressure ↓Clinical Uses
- Hypertension
- Heart failure
- Diabetic nephropathy
- Post-MI protection
All ACE inhibitors end in -PRIL
Dry cough, hyperkalaemia, hypotension, angioedema
4. ARBs
ARBs block angiotensin II receptors (AT1), preventing vasoconstriction and aldosterone effects.
Examples
- Losartan
- Valsartan
- Candesartan
Clinical Uses
- ACE inhibitor intolerance
- Hypertension
- Diabetic kidney protection
All ARBs end in -SARTAN
5. Calcium Channel Blockers
CCBs block calcium entry into vascular smooth muscle, causing vasodilation and reduced peripheral resistance.
Examples
Dihydropyridines:- Amlodipine
- Nifedipine
- Verapamil
- Diltiazem
Clinical Uses
- Hypertension
- Angina
- Arrhythmias (non-DHP)
Most end in -DIPINE
6. Beta Blockers
Beta blockers reduce sympathetic stimulation of the heart by blocking β1 receptors.
Examples
- Atenolol
- Metoprolol
- Bisoprolol
- Propranolol
Clinical Uses
- Hypertension
- Heart failure
- Post-MI
- Angina
All end in -OLOL
Bradycardia, fatigue, bronchospasm
7. Alpha Blockers
Alpha-1 blockers cause vasodilation by blocking sympathetic vasoconstriction.
Examples
- Prazosin
- Doxazosin
- Terazosin
Clinical Uses
- Hypertension
- Benign prostatic hyperplasia (BPH)
End in -ZOSIN
First-dose hypotension, dizziness
8. Central Acting Drugs
These drugs act on the brainstem to reduce sympathetic outflow.
Examples
- Methyldopa
- Clonidine
Clinical Uses
- Pregnancy hypertension (methyldopa)
Sedation, dry mouth, rebound hypertension
9. Direct Vasodilators
Directly relax arteriolar smooth muscle causing vasodilation.
Examples
- Hydralazine
- Minoxidil
Clinical Uses
- Severe hypertension
- Hypertensive emergencies
Reflex tachycardia, fluid retention
10. Summary
| Class | Suffix | Main Effect |
|---|---|---|
| ACE inhibitors | -pril | ↓ Angiotensin II |
| ARBs | -sartan | Block receptors |
| CCBs | -dipine | Vasodilation |
| Beta blockers | -olol | ↓ Heart rate |
| Alpha blockers | -zosin | Vasodilation |
