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

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

Non-dihydropyridines:

• 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