Classification of Antihypertensive Drugs

Classification of Antihypertensive Drugs: Complete Guide for Pharmacy Students

High blood pressure (hypertension) is one of the leading risk factors for cardiovascular diseases such as stroke, myocardial infarction, heart failure, and chronic kidney disease. Antihypertensive drugs help reduce blood pressure by acting through different mechanisms, including reducing blood volume, relaxing blood vessels, decreasing cardiac output, or inhibiting the renin-angiotensin-aldosterone system (RAAS).

Understanding the classification of antihypertensive drugs is essential for pharmacy students preparing for Nepal Pharmacy Council (NPC), Lok Sewa, B.Pharm, D.Pharm, and M.Pharm entrance examinations.

Classification of Antihypertensive Drugs

Antihypertensive drugs are broadly classified into five major groups:

Diuretics
Renin-Angiotensin System (RAS) Inhibitors
Sympathetic Inhibitors
Calcium Channel Blockers (CCBs)
Vasodilators

1. Diuretics

Diuretics lower blood pressure by increasing sodium and water excretion, thereby reducing blood volume and cardiac output.

A. Thiazide Diuretics

Examples

Hydrochlorothiazide
Chlorthalidone
Indapamide

Mechanism of Action

Inhibit Na⁺/Cl⁻ cotransporter in the distal convoluted tubule.
Increase sodium and water excretion.
Long-term use decreases peripheral vascular resistance.

Clinical Uses

First-line treatment of hypertension
Mild edema
Heart failure

Important Adverse Effects

Hypokalemia
Hyperuricemia
Hyperglycemia
Hyponatremia

B. High Ceiling (Loop) Diuretics

Examples

Furosemide
Bumetanide
Torsemide

Mechanism

Inhibit Na⁺-K⁺-2Cl⁻ transporter in the loop of Henle.
Produce powerful diuresis.

Uses

Hypertension with renal impairment
Pulmonary edema
Congestive heart failure

Adverse Effects

Hypokalemia
Ototoxicity
Dehydration

C. Potassium-Sparing Diuretics

Examples

Spironolactone
Eplerenone
Amiloride

Mechanism

Aldosterone antagonists (Spironolactone, Eplerenone)
ENaC blocker (Amiloride)

Advantages

Prevent potassium loss
Useful in resistant hypertension

Adverse Effects

Hyperkalemia
Gynecomastia (Spironolactone)

2. Renin-Angiotensin System (RAS) Inhibitors

These drugs inhibit the RAAS pathway responsible for vasoconstriction and sodium retention.

A. ACE Inhibitors

Examples

Captopril
Enalapril
Lisinopril
Ramipril
Perindopril
Quinapril
Fosinopril
Trandolapril

Mechanism

Block conversion of Angiotensin I to Angiotensin II.
Increase bradykinin levels.
Cause vasodilation.

Clinical Uses

Hypertension
Heart failure
Diabetic nephropathy
Post-myocardial infarction

Adverse Effects

Dry cough
Hyperkalemia
Angioedema
Contraindicated in pregnancy

B. Angiotensin II (AT₁) Receptor Blockers (ARBs)

Examples

Losartan
Valsartan
Candesartan
Telmisartan
Irbesartan
Olmesartan

Mechanism

Block AT₁ receptors.
Prevent vasoconstriction and aldosterone secretion.

Advantages

Similar efficacy to ACE inhibitors
No bradykinin-induced cough

Adverse Effects

Hyperkalemia
Hypotension
Contraindicated during pregnancy

C. Direct Renin Inhibitor

Example

Aliskiren

Mechanism

Directly inhibits renin activity.
Prevents formation of Angiotensin I.

Uses

Essential hypertension

Adverse Effects

Hyperkalemia
Diarrhea
Hypotension

3. Sympathetic Inhibitors

These drugs decrease sympathetic nervous system activity, reducing heart rate, cardiac output, and vascular resistance.

A. β-Adrenergic Blockers (Beta Blockers)

Examples

Propranolol
Atenolol
Metoprolol

Mechanism

Block β₁ receptors in the heart.
Decrease heart rate and cardiac output.
Reduce renin secretion.

Uses

Hypertension
Angina
Arrhythmias
Heart failure (selected agents)

Adverse Effects

Bradycardia
Fatigue
Bronchospasm (non-selective agents)

B. α + β Adrenergic Blockers

Examples

Labetalol
Carvedilol

Mechanism

Block both α and β receptors.
Reduce heart rate and peripheral resistance.

Uses

Hypertensive emergencies
Heart failure
Pregnancy-induced hypertension (Labetalol)

C. α-Adrenergic Blockers

Examples

Prazosin
Terazosin
Doxazosin
Phentolamine
Phenoxybenzamine

Mechanism

Block α₁ receptors.
Cause vasodilation.

Uses

Hypertension
Benign prostatic hyperplasia (BPH)

Adverse Effects

Orthostatic hypotension
Dizziness
First-dose syncope

D. Central Sympatholytics

Examples

Clonidine
Methyldopa

Mechanism

Stimulate central α₂ receptors.
Reduce sympathetic outflow.

Uses

Resistant hypertension
Hypertension during pregnancy (Methyldopa)

Adverse Effects

Sedation
Dry mouth
Rebound hypertension (Clonidine)

4. Calcium Channel Blockers (CCBs)

Calcium channel blockers inhibit L-type calcium channels, causing vasodilation and reduced myocardial contractility.

A. Phenylalkylamine

Example

Verapamil

Characteristics

Greater effect on the heart
Used in hypertension and arrhythmias

B. Benzothiazepine

Example

Diltiazem

Characteristics

Intermediate effect on heart and blood vessels

C. Dihydropyridines

Examples

Amlodipine
Nifedipine
Felodipine
Nicardipine
Lercanidipine
Lacidipine
Benidipine

Characteristics

Predominantly vasodilators
Common first-line antihypertensive drugs

Adverse Effects

Peripheral edema
Flushing
Headache
Reflex tachycardia (short-acting agents)

5. Vasodilators

These drugs directly relax vascular smooth muscle.

A. Arteriolar Dilators

Examples

Hydralazine
Minoxidil
Diazoxide

Mechanism

Dilate arterioles.
Reduce peripheral vascular resistance.

Uses

Resistant hypertension
Hypertensive emergencies (Hydralazine)

Adverse Effects

Reflex tachycardia
Fluid retention
Hypertrichosis (Minoxidil)
Drug-induced lupus (Hydralazine)

B. Arteriolar and Vasodilator

Example

Sodium Nitroprusside

Mechanism

Releases nitric oxide (NO).
Dilates both arteries and veins.

Uses

Hypertensive emergencies
Acute heart failure

Important Adverse Effect

Cyanide toxicity during prolonged infusion

Summary Table

Class	Main Examples	Mechanism
Thiazide Diuretics	Hydrochlorothiazide, Chlorthalidone	Increase sodium and water excretion
Loop Diuretics	Furosemide	Potent diuresis
Potassium-Sparing Diuretics	Spironolactone, Amiloride	Prevent potassium loss
ACE Inhibitors	Enalapril, Ramipril	Block Angiotensin I → II conversion
ARBs	Losartan, Telmisartan	Block AT₁ receptors
Direct Renin Inhibitor	Aliskiren	Inhibits renin
Beta Blockers	Atenolol, Metoprolol	Reduce heart rate and renin release
Alpha Blockers	Prazosin	Vasodilation
Central Sympatholytics	Clonidine, Methyldopa	Reduce sympathetic outflow
Calcium Channel Blockers	Amlodipine, Verapamil, Diltiazem	Block calcium channels
Vasodilators	Hydralazine, Minoxidil, Nitroprusside	Direct vascular smooth muscle relaxation

High-Yield Exam Points

Thiazide diuretics are considered first-line drugs for uncomplicated hypertension.
ACE inhibitors commonly cause a dry cough due to increased bradykinin.
ARBs do not usually cause cough and are suitable alternatives when ACE inhibitors are not tolerated.
Spironolactone may cause gynecomastia and hyperkalemia.
Methyldopa and Labetalol are preferred antihypertensive drugs during pregnancy.
Amlodipine is one of the most commonly prescribed calcium channel blockers for hypertension.
Sodium nitroprusside is mainly used for hypertensive emergencies.
Hydralazine may cause drug-induced lupus erythematosus.
Minoxidil can cause hypertrichosis (excessive hair growth).
Aliskiren is the only clinically used direct renin inhibitor.

Antihypertensive drugs are classified based on their mechanism of action into diuretics, RAS inhibitors, sympathetic inhibitors, calcium channel blockers, and vasodilators. A clear understanding of their classification, mechanisms, examples, clinical uses, and adverse effects is essential for pharmacy practice and competitive examinations such as the Nepal Pharmacy Council License Exam, Lok Sewa, D.Pharm, B.Pharm, and M.Pharm entrance exams.