Classification of Drugs for Hypertension
Hypertension is managed by several classes of drugs, each with specific mechanisms, therapeutic doses, indications, adverse effects, and contraindications. This guide outlines the major categories of antihypertensive drugs.
1. Diuretics
Mechanism of Action: Diuretics increase sodium and water excretion, lowering blood volume and blood pressure.
Therapeutic Doses
- Thiazides (e.g., Hydrochlorothiazide): 12.5–25 mg once daily
- Loop Diuretics (e.g., Furosemide): 20–40 mg twice daily
- Potassium-sparing Diuretics (e.g., Spironolactone): 25–50 mg once daily
Indications
Primarily used for hypertension, especially in patients with fluid retention or heart failure.
Adverse Effects
- Electrolyte imbalance (e.g., hypokalemia with thiazides and loop diuretics)
- Dehydration, dizziness, hyperuricemia
- Hyperkalemia (with potassium-sparing diuretics)
Contraindications
Severe kidney disease, electrolyte imbalance, and sulfa allergy (for thiazides and loop diuretics).
2. Beta-Blockers
Mechanism of Action: Beta-blockers reduce heart rate and cardiac output by blocking beta-adrenergic receptors.
Therapeutic Doses
- Atenolol: 25–100 mg once daily
- Metoprolol: 50–100 mg twice daily
Indications
Used in hypertension, angina, arrhythmias, and post-myocardial infarction management.
Adverse Effects
- Bradycardia, fatigue, bronchospasm
- Cold extremities, sexual dysfunction
Contraindications
Asthma, severe bradycardia, heart block, peripheral artery disease.
3. Calcium Channel Blockers (CCBs)
Mechanism of Action: CCBs block calcium channels in vascular smooth muscle, leading to vasodilation and reduced blood pressure.
Therapeutic Doses
- Amlodipine: 5–10 mg once daily
- Verapamil: 80–120 mg three times daily
Indications
Used for hypertension, angina, and arrhythmias (especially in non-dihydropyridine CCBs).
Adverse Effects
- Peripheral edema, dizziness, constipation (especially with verapamil)
- Headache, flushing
Contraindications
Severe heart failure, certain arrhythmias (e.g., sick sinus syndrome without pacemaker).
4. ACE Inhibitors
Mechanism of Action: ACE inhibitors block the conversion of angiotensin I to angiotensin II, reducing vasoconstriction and blood pressure.
Therapeutic Doses
- Enalapril: 5–20 mg once or twice daily
- Lisinopril: 10–40 mg once daily
Indications
Used for hypertension, heart failure, and protection of kidney function in diabetes.
Adverse Effects
- Cough, hyperkalemia, angioedema
- Hypotension, dizziness
Contraindications
Pregnancy, history of angioedema, bilateral renal artery stenosis.
5. Angiotensin II Receptor Blockers (ARBs)
Mechanism of Action: ARBs block angiotensin II receptors, reducing vasoconstriction and promoting blood pressure reduction.
Therapeutic Doses
- Losartan: 50–100 mg once or twice daily
- Valsartan: 80–320 mg once daily
Indications
Used in hypertension, heart failure, and diabetic nephropathy.
Adverse Effects
- Hyperkalemia, hypotension, dizziness
Contraindications
Pregnancy, severe renal impairment, bilateral renal artery stenosis.
6. Alpha-Blockers
Mechanism of Action: Alpha-blockers relax blood vessels by blocking alpha-adrenergic receptors, lowering blood pressure.
Therapeutic Doses
- Prazosin: 1–5 mg twice daily
- Doxazosin: 1–16 mg once daily
Indications
Primarily used in hypertension with benign prostatic hyperplasia (BPH).
Adverse Effects
- Orthostatic hypotension, dizziness, fatigue
Contraindications
Severe heart conditions, certain arrhythmias.
7. Central Alpha-2 Agonists
Mechanism of Action: These drugs stimulate alpha-2 receptors in the brain, reducing sympathetic outflow and lowering blood pressure.
Therapeutic Doses
- Clonidine: 0.1–0.3 mg twice daily
- Methyldopa: 250–500 mg twice daily
Indications
Primarily used in resistant hypertension and pregnancy-induced hypertension (methyldopa).
Adverse Effects
- Drowsiness, dry mouth, sedation
Contraindications
Severe liver disease (for methyldopa), caution in patients with depression.
8. Vasodilators
Mechanism of Action: Direct vasodilators relax the blood vessels, reducing resistance and lowering blood pressure.
Therapeutic Doses
- Hydralazine: 10–50 mg four times daily
- Minoxidil: 5–40 mg once or twice daily
Indications
Used for severe hypertension, typically as a third or fourth-line treatment.
Adverse Effects
- Fluid retention, reflex tachycardia, excessive hair growth (minoxidil)
Contraindications
Severe heart disease, caution in patients with a history of stroke.