Short note for anti hypertensive drugs, give in proper format as per mbbs prof exam for a 6 mark question
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I now have sufficient information from the textbook (Katzung's Basic and Clinical Pharmacology, 16th Edition) to write a comprehensive MBBS prof exam short note. Let me compile the full answer.
SHORT NOTE: ANTIHYPERTENSIVE DRUGS
(6 Marks - MBBS Prof Exam Format)
Definition
Antihypertensive drugs are agents used to lower elevated blood pressure (BP >140/90 mmHg) and thereby reduce the risk of cardiovascular complications such as stroke, myocardial infarction, heart failure, and renal disease.
Classification
Antihypertensive drugs are classified based on their site/mechanism of action:
1. Diuretics
- Thiazides: Hydrochlorothiazide, Chlorthalidone
- Loop diuretics: Furosemide
- Potassium-sparing: Spironolactone, Eplerenone, Amiloride
2. Drugs Acting on the Renin-Angiotensin-Aldosterone System (RAAS)
- ACE Inhibitors: Captopril, Enalapril, Lisinopril, Ramipril
- Angiotensin Receptor Blockers (ARBs): Losartan, Valsartan, Telmisartan
- Direct Renin Inhibitor: Aliskiren
3. Calcium Channel Blockers (CCBs)
- Dihydropyridines (vascular selective): Amlodipine, Nifedipine, Felodipine
- Non-dihydropyridines (cardiac + vascular): Verapamil (phenylalkylamine), Diltiazem (benzothiazepine)
4. Sympathoplegic (Adrenergic) Drugs
- Beta-blockers: Atenolol, Metoprolol, Propranolol
- Alpha-1 blockers: Prazosin, Doxazosin
- Central alpha-2 agonists: Clonidine, Methyldopa
- Alpha + Beta blocker: Labetalol, Carvedilol
- Adrenergic neuron blockers: Reserpine
5. Direct Vasodilators
- Arteriolar: Hydralazine, Minoxidil
- Arteriolar + Venular: Sodium nitroprusside (parenteral)
Mechanisms of Action
| Class | Mechanism | Result |
|---|---|---|
| Diuretics | Deplete body Na+, reduce blood volume | Reduced CO, then reduced PVR |
| ACE Inhibitors | Block conversion of Ang I → Ang II; inhibit bradykinin degradation | Reduced vasoconstriction + reduced aldosterone |
| ARBs | Block AT1 receptor | Same as ACE inhibitors but no bradykinin effect |
| CCBs | Block L-type Ca2+ channels in vascular smooth muscle/heart | Vasodilation, reduced CO (non-DHP) |
| Beta-blockers | Block β1 receptors - reduce HR, CO, and renin release | Reduced cardiac output + RAAS activity |
| Alpha-1 blockers | Block postsynaptic α1 receptors | Vasodilation, reduced PVR |
| Direct vasodilators | Relax vascular smooth muscle directly | Reduced PVR |
(CO = cardiac output; PVR = peripheral vascular resistance)
Important Adverse Effects
| Drug | Key Adverse Effects |
|---|---|
| Thiazides | Hypokalemia, hyperglycemia, hyperuricemia, hyperlipidemia |
| ACE Inhibitors | Dry cough (bradykinin), hyperkalemia, angioedema, teratogenic |
| ARBs | Hyperkalemia, teratogenic (no cough) |
| CCBs (DHP) | Ankle edema, flushing, reflex tachycardia |
| Beta-blockers | Bradycardia, bronchospasm, cold extremities, masking of hypoglycemia |
| Hydralazine | Reflex tachycardia, Na+ retention, lupus-like syndrome |
| Minoxidil | Hypertrichosis, pericardial effusion, Na+ retention |
| Clonidine | Rebound hypertension on withdrawal, sedation |
Choice of Drug in Special Situations
| Condition | Preferred Drug |
|---|---|
| Heart failure | ACE inhibitors/ARBs, Beta-blockers, Spironolactone |
| Diabetic nephropathy | ACE inhibitors / ARBs (first choice) |
| Pregnancy | Methyldopa, Labetalol, Nifedipine (hydralazine IV for emergency) |
| Hypertensive emergency | Sodium nitroprusside (IV), Labetalol (IV), Nicardipine (IV) |
| Elderly | Thiazides, CCBs |
| Ischemic heart disease | Beta-blockers, CCBs, ACE inhibitors |
| Benign prostatic hyperplasia | Alpha-1 blockers (Prazosin) |
| Isolated systolic hypertension | Thiazides, long-acting CCBs |
| Bronchial asthma/COPD | Avoid beta-blockers; use CCBs |
Combination Therapy (Polypharmacy)
Rational combinations are used when monotherapy fails (up to 40% of patients may need 2+ drugs):
- Diuretic + ACE inhibitor/ARB - complementary RAAS + volume control
- CCB + ACE inhibitor - additive BP reduction, CCB edema reduced
- Beta-blocker + Hydralazine + Diuretic - prevents reflex tachycardia and Na+ retention from vasodilators
- Triple therapy (Diuretic + CCB + ACE inhibitor/ARB) - standard for resistant hypertension
The rationale: vasodilators (e.g. hydralazine) trigger compensatory tachycardia and Na+ retention that can negate their effect; adding a beta-blocker blocks tachycardia and a diuretic prevents fluid retention - all three drugs then enhance each other's efficacy. (Katzung's Basic and Clinical Pharmacology, 16th ed.)
Summary
Antihypertensive drugs act at four main sites: kidney (diuretics), heart/sympathetics (beta-blockers, alpha-blockers), blood vessels (vasodilators, CCBs), and RAAS (ACE inhibitors, ARBs). Drug choice depends on the patient's co-morbidities, age, and tolerability. Combination therapy is often needed for adequate BP control and to counteract compensatory mechanisms.
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