Hypertension and Antihypertensive Agents

Summary of Hypertension and Antihypertensive Agents

Hypertension, characterized by persistently elevated blood pressure, is a significant risk factor for cardiovascular diseases. Managing hypertension often involves lifestyle modifications and pharmacological interventions. This summary covers the classification, types, and complications of hypertension, along with a detailed overview of antihypertensive agents, focusing on their mechanisms of action, adverse effects, and therapeutic uses.

Classification of Hypertension

• Normal: Systolic blood pressure below 120 mmHg and diastolic blood pressure below 80 mmHg.

• Prehypertension: Systolic blood pressure between 120-129 mmHg and diastolic blood pressure below 80 mmHg.

• Hypertension Stage 1: Systolic blood pressure between 130-139 mmHg or diastolic blood pressure between 80-89 mmHg.

• Hypertension Stage 2: Systolic blood pressure 140 mmHg or higher or diastolic blood pressure 90 mmHg or higher.

• Hypertensive Crisis: Systolic blood pressure higher than 180 mmHg or diastolic blood pressure higher than 120 mmHg, requiring immediate medical attention.

Types of Hypertension

• Primary (Essential) Hypertension: Accounts for 90% of cases, with an unknown cause, often linked to genetic factors and abnormal sodium concentration in cells, leading to increased peripheral resistance (PR).

• Secondary (Symptomatic) Hypertension: Accounts for 10% of cases and is related to underlying conditions such as renal diseases causing renal ischemia (renal hypertension) or endocrine disturbances like pheochromocytoma and Conn's syndrome (primary hyperaldosteronism).

Complications of Hypertension

• Stroke: Damage to the brain due to interrupted blood supply.

• LVH, CHD, HF: Left ventricular hypertrophy, coronary heart disease, and heart failure.

• Retinopathy: Damage to the blood vessels in the retina.

• Renal Failure: Impaired kidney function.

• Peripheral Vascular Disease: Narrowing of blood vessels reducing blood flow to limbs.

Regulation of Blood Pressure

• Baroreceptor Reflex: A rapid response mechanism that adjusts blood pressure through changes in heart rate and vascular resistance.

• Renin-Angiotensin-Aldosterone System (RAAS): A hormonal system that regulates blood pressure and fluid balance through the release of renin, leading to the formation of angiotensin II and aldosterone.

Antihypertensive Agents Acting on the Heart

• β-Blockers:

  • Non-Selective (Propranolol, Sotalol): Block both β1 and β2 receptors, decreasing heart rate, force of contraction, and renin secretion. Adverse effects include bradycardia, heart block, bronchoconstriction, and altered lipid profiles. Contraindicated in patients with Type 1 Diabetes Mellitus (T1DM).

  • Selective β1-Blockers (Atenolol, Metoprolol, Bisoprolol, Nebivolol, Esmolol): Cardio-selective, useful for diabetic and asthmatic patients.

  • β1, α1-Blockers (Labetalol, Carvedilol): Produce peripheral vasodilation and are used in pregnancy-induced hypertension.

Antihypertensive Agents Acting on the Kidney

• Renin Inhibitors (Aliskiren): Selective renin inhibitor used in combined therapy. Adverse effects include gastrointestinal disturbances. Contraindicated in pregnancy.

• ACE Inhibitors (-pril):

  • Examples: Captopril, Enalapril, Fosinopril, Cilazapril, Lisinopril.

  • Mechanism: Decrease peripheral resistance without reflex increase in heart rate or contractility.

  • Adverse Effects: Dry cough, hypotension, hyperkalemia, altered taste, and angioedema.

  • Advantages: No metabolic effects on cholesterol, uric acid, or blood glucose, making them suitable for diabetic patients.

• Angiotensin II Receptor Blockers (ARBs) (-sartan):

  • Examples: Losartan, Valsartan, Candesartan, Irbesartan, Telmisartan.

  • Mechanism: Competitive antagonists of angiotensin II at its receptor in blood vessels, adrenal cortex, and heart.

  • Advantages: Similar to ACE inhibitors but without the cough or angioedema.

Antihypertensive Agents Acting on Blood Vessels

• α1-Blockers (Prazosin, Terazosin, Doxazosin, Tamsulosin):

  • Mechanism: Selective α1-blockers cause vasodilation, reducing peripheral resistance. Tamsulosin is used for symptomatic treatment of benign prostatic hypertrophy (BPH).

  • Adverse Effects: Syncope (first-dose effect), orthostatic hypotension, and reflex tachycardia.

• α2-Agonists (Clonidine, α-Methyl Dopa):

  • Mechanism: Selectively increase central α2 receptors, decreasing sympathetic outflow.

  • Use: α-Methyl Dopa is safe during pregnancy.

  • Caution: Must be withdrawn gradually to avoid hypertensive crisis.

• Direct Vasodilators:

  • Calcium Channel Blockers (CCBs):

    • Examples: Nifedipine, Amlodipine, Diltiazem, Verapamil.

    • Mechanism: Block calcium channels, causing vasodilation.

    • Side Effects: Hypotension, headache, constipation, and bradycardia (Verapamil and Diltiazem).

    • Advantages: Natriuretic effect and no adverse effects on metabolic function or asthma.

  • Potassium Channel Openers (Minoxidil, Diazoxide):

    • Mechanism: Activate potassium channels, causing hyperpolarization and relaxation of smooth muscle.

    • Uses: Minoxidil for male baldness, Diazoxide for hypertensive emergencies.

    • Side Effects: Hirsutism (Minoxidil).

  • Nitric Oxide Releasing Agents:

    • Hydralazine: Arteriodilator, used orally in severe hypertension.

    • Sodium Nitroprusside: Mixed dilator, administered via IV infusion for hypertensive emergencies.

Non-Therapeutic Management of Hypertension

• Lifestyle Modification: Weight loss, restriction of alcohol and smoking, reduced salt intake, and regular exercise. These measures can restore normal blood pressure in mild hypertension cases.

Conclusion

Effective management of hypertension requires a comprehensive approach, including lifestyle modifications and appropriate pharmacological interventions. Antihypertensive agents target different mechanisms to lower blood pressure, and their selection depends on individual patient characteristics and comorbidities. Understanding the classification, types, and complications of hypertension, along with the mechanisms of action and adverse effects of antihypertensive drugs, is essential for optimizing therapeutic outcomes and improving patient care.