Antihypertensive Drugs: Classification and Uses

Hypertension is called as sustained elevation in BP above the normal limits (120/80) and that increases the risk of organ damage. If the BP is elevated (120-129) then lifestyle modifications are advised like exercise and less salt diet. But if there is hypertension ( >130/90) then antihypertensive drugs are required. The target BP is 120/80.

Antihypertensives classification

1. Sympatholytics

These reduces the sympathetic activity by stimulation of alpha-2 receptors in the brain. It  includes :

• Central acting sympatholytic drugs
  • Clonidine
  • Alpha-methyl dopa 
• Adrenergic neuron blockers
  • Reserpine
  • Guanthidine
• Beta-blockers
  • Acts on heart and decreses Cardiac output.
  • Acts on kidney and decreases renin release.
• Alpha- blockers
• Produce vasodilation and hence lowers diastolic BP.

2. Diuretics

• Thiazides ( Na+/Cl- blockers) - Chlorothiazide, Chlorthalidone, Hydrochlorothiazide.
• Loop diuretics (Na+/K+/Cl- blockers) - Furosemide, Bumetanide and torsemide.
• Potassium sparing diuretics- Spironolactone, Eplerenone

3. RAAS Inhibitors

• ACE inhibitors
• Angiotensin Receptor Blockers
• Aliskiren

4. Calcium Channel Blockers

• Dihydropyridines- Acts on blood vessels mainly. The types are
  • Amlodipine
  • Nimodipine
  • Nicardipine
  • Nifedipine
• Non- Dihydropyridines- Diltiazem, Verapamil

5. Vasodilators like Hydralazine and  Minoxidil

Also Read: Medrol (Methylprednisolone): Uses, Side Effects, Precautions and Drug Interaction

Antihypertensives uses

1. Essential Hypertension: It is the most common type of hypertension. The anti hypertensives can be advised here are:

• The first line drugs are ACE inhibitors, CCBs and Thiazide diuretics.
• The second line drugs are Beta- blockers.
• The target BP for >60 years old is <150/90 mmHg but in all other conditions it is <140/90mmHg.

2. Unconrolled Hypertension: When BP is not controlled by 2 drugs at a maximum tolerable dose then add 3^rd drug. 

3. Resistant Hypertension: When BP is not tolerated by 3 drugs ( one of which should be a diuretic) at a maximum tolerable dose. The treatment is add spironolactone/eplerenone.

4. Refractory Hypertension: When BP is not controlled by 5 drugs together( Including a long acting thiazide like diuretic and a mineralocorticoid receptor antagonist) at a maximum tolerable dose.

The treatment in this scenario is Sympathectomy.

5. Hypertension with comorbidity:

• The ACE inhibitors are given if patient is having hypertension and the following diseases:
  • Chronic kidney disease ( Microalbuminurea and ESRD)
  • Diabetes Mellitus
  • Metabolic Syndrome
  • Retinopathy

• The DHP type Calcium channel blockers are given if the patient has following diseases along with hypertension:
  • Peripheral Vascular Disease
  • Renal artery sclerosis
  • Atherosclerosis

• Beta blockers are given if the patient has hypertension and the following diseases:
  • Stable angina
  • Hypertrophic Obstructive Cardiomyopathy
  • Aortic dissection
  • Atrial fibrillation
  • Migraine

• Prazosin (Alpha-1 blocker) is given if the patient has Benign Prostatic Hypertrophy. It relaxes the urinary sphincter.
• Thiazide diuretics are given if the patient is hypertensive and has Osteoporosis. It preserves calcium from urine.
• Clonidine is given if the patient is having Postmenopausal Hot flashes.
• Hyperaldosteronism Is treated with spironolactone.
• Phenoxybenzamine, which is an alpha blocker,is given for Pheochromocytoma.
• There is a reaction called as cheese reaction which occurs on clonidine withdrawl and the drug of choice is Phentolamine.

6. Hypertension in pregnancy: There are lot of drugs like Spironolactone, ACE inhibitors (Renal agenesis) , diuretics (Placental Ischemia) , NItroprusside (Cyanide toxicity) etc which are unsafe to use in Pregnancy because of their Teratogenic action. But there are few drugs which are approved for usage in the Pregnancy. The mnemonic for approved drugs is LHMC.

• Labetolol ( drug of choice)
• Hydralazine
• Methyldopa
• CCB like Nifedipine
• For chronic Hypertension in pregnancy, Alpha Methyldopa is the safest.

7. Hypertensive crisis is a condition in which the BP of the patient is more than 180/120mmHg. The drug of choice is Nicardipine.

Also Read: Cetrizine: Uses, Side Effects, Precautions And Drug Interaction

Important topics in Pharmacology for NEET-PG

Antihypertensive Drugs Contraindications

• Loop and thiazide diuretics are contraindicated in GOUT.
• ACE inhibitors/ARBs are contraindicated in Hyperkalemia, renal artery stenosis and pregnancy.
• Spironolactone is contraindicated in Hyperkalemia.
• Beta blockers are not given in patient with Asthma or COPD.
• Beta blockers, Verapamil and Diltiazem is not given in patient with Bradycardia.

Also Read: Pantoprazole: Uses, Procedure, Precautions, Drug Interaction and Side Effects