Antihypertensive Drugs and it's classification | Pharmacology Notes Antihypertensive agent

 Hypertension 

Hypertension is a disease characterised by abnormally high blood pressure.
Antihypertensive drugs, AMLODIPINE, LOSARTAN,




Classification of Hypertension

1.  Primary hypertension for which the exact cause is not known.
2.  Secondary hypertension which may be due to renal , endocrine or vascular lesions.

Irrespective of the cause , hypertension is harmful . It may lead to degenerative changes in cerebral , coronary , renal and retinal tissues. Antihypertensive drugs are helpful in the treatment of hypertension.

Classification of Antihypertensive Drugs

1.  ACE inhibitors  - 

Captopril , Enalapril , Lisinopril , Ramipril

2.  Angiotensin antagonist -

Losartan

3.  Calcium channel blockers - 

Nifedipine , Felodipine , Amlodipine , Verapamil , Diltiazem 

4.  Diuretics - 

Hydrochlorothiazide , Frusemide , Indapamide , Spironolactone , Triamterene , Amiloride

5.  Beta adrenergic blockers -

Propranolol , Metoprolol , Atenolol

6.  Alpha adrenergic blockers -

Prazocin , Terazocin , Phentolamine

7.  Central sympatholytis -

Clonidine , Methyldopa

8.  Vasodilator -

Hydralazine , Minoxidil , Diazoxide

ACE inhibitors

CAPTOPRIL :

It acts by inhibiting angiotensin converting enzyme (ACE). This prevents the conversion of angiotensin I to angiotensin II. It is effective in all types of hypertension. But marked effect occurs in renovascular hypertension. 

Adverse reactions - 

(1)  Renal damage  
(2)  Hyperkalemia
(3)  Impairment of immune response
(4)  loss of taste sensation
(5)  Dry persistent cough

ENALAPRIL :

It is an ACE inhibitor like captopril. It is more potent. Also it has a slower but longer effects. It acts by getting converted into enalaprilic acid. It can produce urticaria and angioneurotic oedma.

Anginotensin Antagonist -

LOSARTAN :

It is a competitive Antagonist of anginotensin II. It blocks all the action of anginotensin II like 
1. Vasoconstriction.
2. Central and peripheral sympathetic stimulation.
3. Release of aldosterone and adrenaline.

The antihypertensive effey of LOSARTAN lasts for 24 hours. It doesn't alter heart rate or cardiovascular reflexes. It is well absorbed orally and it undergoes first pass metabolism in the liver.

Adverse reactions :

Hypotension , hyperkalemia , fetal toxicity , weakness and dizziness.

Calcium channel blockers -

The contractility of cardiac and vascular smooth muscle is dependent on extracellular calcium concentration. The Calcium channel blockers interfere with the entry of calcium into myocardial and vascular smooth muscle. This decreases the availability of intracellular calcium.

NIFEDIPINE :

It is a dihydropyridine derivative . It is a calcium channel blockers used for the treatment of hypertension and angina pectoris . The essential action is arteriolar dilatation . This decreases total peripheral resistance leading to fall in BP. It also has mild natriuretic action without significant diuresis .

Adverse reactions :

Palpitations , flushing , ankle edema , hypotension , headache , drowsiness and nausea.

FELODIPINE -

It differs from nifedipine in that it has
1. Selective distribution in vascular tissue.
2. Larger tissue distribution.
3. Longer half life.

AMLODIPINE -

It is also a dihydropyridine Calcium channel blocker. It's advantage are 
1. It is slowly but completely absorbed on oral administration .
2. Early vasodilator side effects like Flushing and palpitations can be avoided .
3. Oral bioavailability is high .

Vasodilators -

HYDRALAZINE :

Hydralazine is a hydrazine derivative. It is an inhibitor of MAO . But there is no correlation between this effect and hypotensive action .

Mechanism of action :

It has an agonistic effect on beta adregenic receptors . Because of this it produces vasodilation accompanied by tachycardia and increased cardiac output . It also acts by depressing the vasomotor centre.

Adverse reactions :

Headache , nausea , weakness , palpitation , flushing , and tachycardia . Also neuropathy which is reversed by pyridoxine . It also produces priopism .

DIAZOXIDE :

DIAZOXIDE is chemically related to chlorothiazide . But it is not a diuretic . It is a powerful hypotensive effect which is due to direct arteriolar dilation. It produce an immediate effect which lasts for 12 hours . It also has a potent hyperglycemia effect .



                                    

                                       

                                       

                                                          

                                                         

                                                      

                                      


                                        
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