It may be noted that ‘Ion-channel’ in cell refers to a particular protein in the cell that permits and controls inflow of ionic elements across the cell membrane.
The Calcium-channel blockers are very often used as antihypertensive agents besides their specific anti-ischaemic use. Amongst the available Calcium-channel blockers, the Dihydropyridine-derivatives viz., ‘Nifedipine’, ‘Nicardipine’, and Amlodipine’ are considered most suitable as hypotensive drugs.
Mode of action .Contraction of the vascular smooth muscle is dependent on the intra-cellular free Ca++ (Calcium ions). The inhibition of transmural movement of Calcium ions decreases the total amount of intra-cellular Ca++and thereby causes relaxation of the arteriolar smooth muscles and decrease of peripheral resistance. The result is lowering of blood pressure.
Nifedipine, Nicardipine and Amlodipine are much similar in respect of general pharmacological properties and therapeutic indications. As antihypertensive as well as antianginal, these are useful therapeutic agents. Any one of these three Dihydropyridine’ derivatives can be used in mild or moderate hypertension with or without stable angina pectoris. There is possibility of reflex tachycardia due to the peripheral visodilatory effect.
ADVERTISEMENTS:
But Amlodipine is claimed to be free from such side-effect. And, the Dihydropyridine derivatives are unlikely to cause bardycardia or heart block (in contrast to the Calcium channel blockers like ‘Verapamil’ or even ‘Dilitazem) These drugs arc unlikely to cause any significant effect on the S.A. node or the conductive system of the heart. Nifedipine (e.g.. Nicardia’, ‘Cardules’) has been in therapeutic use in hypertension and/or myocardial ischaemia for a considerable period and is also available as slow release sustained action tablets with convenient dosage schedule. And, the Nifedipine capsule pricked to allow sub-lingual absorption in sudden rise of blood pressure to an alarming level ( hypertensive crisis’) has an additional therapeutic advantage.
But, at present, Amlodipine (e.g., ‘Amloguard’, ‘Amlopress’) has become the drug of choice in hypertension with or without cardiac ischaemia because of the convenient dosage (once or twice daily) and absence of the possibility of reflex tachcardia or interference with the conductive system.
Side-effects : Headache, Hushing, palpitation, tachycardia, dizziness are common side-effects. Sometimes, peripheral oedema may also occur with Calcium-channel blockers.
Contra indications . These drugs should not be used in cases of congestive cardiac failure or Sino-Atrial and Atrio-Ventricular blocks.
ADVERTISEMENTS:
Comments :
Calcium channel blockers like Amlodipine or Nifedipine are generally considered safe effective hypotensive agents and are beneficial in patients with cardiac ischaemia. Alone, it may be effective in mild or moderate grades of hypertension. In cases of even severe grade of hypertension, appropriate combination with some other suitable hypotensive agent e.g., Thiazide diuretic. Beta-blocker or ACE-inhibitor may be found therapeutically useful.
These are ideal hypotensive in patients with bronchial asthma, diabetes mellitus, myocardial ischeamia, impaired renal function. Moreover, these do not alter the serrum lipids, glucose, uric acid or electrolytes.