The current status of calcium antagonists in cardiovascular therapy
Chia, B.L.; Ee, B.K.; Tan, A.T.; Choo, M.
Singapore Medical Journal 23(2): 121-127
1982
ISSN/ISBN: 0037-5675 PMID: 7135002 Document Number: 191789
The Ca antagonists are a group of pharmacological agents which block the influx of Ca2+ into the cells by their specific action on the slow Ca channels present on the membrane of myocardial and vascular smooth muscle cells. As a result of this action, all Ca antagonists dilate coronary arteries and the peripheral arterioles. Although all Ca antagonists depress myocardial contractility in isolated muscle preparation, this negative inotropic property is minimized in the intact circulation by their afterload reduction property. Verapamil, but no nifedipine, is highly effective in abolishing attacks of supraventricular tachycardia and is successful in this respect in about 90-100% of instances. The conversion rate for atrial fibrillation and atrial flutter is much lower, but even in those cases which do not convert to sinus rhythm the ventricular rate is considerably reduced. Both nifedipine and verapamil are highly effective in Prinzmetal's angina and are specific agents in this condition. They are also effective in Heberden's angina with an efficacy equal to that of the blockers. Nifedipine has profound hypotensive effects and nifedipine given orally or sublingually will probably emerge as the drug of choice in hypertensive emergencies. Both nifedipine and verapamil are potent hypotensive agents for the long term treatment of hypertension. The role of Ca antagonists in the treatment of hypertrophic cardiomyopathy is at present unproven. The side effects of Ca antagonists are few. The commonest side effect of oral verapamil is constipation. Because of its profound effect on the cardiovascular system it is likely that the Ca antagonists will become a very important group of drugs in the treatment of cardiovascular disorders in this decade.