Calcium channel blockers. Potential medical benefits and side effects.

Calcium channel blockers are recently developed antihypertensive drugs. In terms of mechanisms of action, their specificity is not so well established as that of angiotensin converting enzyme inhibitors but is better understood than that for diuretics or adrenergic-inhibiting drugs. Calcium channel blockers were originally developed for treatment of angina but were found to lower arterial pressure as well. Three of them are now in wide use in the United States; their therapeutic spectrum in regard to type of hypertension is broad. Sublingual nifedipine has replaced intravenously administered vasodilators as immediate treatment of severe hypertension, and all three drugs, given orally, have been shown to be effective in mild, moderate, and severe hypertension. The three drugs available in this country are verapamil, diltiazem, and nifedipine. Pharmacological studies have shown that verapamil has the most negative chronotropic and inotropic effects of the three, with nifedipine producing the most vasodilation and having the potential for causing reflex tachycardia. Actually in practice, these various pharmacological differences have proved to have less significance than previously thought, and the drugs seem to have about equal antihypertensive effectiveness. Comparisons of calcium entry blockers with other drugs have shown them to be equally effective in whites as propranolol but more effective in blacks. Responsiveness appears to be related, as well, to pretreatment plasma renin activity and age. Thus, the antihypertensive effect is directly related to age and inversely related to plasma renin activity. The side effects mostly relate to vasodilation, reflex tachycardia, palpitations, headache, and edema; they are not frequent, and the drugs are well tolerated.