Verapamil, calcium channel blocking vasodilator effect

Nifedipine (a dihydropyridine) Block of vascular L-type calcium channels > cardiac channels Like verapamil and diltiazem less cardiac effect Prophylaxis of angina, hypertension Oral, duration 4-6 h Toxicity Excessive hypotension Interactions Additive with other vasodilators... 

Four categories of calcium channel blockers can be defined based on their chemical structures and actions diphenylalkylamines, benzothiazepines, dihydropyridines, and bepridil. Both diphenylalkylamines (verapamil) and benzothiazepines (diltiazem) exhibit effects on both cardiac and vascular tissue. With specificity for the heart tissue, these two types of calcium channel blockers can slow conduction through the AV node and are useful in treating arrhythmias. The dihydropyridines (nifedipine is the prototypical agent) are more potent peripheral and coronary artery vasodilators. They do not affect cardiac conduction, but can dilate coronary arteries. They are particularly useful as antianginal agents. Bepridil is unique in that it blocks both fast sodium channels and calcium channels in the heart. All calcium channel blockers, except nimodipine and bepridil, are effective in treating HTN. 

Calcium channel antagonists enhance vasodilation by blocking L-type Ca2+ channels in cardiac and vascular tissues. They are particularly effective for elderly and African American patients. Drugs considered are verapamil, diltiazem, nifedipine, and nimodipine. 

Calcium antagonists (Figure 4.3) are agents which block the flow of calcium ions into cardiac and vascular smooth muscle when they are stimulated to contract. They have value as vasodilators for use in hypertension and also reduce blood flow resistance and cardiac workload in the treatment of angina. Verapamil (Knoll Pfizer, 1967) is also used as an antiarrhythmic because of its effects on ion channels in the heart s electrical conduction system. Nifedipine (Bayer, 1977) is among the world s top 25 drugs and is the forerunner of several agents of the dihydropyridine class. 

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