Calcium antagonists, also known as calcium entry blockers or calcium channel blockers, act by blocking the movement of calcium into cells. The cells respond less briskly and so use less oxygen. The supply-demand equation is also improved by the vessel-dilating effect of calcium antagonists. “Afterload” is reduced when peripheral vessels are widened and more blood may reach the heart muscle because coronary vessels are relaxed. Calcium antagonists also relieve spasm and are often used for Prinzmetal’s angina.
Unlike beta-blockers there is no proof that calcium antagonists reduce mortality even though they do reduce angina. Therefore they are not your doctor’s first choice. They may be added to beta-blockers and nitrates to form “triple therapy” for angina that is hard to control.
Calcium antagonists are a diverse group of medicines and while they are generally easier to tolerate than beta-blockers, they do have their side effects. Verapamil (Calan, Isoptin, Verelan) can make heart failure worse, is rarely given in combination with beta-blockers, and is famous for causing constipation. Nifedipine (Adalat, Procardia), is-radipine (DynaCirc), and nicardipine (Cardene) form a group more likely to cause dizziness, flushing, headaches, rapid heartbeat, and swelling of the feet. Amlodipine (Norvasc) also causes headache and dizziness in some people. Diltiazem (Cardizem, Dilacor) can cause any of these problems but is often the best tolerated of the class.
Long-acting formulations of these drugs, taken once or twice a day, are safer than the fast-acting forms as well as more convenient. Be especially careful to store these drugs out of reach of children as they can cause swift death in young children even when only a few are swallowed.
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