A drug that blocks the entry of calcium into
the muscle cells of the heart and the arteries. It is the entry of calcium into
these cells that causes the heart to contract and arteries to narrow. By blocking
the entry of calcium, calcium channel blocker (CCBs) decrease the contraction of
the heart and dilate (widen) the arteries. By dilating the arteries, CCBs reduce
the pressure in the arteries. This makes it easier for the heart to pump blood,
and, as a result, the heart needs less oxygen. By reducing the heart's need for
oxygen, CCBs prevent or relieve angina. CCBs also are used for treating high blood
pressure because of their blood pressure-lowering effects. CCBs also slow the rate
at which the heart beats and are therefore used for treating certain abnormal heart
rhythms such as atrial fibrillation.
The most common side effects of CCBs are constipation, nausea, headache, rash,
edema (swelling of the legs with fluid), low blood pressure, drowsiness, and dizziness.
When diltiazem or verapamil are given to individuals with heart failure, symptoms
of heart failure may worsen because these drugs reduce the ability of the heart
to pump blood.
Most of the interactions of CCBs occur with verapamil or diltiazem. The interaction
occurs because verapamil and diltiazem decrease the elimination of a number of drugs
by the liver. Through this mechanism, verapamil and diltiazem may reduce the elimination
and increase the blood levels of carbamazepine (Tegretol), simvastatin (Zocor),
atorvastatin (Lipitor), and lovastatin (Mevacor). This can lead to toxicity from
these drugs.
The CCBS that have been approved for use in the US include nisoldipine (Sular),
nifedipine (Adalat, Procardia), nicardipine (Cardene), bepridil (Vascor), isradipine
(Dynacirc), nimodipine (Nimotop), felodipine (Plendil), amlodipine (Norvasc), diltiazem
(Cardizem), and verapamil (Calan, Isoptin).
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