What are CCBs and how do they work?
Calcium channel blockers are a class of drugs
that block 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, CCBs decrease
contraction of the heart and dilate (widen) the arteries.
In order to pump blood, the heart needs oxygen.
The harder the heart works, the more oxygen it requires. Angina (heart pain)
occurs when the supply of oxygen to the heart is inadequate for the amount of
work the heart must do. 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 relieve or prevent 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 types
of abnormally rapid heart rhythms.
For what conditions are CCBs used?
CCBs are used for treating high blood pressure,
angina, and abnormal heart rhythms (e.g., atrial fibrillation). They also may be
used after a heart attack, particularly among patients who cannot tolerate
beta-blocking drugs, have atrial fibrillation, or require treatment for their
angina. (Unlike beta blockers, CCBs have not been shown to reduce mortality or
additional heart attacks after a heart attack.) CCBs are as effective as ACE
inhibitors in reducing blood pressure, but they may not be as effective as ACE
inhibitors in preventing the kidney failure of high blood pressure or diabetes.
Are there any differences among CCBs?
CCBs differ in their duration of action, the
process by which they are eliminated from the body, and, most importantly, in
their ability to affect heart rate and contraction. Some CCBs (e.g., amlodipine)
have very little effect on heart rate and contraction so they are safer to use
in individuals who have heart failure or bradycardia (a slow heart rate).
Verapamil and diltiazem have the greatest effects on the heart and reduce the
strength and rate of contraction. Therefore, they are used in reducing heart
rate when the heart is beating too fast.
What are the side effects of CCBs?
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.
With which drugs do CCBs interact?
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.
What CCBs are available?
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