Calcium channel blockers

Calcium channel blockers

Calcium channel blockers are commonly used to prevent angina that doesn’t respond to drugs in either of the other antianginal classes. They’re the drug of choice to treat Prinzmetal’s angina. As mentioned earlier, several of the calcium channel blockers are also used as antiarrhythmics and to treat hypertension. Calcium channel blockers used to treat angina include:

• amlodipine
• diltiazem
• nicardipine
• nifedipine
• verapamil.

Now I get it!

How calcium channel blockers work

Calcium channel blockers increase the myocardial oxygen supply and slow the heart rate. Apparently, the drugs produce these effects by blocking the slow calcium channel. This action inhibits the influx of extracellular calcium ions across both myocardial and vascular smooth muscle cell membranes. Calcium channel blockers achieve this blockade without changing serum calcium concentrations.

No calcium = dilation

This calcium blockade causes the coronary arteries (and, to a lesser extent, the peripheral arteries and arterioles) to dilate, decreasing afterload and increasing myocardial oxygen supply.

Pharmacokinetics

When administered orally, calcium channel blockers are absorbed quickly and almost completely. Because of the first-pass effect, however, the bioavailability of these drugs is much lower. The calcium channel blockers are highly bound to plasma proteins.

Gone without a trace

All calcium channel blockers are metabolized rapidly and almost completely in the liver.

 

Pharmacodynamics

Calcium channel blockers prevent the passage of calcium ions across the myocardial cell membrane and vascular smooth-muscle cells. This causes dilation of the coronary and peripheral arteries, which decreases the force of the heart’s contractions and reduces the workload of the heart.

The relaxation response

Also, by preventing arterioles from constricting, calcium channel blockers reduce afterload. Decreasing afterload further decreases the oxygen demands of the heart.

Rate reductions

Some calcium channel blockers (diltiazem and verapamil) also reduce the heart rate by slowing conduction through the SA and AV nodes. A slower heart rate reduces the heart’s need for additional oxygen.

 

Pharmacotherapeutics

Calcium channel blockers are used for long-term prevention of angina only, not short-term relief of chest pain. Calcium channel blockers are particularly effective for preventing Prinzmetal’s angina.\

 

Drug interactions

• Calcium salts and vitamin D reduce the effectiveness of calcium channel blockers.
• Nondepolarizing blocking drugs may have an enhanced muscle-relaxant effect when taken with calcium channel blockers.
• Verapamil and diltiazem increase the risk of digoxin toxicity, enhance the action of carbamazepine, and may cause myocardial depression.

Warning!

Adverse reactions to calcium channel blockers

As with other antianginal drugs, cardiovascular reactions are the most common and serious adverse reactions to calcium channel blockers. These include orthostatic hypotension (a drop in blood pressure when a person stands up), heart failure, and hypotension. Diltiazem and verapamil can cause such arrhythmias as bradycardia, sinus block, and atrioventricular block.

Others

Other possible adverse reactions include dizziness, headache, flushing, weakness, and persistent peripheral edema.