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Calcium channel blockers

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Main article: Channel blockers

Calcium channel blockers are a class of drugs with effects on many excitable cells of the body, like the muscle of the heart, smooth muscles of the vessels or neuron cells. The latter are used as antiepileptics and are not covered in this article.

The main action of calcium channel blockers is to lower the blood pressure. It is for this action that it is used in individuals with hypertension.

Explanation

Most calcium channel blockers decrease the force of contraction of the myocardium (muscle of the heart). This is known as the negative inotropic effect of calcium channel blockers. It is because of the negative inotropic effects of most calcium channel blockers that they are avoided (or used with caution) in individuals with cardiomyopathy.

Many calcium channel blockers also slow down the conduction of electrical activity within the heart, by blocking the calcium channel during the plateau phase of the action potential of the heart (see: cardiac action potential). This causes a lowering of the heart rate and may cause heart blocks. This is known as the negative chronotropic effect of calcium channel blockers. The negative chronotropic effects of calcium channel blockers make them a commonly used class of agents in individuals with atrial fibrillation or flutter in whom control of the heart rate is an issue.

Mechanism of action

Calcium channel blockers work by blocking L-type voltage gated calcium channels (VGCC) in the heart and in the blood vessels. This prevents calcium levels from increasing as much in the cells when stimulated, leading to less contraction.

This decreases total peripheral resistance by dilating the blood vessels, and decreases cardiac output by lowering the force of contraction. Because resistance and output drop, so does blood pressure.

With low blood pressure, the heart does not have to work as hard; this can ease problems with cardiomyopathy and coronary disease.

Unlike with beta-blockers, the heart is still responsive to sympathetic nervous system stimulation, so blood pressure can be maintained more effectively.

List of calcium channel blockers

Dihydropyridine calcium channel blockers often used to reduce systemic vascular resistance and arterial pressure, but is not used to treat angina because the vasodilation and hypotension can lead to reflex tachycardia. This CCB class is easily identified by the suffix "-pine".

Phenylalkylamine calcium channel blockers are relatively selective for mycardium, reduces myocardial oxygen demand and reverses coronary vasospasm and is often used to treat angina. It has minimal vasodilatory effects compared with dihydropyridines.

Benzothiazepine calcium channel blockers is an intermediate class between phenylalkylamine and dihydropyridines in its selectivity for vascular calcium channels. By having both cardiac depressant and vasodilator actions, benzothiazepines are able to reduce arterial pressure without producing the same degree of reflex cardiac stimulation caused by dihydropyridines.

Other

Other drugs with similar uses

Other classes of pharmaceutical agents that have overlapping effects as calcium channel blockers include ACE inhibitors, beta-blockers, and nitrates.

See also


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