Thursday, August 23, 2007

Calcium channel blockers

Mechanism of action

Calcium channel blockers have a negative inotropic effect - they decrease the force of contraction of the myocardium.

They block L-type voltage gated calcium channels in the heart and blood vessels. This prevents calcium levels from increasing as much in the cells when stimulated, leading to less contraction.

They also decrease total peripheral resistance by dilating the blood vessels, and decreasing 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.

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. This causes a lowering of the heart rate and may cause heart blocks (negative chronotropic effect) of calcium channel blockers.


There are 2 classes of CCBs:
  1. Dihydropyridines

    • Used to reduce systemic vascular resistance and arterial pressure, but are 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" e.g. Amlodepine, Felodipine.

  2. Non-dihydropyridines

    • Relatively selective for myocardium, reduce myocardial oxygen demand and reverse coronary vasospasm, and are often used to treat angina.
    • They have minimal vasodilatory effects compared with dihydropyridines.
    • Action is intracellular.
    • E.g. verapamil.


  • Atrial fibrillation or flutter - to control heart rate via negative chronotropic effect.


  • Avoided (or used with caution) in individuals with cardiomyopathy due to negative inotropic effect.
  • Non-dihydropyridine CCBs should not be combined with beta-blockers because they are both negative inotropes and affect the AV node.
  • Wikpedia,

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