Calcium channel blockers work by blocking voltage-dependent calcium channels. Since these channels are concentrated in sinoatrial nodes (SA node) and atrioventricular nodes (AV node), this drug class helps by decreasing conduction through the AV node. This mechanism explains why these drugs are contraindicated in heart block, especially 2nd degree block and complete heart block.
Calcium channels are also in the smooth muscle of vasculature and blocking them allows blood vessels to dilate. This action allows these medications to be effective in treating angina pectoris.
These medications act to decrease blood pressure and are effective in essential hypertension. Blood pressure is lowered by dilation of the arterioles. Verapamil is a first-line medication for treating chronic hypertension.
These drugs are effective in treating arrhythmias, especially atrial tachyarrhythmias, as they slow impulse conduction through the AV node. Calcium channel blockers are considered class IV antiarrhythmic medications.
Bradycardia or slowed heart rate can develop with these medications, as they work to slow impulse conduction through the AV node to the ventricles.
By blocking calcium channels and consequentially relaxing smooth muscle in vasculature, these medications can lead to the side effect of hypotension.
Calcium channel blockade in this drug class leads to decreased smooth muscle motility and can manifest as constipation. This occurs more often with verapamil than with diltiazem.
Peripheral edema is an annoying, common side effect of these medications. It occurs due to arteriolar dilation, leading to capillary hypertension, which causes fluid extravasation into tissues.
Verapamil is known for having the side effect of gingival hyperplasia, which is described as an enlargement and overgrowth of the gums.
It is important to provide medication education to the patients. Inform them to notify health care providers of peripheral edema, and patients should monitor swelling in ankles and feet. They should not crush or chew sustained-release oral medications. Patients should avoid grapefruit juice, as it can raise blood levels and lead to toxicity.
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