Thursday, March 17, 2011

Calcium entry blockers

Much of the calcium entry blockers are dihydropyridines.

Clacium entry blockers include Amlodipine, Bepridil, Diltiazim, Felodipine, Isradipine, Nicardipine, Nifedipine, Nimodipine, Nisoldipine, Nitrendipine, Verapamil

Mechanism of action:

They get bind to receptors present on L-type calcium channels (voltage gated calcium channels) resulting in the blockage of calcium channels in the heart and in the smooth muscles of the coronary and peripheral vessels. This causes inhibition of calcium inflow to the cardiac and smooth muscle cells resulting in relaxation of muscles.

Actions:

Calcium channel blockers cause relaxation of the arterioles and veins but relaxation is more pronounced in arterioles than in the veins.

Calcium channel blockers causes dilatation of the coronary arterioles and coronary arteries and reduction of coronary artery spasm. This results in elevated oxygen supply to the muscles of the heart in patients with variant angina.

On the other hand, dilatation of the peripheral arterioles causes a decrease in total peripheral vascular resistance leading to decreased blood pressure. This affect is mainly caused by nifedipine. This causes a decrease in oxygen requirement of the muscles of the heart.

All of these factors are responsible for less oxygen requirement in patients with angina:

1. Reduced generation of impulses in SA node and reduced conduction in AV node

2. Reduced cardiac contractility and output

Verapamil and diltiazim show more pronounced effects on the heart.

Verapamil blocks release of insulin.

Verapamil blocks sodium channels less effectively, so that is why it has slight local anesthetic activity.

Pharmacokinetics:
They have a half life of about 2.5-8 hours, when used orally.

Therapeutic uses:
In hypertension when accompanied by angina, diabetes and/or asthma.

They are also used for angina pectoris, hypertrophic cardiomyopathy, migraine and atherosclerosis.

Verapamil is used to treat migraine, angina and supraventricular tachyarrhythmias.

Adverse effects:
They may cause dizziness, bradycardia, cardiac arrest, hypotension, nausea, constipation (in about 10% of patients), flushing and headache.

Contraindications:
These are contraindicated in patients with
1. cardiogenic shock
2. severe hypotension
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