calcium channel blockers
Summary
Calcium channel blockers (CCBs) inhibit L-type voltage-gated calcium channels in vascular smooth muscle and cardiac myocytes, causing vasodilation and reduced cardiac contractility/conduction. They are divided into dihydropyridines (vasoselective) and non-dihydropyridines (verapamil, diltiazem - cardioselective). Used primarily for hypertension, angina, and certain arrhythmias.
Detail
Mechanism: CCBs block L-type calcium channels, preventing calcium influx needed for smooth muscle contraction and cardiac muscle depolarization/contraction. Dihydropyridines (amlodipine, nifedipine, nicardipine) preferentially act on vascular smooth muscle causing potent vasodilation with minimal cardiac effects—used for hypertension and Raynaud's phenomenon; reflex tachycardia is a common side effect. Non-dihydropyridines (verapamil, diltiazem) act more on cardiac tissue, decreasing heart rate (negative chronotropy), contractility (negative inotropy), and AV node conduction (negative dromotropy)—used for rate control in atrial fibrillation/flutter, SVT, and angina. Verapamil has the most cardiac selectivity and is contraindicated with beta-blockers due to risk of severe bradycardia/heart block; also causes constipation. Diltiazem is intermediate between verapamil and dihydropyridines. Clinical uses include hypertension, stable/vasospastic (Prinzmetal) angina, supraventricular arrhythmias (non-DHPs), and Raynaud phenomenon (DHPs). Side effects: peripheral edema, flushing, headache, gingival hyperplasia (especially nifedipine), reflex tachycardia (DHPs); bradycardia, AV block, constipation, and negative inotropy (non-DHPs). Toxicity/overdose treated with IV calcium, glucagon, and insulin-dextrose (similar to beta-blocker overdose). Avoid non-DHP CCBs in patients with systolic heart failure due to negative inotropic effects. Drug interactions: grapefruit juice inhibits CYP3A4 metabolism, increasing CCB levels.
Sources
- Katzung's Basic and Clinical Pharmacology
- First Aid for the USMLE Step 1
- Goodman & Gilman's Pharmacological Basis of Therapeutics
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