diltiazem
Summary
Diltiazem is a non-dihydropyridine calcium channel blocker (CCB) used for hypertension, angina, and rate control in atrial fibrillation/flutter. It works by blocking L-type calcium channels in cardiac and vascular smooth muscle, causing both negative chronotropic/inotropic effects and vasodilation.
Detail
Diltiazem belongs to the benzothiazepine class of calcium channel blockers, along with verapamil (phenylalkylamine), classified as non-dihydropyridine CCBs. Unlike dihydropyridines (e.g., amlodipine, nifedipine), which act primarily on vascular smooth muscle, diltiazem has significant effects on both the heart and vasculature.
Mechanism: Diltiazem blocks voltage-gated L-type calcium channels, inhibiting calcium influx into cardiac myocytes and vascular smooth muscle cells. In the heart, this decreases SA node automaticity (negative chronotropy), slows AV node conduction (used to treat SVT and control ventricular rate in AF/flutter), and reduces myocardial contractility (negative inotropy). In vascular smooth muscle, it causes vasodilation, reducing systemic vascular resistance and afterload, which helps in hypertension and angina by decreasing myocardial oxygen demand.
Clinical uses: Hypertension, chronic stable angina, Prinzmetal (vasospastic) angina, rate control in atrial fibrillation/flutter, and some supraventricular tachycardias. It is often preferred over beta-blockers in patients with reactive airway disease since it doesn't cause bronchoconstriction.
Adverse effects: Bradycardia, AV block, hypotension, peripheral edema, constipation, and negative inotropic effects that can worsen heart failure with reduced ejection fraction (contraindicated in decompensated HF, severe LV dysfunction). Caution when combined with beta-blockers or digoxin due to additive AV nodal blockade and risk of severe bradycardia/heart block.
Contraindications: Sick sinus syndrome, 2nd/3rd degree AV block (without pacemaker), severe hypotension, decompensated heart failure with reduced EF.
Metabolism: Hepatic via CYP3A4; it is also a moderate CYP3A4 inhibitor, so can increase levels of other CYP3A4 substrates (e.g., statins, cyclosporine).
High-yield board point: Diltiazem and verapamil are grouped for their combined cardiac and vascular effects, contrasted with dihydropyridines which are more vasoselective and lack significant AV nodal blocking effects.
Sources
- Katzung's Basic and Clinical Pharmacology
- First Aid for the USMLE Step 1
- Goodman & Gilman's The Pharmacological Basis of Therapeutics
- UpToDate: Calcium channel blockers in the treatment of hypertension and arrhythmias
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