Known brand names include Cardizem.
A calcium channel blocker that slows the heart rate and relaxes blood vessels. Given IV in a monitored setting, it quickly slows a racing heart in atrial fibrillation or flutter and can stop PSVT; as once-daily Cardizem CD capsules, it treats high blood pressure and prevents chest pain (angina).
Labeled use. IV bolus: rapid conversion of PSVT to sinus rhythm after vagal maneuvers.
Sources: [1]
Labeled use. IV: short-term control of a rapid ventricular rate in atrial fibrillation or atrial flutter, not with an accessory pathway.
Sources: [1]
IV diltiazem or a beta blocker is first-line rate control for atrial fibrillation or flutter with a fast ventricular rate; with reduced ejection fraction, a beta blocker or digoxin is preferred, and in decompensated heart failure, digoxin or amiodarone. Unlike amlodipine, diltiazem slows heart rate and AV conduction, which helps with rate control but adds to the effect of beta blockers. For PSVT, adenosine is usually tried first after vagal maneuvers, with diltiazem as an alternative. Never use it for pre-excited atrial fibrillation (WPW) or a wide-complex tachycardia of uncertain origin.
A non-dihydropyridine (benzothiazepine) calcium channel blocker. It inhibits calcium influx into cardiac and vascular smooth muscle during depolarization, which slows AV nodal conduction, prolongs AV nodal refractoriness (most at fast rates), and lengthens the sinus cycle; it has no significant effect on fast sodium channel tissue such as His-Purkinje fibers or accessory pathways. Vascular relaxation lowers peripheral resistance and blood pressure and dilates the coronary arteries, preventing spasm. IV: response within 3 minutes, peak heart rate effect in 2 to 7 minutes, half-life about 3.4 hours. Oral: about 40% bioavailable after extensive first-pass metabolism; it is a CYP3A4 substrate and inhibitor.
The labels do not describe a narrow therapeutic index or direct dosing by measured blood levels of the drug.
Doses come from the FDA label. Study tool, not for clinical decisions.
No labeled dose change. Renal impairment, even end-stage disease, did not appear to alter oral diltiazem disposition, but the labels advise caution in renal impairment and periodic renal function tests, especially in older adults. Dialysis does not remove it.
No labeled dose table. It is extensively metabolized by the liver; in cirrhosis the half-life rose and oral bioavailability increased 69%, so use caution and monitor liver tests. Acute hepatic injury has occurred, usually 1 to 8 weeks after starting, and reversed when the drug was stopped.
Sources: [1]
No specific antidote; give supportive care. Bradycardia or high-degree AV block: atropine (0.6 to 1 mg), then cautious isoproterenol if there is no response; fixed high-degree block needs pacing. Heart failure: inotropes (isoproterenol, dopamine, or dobutamine) and diuretics. Hypotension: vasopressors such as dopamine or norepinephrine. IV calcium (calcium chloride 1 g or calcium gluconate 3 g, each given over 5 minutes, with repeat doses every 10 to 20 minutes as needed) has given inconsistent results but improved the response to atropine in some cases; watch for hypercalcemia. Dialysis does not remove diltiazem.
No well-controlled studies in pregnant women. In animals, doses 5 to 10 times the recommended human dose caused embryo and fetal death and sometimes skeletal abnormalities, and higher doses increased stillbirths. Use in pregnancy only if the potential benefit justifies the risk to the fetus.
Diltiazem passes into breast milk, possibly at levels close to those in the mother's blood. If the drug is essential, the labels advise feeding the infant another way.
Safety and effectiveness in children have not been established for either the IV or the oral form.
In IV atrial fibrillation or flutter trials, 135 of 257 patients were over 65, with no overall difference in safety or response. Start at the low end of the dose range, and consider monitoring renal function, since older adults more often have reduced kidney, liver, or heart function.