Calcium channel blocker · Antiarrhythmic · Rate control
Diltiazem (Cardizem)
Also called Cardizem
Indications
- Temporary rate control in atrial fibrillation or flutter
- Conversion of PSVT, usually after vagal maneuvers and adenosine
- Rate control in multifocal atrial tachycardia (off-label)
- Rate control when beta-blockers are contraindicated, as in aortic dissection (off-label)
- Oral forms: hypertension, chronic stable angina and coronary vasospasm
Dosing
Diltiazem drip card and mL/h converterStart: 0.25 mg/kg over 2 minutes, then 5–10 mg/h
| Where | Dose |
|---|---|
| Rhythm control | Diltiazem: 0.25 mg/kg (about 15–20 mg) over 2 min; repeat 0.35 mg/kg after 15 min; then 5–15 mg/h |
On the quick cards
Mechanism of action
Diltiazem is a benzothiazepine, a non-dihydropyridine L-type (Cav1.2) calcium channel blocker. It binds in the central cavity of the α1C pore, and its binding is use-dependent, so block builds with each beat and is strongest in fast-firing nodal tissue. Because the SA and AV nodes depolarize by L-type calcium current, it slows the sinus rate and AV conduction and lengthens nodal refractoriness; it also relaxes arterioles and mildly depresses contractility, sitting between verapamil and the vessel-selective dihydropyridines.
Pharmacology
- Cardiovascular: slows AV conduction and the ventricular rate in AF; the effect grows with heart rate and is small at normal rates
- Cardiovascular: modest sinus slowing and PR prolongation
- Cardiovascular: lowers BP and SVR and raises coronary flow, with less reflex tachycardia than dihydropyridines
- Cardiovascular: mild negative inotropy that can worsen low-EF heart failure
Pharmacokinetics
| Onset | IV bolus: rate response within 3 min, maximal at 2–7 min |
|---|---|
| Duration | 1–3 h after a bolus; median 7 h (0.5 to over 10) after an infusion |
| Half-life | 3.4 h after one IV dose; 4.1–4.9 h during infusions |
| Distribution | Vd about 305 L (roughly 4 L/kg) |
| Protein binding | 70–80% |
| Metabolism | Hepatic deacetylation and CYP3A4 demethylation (desacetyldiltiazem keeps 25–50% of the coronary effect); inhibits CYP3A4 and P-glycoprotein |
| Clearance | About 65 L/h; lower at high infusion rates (nonlinear) and in AF |
| Elimination | Metabolites in urine and bile; 2–4% unchanged in urine |
| Organ failure | Cirrhosis lowers clearance and prolongs the half-life |
| Bioavailability | About 40% orally after first-pass metabolism |
Chemistry
- A 1,5-benzothiazepin-4-one with a 4-methoxyphenyl ring, an acetate ester and a dimethylaminoethyl side chain
- A single stereoisomer, the (+)-cis (2S,3S) form, not a racemate
- pKa about 8.0 (tertiary amine): about 80% ionized at pH 7.4; the hydrochloride is water soluble
- Injection 5 mg/mL, pH 3.7–4.1; refrigerate (up to 1 month at room temperature)
- Precipitates with furosemide, phenytoin, diazepam, sodium bicarbonate and others: use its own line
Adverse effects and cautions
In the one-pagers
- Rhythm GallerySinus, atrial and junctional: Atrial fibrillation: irregularly irregular, no P waves, wavy baseline. Stable: IV beta-blocker, or diltiazem only if EF is over 40%. Unstable: synchronized cardioversion.
- ACLS Algorithms in BriefTachycardia with a pulse: Then a beta-blocker or calcium channel blocker (not diltiazem or verapamil in suspected systolic heart failure)
- After Cardiac SurgeryPost-op atrial fibrillation: Unstable POAF gets synchronized cardioversion (STS 2026 Class I). In stable patients, rate control (beta-blocker or diltiazem, amiodarone if pressure or EF is low) and rhythm control (amiodarone, then cardioversion) gave equal hospital days, and most patients were in sinus rhythm by 60 days (CTSN 2016). Replace K and Mg. Anticoagulation waits until bleeding risk settle
- Aortic Dissection and Hypertensive EmergencyAnti-impulse therapy in depth: An IV beta-blocker comes first (Class 1). A vasodilator alone triggers reflex tachycardia and a steeper upstroke, so it is added only if BP stays high after rate control (Class 1): nicardipine or clevidipine, or nitroprusside, which is fastest but releases cyanide above about 2 mcg/kg/min (label). Esmolol (half-life about 9 min) wears off in minutes if it is not tole
- Endocarditis and Valve EmergenciesObstructive emergencies and LVOT obstruction: Obstructive HCM therapies with ICU consequences. Mavacamten, a cardiac myosin inhibitor, lowers contractility; it is interrupted if LVEF falls below 50%, its label says to avoid disopyramide, ranolazine, and verapamil or diltiazem with a beta-blocker, to consider interruption during intercurrent illness, and to delay dose increases with arrhythmia such
- Heart FailureDecompensated HF in the ICU: the first hours: Find the trigger: nonadherence, ACS, arrhythmia, uncontrolled hypertension, infection, PE, thyroid disease, NSAIDs, nondihydropyridine calcium channel blockers or thiazolidinediones. For AF with rapid ventricular response in decompensated HFrEF, use amiodarone or digoxin, a cautious β-blocker if perfusion allows, or cardioversion if unstable; diltiazem
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Sources
- FDA label: diltiazem HCl injection, Hospira (2026)
- FDA label: Cardizem (2025)
- 2023 ACC/AHA/ACCP/HRS AF guideline
- PubChem: diltiazem
For education and exam preparation only. Follow your institution’s protocols. Typical adult values for study. Follow the order, the label and your institution's protocols.