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
Infusion start: 0.25 mg/kg over 2 minutes, then 5–10 mg/h. Titration: 5 mg/h steps.
| 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.
- 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
- Pharmacology by Class and SuffixHeart and blood pressure: the why behind the checks: -dipine. Dihydropyridine calcium channel blockers dilate arterioles: headache, flushing, palpitations and dose-related ankle edema (about 11% at amlodipine 10 mg against under 1% on placebo, amlodipine label). Verapamil (-pamil) and diltiazem act mainly on the heart and are held for bradycardia. Grapefruit raises some calcium channel blocker lev
- Toxidromes and AntidotesCardiotoxic drugs: TCAs, β-blockers, CCBs, digoxin, LAST: β-blockers lower cAMP: bradycardia, AV block, poor contractility and, mainly in children, hypoglycemia; propranolol also blocks sodium channels and sotalol prolongs QT. Verapamil and diltiazem slow the heart and depress output; dihydropyridines dilate arterioles with reflex tachycardia until large doses erase the difference. CCBs block insu
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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.