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Bedside Snapshot
  • Core dose: IV bolus: 0.25 mg/kg (usual 15–20 mg) over 2 min; if inadequate after 15 min, give 0.35 mg/kg (20–25 mg) over 2 min; then continuous infusion 5–15 mg/h titrated to heart rate and BP
  • Onset/duration: IV onset 2–7 min, peak effect 5–15 min; infusion maintains effect; elimination half-life ~3–5 h
  • Key danger: Hypotension, bradycardia, high-degree AV block; can worsen decompensated HFrEF (negative inotropy); absolutely avoid in WPW with AF (can accelerate ventricular rate); do not combine with IV beta-blockers
  • Special: Non-dihydropyridine CCB; blocks AV node → rate control in AF/AFL/SVT; less negative inotropy than verapamil; CYP3A4 substrate and moderate inhibitor; monitor HR, BP, and rhythm during infusion
Brand & Generic Names
  • Generic Name: Diltiazem hydrochloride
  • Brand Names: Cardizem (IV/PO), Cardizem CD/LA (ER), Cartia XT, Taztia XT, Dilacor XR (ER), and others
Medication Class

Non-dihydropyridine calcium channel blocker (rate-limiting); negative chronotrope/dromotrope with mild-moderate vasodilation.

Pharmacology

Mechanism of Action:

  • Blocks L-type calcium channels in the AV node → slows conduction and increases AV nodal refractoriness → ventricular rate control in AF/AFL and SVT
  • Reduces calcium influx in vascular smooth muscle → vasodilation and lowered blood pressure
  • Negative inotropy (less than verapamil) may worsen decompensated HFrEF

Pharmacokinetics:

  • Onset: IV onset 2–7 min after bolus; peak effect within ~5–15 min; infusion maintains effect
  • Half-life: Elimination half-life ~3–5 h (IV/IR PO); ER products extend apparent half-life
  • Metabolism: High first-pass metabolism; hepatic (CYP3A4 substrate and moderate inhibitor)
  • Distribution: ~80% protein bound
  • Elimination: Biliary/renal elimination of metabolites
Indications
  • Rate control in atrial fibrillation or flutter with rapid ventricular response (hemodynamically stable)
  • Termination or rate control of PSVT/AVNRT/AVRT when adenosine is ineffective/contraindicated and patient is stable
  • Adjunct antihypertensive in selected scenarios (IV/PO) when tachyarrhythmia with hypertension co-exists
Conditions Treated
  • Atrial fibrillation with rapid ventricular response (AF with RVR)
  • Atrial flutter with rapid ventricular response (AFL with RVR)
  • Paroxysmal supraventricular tachycardia (PSVT)
  • AV nodal reentrant tachycardia (AVNRT)
  • AV reentrant tachycardia (AVRT)
  • Hypertension (as adjunct in selected scenarios with tachyarrhythmia)
Dosing & Administration

Available Forms:

  • IV solution for bolus administration
  • IV infusion (premixed bags commonly 100–125 mg in 100–125 mL ≈1 mg/mL)
  • Immediate-release (IR) tablets: 30 mg, 60 mg
  • Extended-release (ER) tablets/capsules: various strengths (120–180 mg and higher)

Standard Adult Dosing (AF/AFL with RVR or PSVT):

Route Initial Dose Repeat/Infusion Notes
IV Bolus (First Dose) 0.25 mg/kg (usual 15–20 mg) IV over 2 min If inadequate after 15 min, give second bolus Weight-based dosing is preferred
IV Bolus (Second Dose) 0.35 mg/kg (usual 20–25 mg) IV over 2 min Give 15 min after first dose if needed May follow with infusion
IV Infusion Start at 5 mg/h Titrate by 2.5 mg/h every 15–30 min Target rate: 5–15 mg/h; maintain target HR (e.g., <110 bpm) while preserving BP
Oral (Transition) IR: 30–60 mg PO every 6 h
ER: 120–180 mg PO daily		 Give first PO dose 1–2 h before stopping infusion Titrate to clinical response and BP

Pediatric Dosing:

  • Generally avoided in infants; limited data in children
  • Some protocols use 0.25 mg/kg IV over 2 min (max 10–20 mg)
  • Consult pediatric cardiology/PALS guidance before use
Administration Note: Use dedicated line when possible. Premixed IV bags are commonly 100–125 mg in 100–125 mL (≈1 mg/mL).
Contraindications

Absolute Contraindications:

  • Severe hypotension
  • Cardiogenic shock
  • Second- or third-degree AV block or sick sinus syndrome without a pacemaker
  • Acute decompensated heart failure with reduced ejection fraction (HFrEF) due to negative inotropy
  • Atrial fibrillation/flutter with preexcitation (WPW or other accessory pathway)—risk of ventricular fibrillation

Precautions:

  • Use caution with concurrent β-blockers (increased risk of bradycardia/heart block)
  • Monitor closely in hepatic impairment
  • Elderly patients may have increased sensitivity to hypotension/bradycardia
Critical Warning: Do NOT use for pre-excited atrial fibrillation (WPW syndrome). If uncertain and the QRS is wide/irregular, avoid AV nodal blockers and seek expert consultation immediately.
Adverse Effects

Common:

  • Hypotension
  • Bradycardia
  • Dizziness
  • Fatigue
  • Peripheral edema
  • Headache
  • Flushing
  • Nausea/constipation (usually milder than with verapamil)

Serious:

  • AV block (second- or third-degree)
  • Severe hypotension
  • Worsening heart failure in HFrEF
  • Elevated liver function tests (LFTs)
  • Rash (rare)
Drug Interactions
  • CYP3A4 Substrate/Moderate Inhibitor: Diltiazem increases levels of cyclosporine, tacrolimus, carbamazepine, and some statins. Limit simvastatin to ≤10 mg/day; consider lower doses of other statins and monitor for myopathy.
  • β-Blockers: Additive AV nodal blockade; increased risk of bradycardia and heart block. Monitor heart rate and PR interval closely.
  • Digoxin: Diltiazem may modestly increase digoxin levels. Monitor digoxin levels and for signs of toxicity.
  • Amiodarone: Additive AV nodal blockade; monitor heart rate and PR interval.
  • Strong CYP3A4 Inducers (e.g., rifampin): May decrease diltiazem levels; avoid unless benefits outweigh risks.
  • Strong CYP3A4 Inhibitors (e.g., clarithromycin): May increase diltiazem levels; avoid unless benefits outweigh risks.
Clinical Pearls
Weight-Based Dosing: Weight-based boluses outperform flat doses. Large patients are often underdosed with a standard "10 mg" push. Always calculate 0.25 mg/kg for the first dose.
Infusion Strategy: Start an infusion soon after an effective bolus to prevent rebound tachycardia. Titrate slowly if blood pressure is marginal to avoid hypotension.
Decompensated HFrEF: In decompensated heart failure with reduced ejection fraction or borderline perfusion, prefer amiodarone or digoxin for rate control. Consider early cardioversion if the patient becomes unstable.
Pre-Excited Atrial Fibrillation: Do NOT use diltiazem for pre-excited AF (WPW syndrome). If uncertain and the QRS is wide/irregular, avoid AV nodal blockers and seek expert input immediately.
Transitioning to Oral: When converting to oral therapy, overlap by 1–2 hours to avoid rebound tachycardia. Reassess heart rate after each dose change and monitor blood pressure closely.
Managing Hypotension: If hypotension occurs during IV dosing, pause or slow the infusion, administer IV fluids or vasopressor support as indicated, and consider switching to an alternative agent.
Target Heart Rate: Aim for a target ventricular rate (e.g., <110 bpm at rest) while preserving blood pressure and perfusion. Avoid over-aggressive rate control that compromises hemodynamics.
References
  • 1. Papadopoulos, J. (2008). Pocket guide to critical care pharmacotherapy. Humana Press.
  • 2. Medscape. (n.d.). Diltiazem (Cardizem): Drug monograph & dosing. Retrieved 2025-11-12, from https://reference.medscape.com
  • 3. DrugBank Online. (n.d.). Diltiazem (DB00343). Retrieved 2025-11-12, from https://go.drugbank.com/drugs/DB00343
  • 4. Boucher, B. A., Wood, G. C., & Swanson, J. M. (2006). Pharmacokinetic changes in critical illness. Critical Care Clinics, 22(2), 255–271.
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