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.
Back to Medication Index
Medical Disclaimer
  • For Educational Purposes Only: This content is intended for educational reference and should not be used for clinical decision-making.
  • Not a Substitute for Professional Judgment: Always consult your local protocols, institutional guidelines, and supervising physicians.
  • Verify Before Acting: Users are responsible for verifying information through authoritative sources before any clinical application.
AI Assistance Notice
AI was used to assist in organizing and formatting this information. All content is reviewed for accuracy.