Diltiazem (Cardizem)

Emergency & Prehospital

• Atrial fibrillation (AF) or atrial flutter with rapid ventricular response (RVR): hemodynamically stable, no pre-excitation, left ventricular ejection fraction (LVEF) >40%; FDA-labeled for temporary rate control and an ACC/AHA first-line option with beta-blockers
• Stable paroxysmal supraventricular tachycardia (PSVT): AV nodal re-entry or orthodromic AV re-entry (narrow, regular); FDA-labeled for rapid conversion to sinus rhythm after vagal maneuvers; AHA guidance places it after adenosine (or when adenosine fails, recurs or is unsuitable)

ED / ICU / Transport

• Ongoing AF/flutter rate control: continuous infusion for up to 24 hr after an effective bolus, then oral or other agents

Other Uses

• Long-term AF rate control (oral): LVEF >40%
• Chronic stable angina and coronary vasospasm (oral): FDA-labeled
• Hypertension (oral extended-release): FDA-labeled for extended-release products

These doses follow the FDA label and AHA 2025. Your protocol may differ from them.

Available Forms

• Injection (bolus or infusion): 5 mg/mL in 5 mL (25 mg), 10 mL (50 mg) and 25 mL (125 mg) single-dose vials; the vial EMS and transport usually carry. Refrigerated.
• Premixed bag (1 mg/mL): 100 mg/100 mL and 250 mg/250 mL in sodium chloride, ready to hang. Labeled for both bolus and infusion, but mainly used for infusion. The bolus is usually drawn from the 5 mg/mL vial (per institution).
• For injection (infusion only): 100 mg lyophilized ADD-Vantage vial, labeled "Not for bolus".
• Oral: immediate-release (IR) tablets 30, 60, 90 and 120 mg (Cardizem tablets); extended-release (ER) once-daily tablets 120, 180, 240, 300, 360 and 420 mg (Cardizem LA); ER capsules are also marketed (Hospira label).

Adult Dosing

Pediatric Dosing

Continuous Infusion

Preparation & Administration

• Bolus: undiluted 5 mg/mL over 2 min (20 mg = 4 mL; 25 mg = 5 mL); flush.
• Infusion dilution (label): 125 mg (25 mL) into 100 mL normal saline, D5W or D5W/0.45% NaCl = 125 mL at 1 mg/mL. Larger bags: 250 mg (50 mL) into 250 mL = 0.83 mg/mL; into 500 mL = 0.45 mg/mL. Keep this vial admixture refrigerated until use (an ADD-Vantage admixture may be kept at room temperature or refrigerated); use within 24 hr.
• Line: dedicated line when possible; do not mix with other drugs in the same container.
• Pump: infusion on a smart pump in mg/hr; start it right after the effective bolus.
• Transition: move to an oral or other agent within 24 hr. The effect can last a median of 7 hr after the infusion stops. Reassess before you stack a new AV-nodal blocker on top.

For renal and hepatic dosing, see Special Populations.

Contraindications

• Sick sinus syndrome or 2nd/3rd-degree AV block without a functioning ventricular pacemaker
• Severe hypotension or cardiogenic shock
• AF or atrial flutter with an accessory pathway (Wolff-Parkinson-White, WPW, or short-PR syndrome)
• Ventricular tachycardia, or a wide-complex tachycardia (QRS ≥0.12 s) not proven supraventricular
• IV beta-blocker given together or within a few hours
• Moderate or severe LV systolic dysfunction, decompensated or not (ACC/AHA 3: Harm for IV use); acute decompensated heart failure or cardiogenic shock (label: do not initiate)
• Oral diltiazem: acute myocardial infarction with pulmonary congestion on chest x-ray
• Hypersensitivity to diltiazem

Precautions

• Borderline blood pressure or volume depletion: Hypotension is the main adverse effect. Correct volume first, or choose another agent.
• Drugs that lower BP, contractility or conduction: Effects add up. A patient on an oral beta-blocker can still get IV diltiazem, with close monitoring.
• Acute coronary syndrome or acute MI: Avoid IV diltiazem (AHA 2025 rate-control table), especially with pulmonary congestion or LV dysfunction. In ACS, AF with ongoing ischemia, hemodynamic compromise or poor rate control needs urgent synchronized cardioversion.
• Older adults, hepatic or renal impairment: start at the low end of the range.
• AF over 48 hr or unknown onset: Diltiazem rarely converts AF. Any conversion carries stroke risk, so address anticoagulation before a planned cardioversion.

Hold / Reassess If

• SBP <90 mmHg or symptomatic hypotension: stop the bolus or infusion; fluids; see Reversal
• Symptomatic bradycardia, pauses, junctional rhythm or new 2nd/3rd-degree AV block: stop; atropine or pacing ready
• New crackles, rising O₂ need or falling perfusion: stop; treat heart failure
• QRS widens or the rhythm turns irregular and broad: stop; reassess for pre-excitation or VT

Common

• Hypotension: asymptomatic 4.3%, symptomatic 3.2% in IV trials; usually fluids or positioning were enough
• Injection-site itching or burning: 3.9%
• Flushing: 1.7%
• Junctional rhythm or isorhythmic dissociation: 1%
• Transient ventricular premature beats on conversion of PSVT (benign)
• Oral: edema, headache, dizziness, constipation, nausea

Serious / Life-Threatening

Overdose & Toxicity Management

• Signs: Expect hypotension, bradycardia, AV block, cardiogenic or vasoplegic shock. Toxicity can be delayed, especially after an extended-release ingestion.
• Ingestion, still well: Send every intentional ingestion to the ED, and any ingestion above the usual maximum single dose. Toxicity can show up late. An asymptomatic patient is unlikely to develop symptoms more than 6 hr after an IR ingestion, or more than 18 hr after a modified-release diltiazem ingestion. Follow poison center advice on observation, which is often longer for ER products. Consider activated charcoal if it is available and there is no contraindication. Do not delay transport for it (see the CCB consensus guideline in References).
• Treat (2025 AHA Guidelines, Part 10): crystalloid boluses while the patient is fluid-responsive; norepinephrine and/or epinephrine for hypotension (vasopressors, Class 1, C-LD; high-dose insulin for hypotension is also Class 1, B-NR); high-dose insulin 1 unit/kg IV, then 1–10 units/kg/hr with dextrose and potassium monitoring (Table 4); IV calcium chloride 2 g (20 mL of 10%), or calcium gluconate 6 g if peripheral (Class 2a, C-EO), then 20–40 mg/kg/hr of calcium chloride titrated to BP, without exceeding an ionized calcium of 1.5–2 times the upper limit of normal; methylene blue for refractory vasodilatory shock (Class 2b, C-EO): 1–2 mg/kg IV, repeated hourly if needed, then 1 mg/kg/hr, maximum 5–7 mg/kg; glucagon (Class 2b, C-EO); atropine for symptomatic bradycardia is standard ALS, not a Part 10 recommendation.
• Pediatric calcium: calcium chloride 20 mg/kg (0.2 mL/kg of 10%) IV slowly over 10 min, max 1 g or 10 mL per dose (NASEMSO v3.0 p. 296, calcium channel blocker poisoning). Calcium gluconate 60 mg/kg over 10 min is preferred in children because chloride carries more tissue-injury risk (NASEMSO v3.0 p. 296). Differs: AHA 2025 Part 10 Table 4 gives 20 mg/kg with no child maximum (adult ceiling 2 g). Central line preferred in children; see the calcium chloride page.
• Refractory: Escalate insulin. Use transcutaneous pacing for unstable bradycardia. VA-ECMO is for refractory cardiogenic shock or cardiac arrest (Class 2a: adults B-NR, children C-LD). IV lipid emulsion has uncertain usefulness (Class 2b, C-EO). An expert consensus advises against routine use, so give it only on toxicology advice.
• Removal: Hemodialysis and peritoneal dialysis do not remove it. Call poison control (1-800-222-1222).

Clinically Significant Interactions

IV Compatibility

• Diluents: normal saline, D5W, D5W/0.45% NaCl (stable 24 hr at up to 1 mg/mL).
• Same container: do not mix with other drugs; use a dedicated line when possible.
• Y-site incompatible (label): acetazolamide, acyclovir, aminophylline, ampicillin ± sulbactam, cefoperazone, diazepam, furosemide, hydrocortisone and methylprednisolone sodium succinate, regular insulin, nafcillin, phenytoin, rifampin, sodium bicarbonate. Several were compatible with the 1 mg/mL ADD-Vantage product only; treat all as incompatible.
• Verify with an institutional compatibility resource.

• Pediatrics: Safety and effectiveness are not established, so this is specialist use only. Avoid it in infants, where the risk is profound hypotension and cardiovascular collapse. The Pediatric Dosing block has the alternative pathway.
• Pregnancy: Decades of published use have not identified a drug-associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. Animal studies at 5–10 times human doses did show embryo-fetal harm. ACC/AHA prefer beta-blockers or digoxin for rate control in pregnancy. Electrical cardioversion is safe. In an emergency, treat the mother.
• Lactation: It gets into breast milk at levels that may approach serum, and effects on the infant are unknown. The labels do not agree. The premixed-bag label says to weigh breastfeeding benefits against the mother's need. The vial label says to use another feeding method if diltiazem is essential.
• Older Adults: Start at the low end of the range. The AGS Beers Criteria 2023 says to avoid nondihydropyridine CCBs in heart failure with reduced ejection fraction (HFrEF). See Heart Failure below.
• Renal Impairment: No specific adjustment is established. In label studies, renal failure did not change oral disposition. Dialysis does not remove it.
• Hepatic Impairment: Cirrhosis cut oral clearance and stretched the half-life. Use with caution and titrate carefully.
• Obesity / Dosing Weight: The label bases the bolus on actual body weight. Obesity dosing is not well studied, so follow local protocol for any per-dose cap.
• Heart Failure: IV diltiazem is an option when LVEF >40% and the patient is not in acute decompensated HF. Do not give it with known moderate or severe LV systolic dysfunction, decompensated or not (ACC/AHA 3: Harm). Do not give it in acute decompensated HF or cardiogenic shock either (label).

• Scope: usually paramedic and critical-care transport, per local protocol; varies by state and agency protocol.
• Storage & Stability: Keep vials and premixed bags refrigerated at 2–8°C (36–46°F). Do not freeze them. Either can sit at room temperature for up to 1 month, then discard it. Date the box the moment it leaves the refrigerator. For premixed bags, that month counts only in the original aluminum overwrap. Out of the overwrap, use within 28 days. Lyophilized vials live at room temperature.
• Carried Concentration: Carry 5 mg/mL vials for boluses. Infusions run at 1 mg/mL. Never draw a bolus from the lyophilized ADD-Vantage vial (infusion only).
• Infusions in Transport: smart pump in mg/hr, dedicated line, enough volume for the trip; confirm the concentration and the 24-hr start time at handoff.
• Handoff Essentials: each bolus time, dose in mg and mg/kg, infusion rate and start time, HR and BP response, any hypotension treatment, AF onset time, anticoagulant use and known LVEF.

Mechanism of Action

• L-type Ca²⁺ channel block in the AV node: Conduction slows and refractoriness lengthens. That gives ventricular rate control in AF/flutter and ends AV-nodal re-entry.
• Use-dependent: The effect is stronger at fast rates. At normal rates it does little to normal AV conduction.
• No effect on accessory pathways or His-Purkinje tissue: That is why it cannot slow pre-excited AF, and why it may speed it up.
• Vascular smooth muscle: Systemic vascular resistance drops, so BP falls. Negative inotropy can worsen systolic function.

Pharmacokinetics

• Half-life: about 3.4 hr after an IV bolus; 4–5 hr during infusion (nonlinear kinetics); 3–4.5 hr orally.
• Metabolism: extensive hepatic (CYP3A4 substrate and inhibitor); oral bioavailability about 40% after first-pass metabolism.
• Active metabolites: desacetyldiltiazem (25–50% as potent as a coronary vasodilator), seen after oral use or a 24-hr infusion.
• Elimination: metabolites in urine and bile; 2–4% unchanged in urine; not dialyzable.
• Protein binding / Vd: 70–80%; about 305 L.

Generic Name

Diltiazem hydrochloride

Brand Names

Cardizem (IR tablets), Cardizem CD, Cardizem LA, Cartia XT, Tiazac, Matzim LA; injection sold as generic

Pharmacologic Class

Nondihydropyridine (benzothiazepine) calcium channel blocker; Vaughan Williams class IV

Therapeutic Class

Antiarrhythmic (AV-nodal rate control); antianginal; antihypertensive

Controlled Substance

Not controlled

ISMP High-Alert

Yes: ISMP high-alert medication (antiarrhythmics, IV); diltiazem is not a named example

Look-Alike / Sound-Alike

Product mix-up: diltiazem injection (bolus or infusion) vs diltiazem for injection (infusion only, not for bolus)