Diltiazem
Diltiazem Hydrochloride
Also known as: Cardizem CD · Cardizem LA · Dilacor XR · Cartia XT · Tiazac · Diltia XT · Taztia XT · Dilt-CD · Hypercard · Adizem · Angitil · Dilcardia · Dilzem · Slozem · Tildiem · Viazem · Zemret · CRD-401 · diltiazemi hydrochloridum · latiazem hydrochloride · MK-793 · Diltiazem hydrochloride
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Decreasing ventricular rate in dogs with atrial fibrillation | Initially, 0.5 mg/kg PO q8h, if response not adequate can increase to 1 mg/kg PO q8h and finally, to 1.5 mg/kg PO q8h. | PO | q8h | — | 🌎 NA |
| Acute treatment of supraventricular tachycardia | 0.05 mg/kg IV administered over 1-2 minutes. May repeat this dose up to two times, with 5 minutes between doses. Some cardiologists use a dose of 0.25 mg/kg administered over 5 minutes. | IV | As directed | — | 🌎 NA |
| Chronic treatment of supraventricular tachycardia | Initially, 1 mg/kg PO q8h and titrated upward to a maximum of 4 mg/kg PO q8h. | PO | q8h | — | 🌎 NA |
| Acute treatment of atrial tachycardia | 0.05-0.15 mg/kg slowly IV, repeat every 5 minutes to effect or until a total dose of 0.1-0.3 mg/kg; OR give 0.5 mg/kg PO followed by 0.25 mg/kg PO every hour until conversion or a total oral dose of 1.5-2 mg/kg has been given. | IV/PO | As directed | — | 🌎 NA |
| Chronic treatment of atrial tachycardia | May give an initial dose of 0.5 mg/kg PO q8h up to 2 mg/kg. | PO | q8h | — | 🌎 NA |
| Emergency treatment of supraventricular tachyarrhythmias | Initially, 0.25 mg/kg IV bolus given over 2 minutes; subsequent 0.25 mg/kg boluses may be repeated at 15 minute intervals until conversion occurs or to a maximum (total) dose of 0.75 mg/kg. | IV | q15min | — | 🌎 NA |
| Adjunctive treatment of pulmonary hypertension | 1-2 mg/kg PO three times daily. | PO | TID | — | 🌎 NA |
| Emergency management of hypertension (when nitroprusside unavailable) | 0.5 mg/kg PO q6h | PO | q6h | — | 🌎 NA |
| Supraventricular tachyarrhythmias / Atrial fibrillation | 0.05-0.25 mg/kg | IV | single dose over 1-2 min | — | 🌍 EU |
| Supraventricular tachyarrhythmias / Atrial fibrillation | 0.5-2.0 mg/kg | PO | q8h | — | 🌍 EU |
| Supraventricular tachyarrhythmias / Atrial fibrillation | up to 3.0 mg/kg | PO | q12h | — | 🌍 EU |
| Supraventricular tachyarrhythmias / Atrial fibrillation | 10 mg/kg | PO | q24h | — | 🌍 EU |
| Refractory supraventricular tachyarrhythmias | up to 4 mg/kg | PO | q8h | — | 🌍 EU |
- Decreasing ventricular rate in dogs with atrial fibrillation: Digoxin most commonly used first. In general, do not use with beta blocker.
- Chronic treatment of supraventricular tachycardia: Doses from 2-4 mg/kg q8h should probably not be given to dogs that have moderate to severe myocardial failure or with significant cardiac compromise.
- Emergency management of hypertension (when nitroprusside unavailable): If blood pressure not controlled, may add a betablocker (e.g., atenolol).
- Supraventricular tachyarrhythmias / Atrial fibrillation: Lower doses are preferred in the presence of heart failure.
- Supraventricular tachyarrhythmias / Atrial fibrillation: For modified-release (-MR) products.
- Supraventricular tachyarrhythmias / Atrial fibrillation: For sustained/extended release (-SR) preparations (little evidence established).
- Supraventricular tachyarrhythmias / Atrial fibrillation: For long-acting preparations; little experience with such formulations in animals.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Treatment of hypertrophic cardiomyopathy (Option A) | 7.5 mg (total dose) PO q8-12h; Long-acting forms: Cardizem CD Capsules: 10 mg/kg once daily. Dilacor XR Capsules: 15-30 mg total dose q12-24h. | PO | q8-24h | — | 🌎 NA |
| Treatment of hypertrophic cardiomyopathy (Option B) | 1.75-2.5 mg/kg PO q8h or sustained release (Dilacor) dosed at 30 mg (total dose) PO q12h | PO | q8-12h | — | 🌎 NA |
| Treatment of hypertrophic cardiomyopathy (Option C) | 7.5-15 mg (total dose) per cat PO q8h. Alternatively, the sustainedrelease products Cardizem CD at 45 mg (total dose) PO q24h or Dilacor XR at 30 mg (total dose; 1/2 of one of the 60 mg tablets found within the capsule) PO q12h can be used. | PO | q8-24h | — | 🌎 NA |
| Treatment of hypertrophic cardiomyopathy (Option D) | If using standard release formulations: 1-2.5 mg/kg PO q8h; if using sustained release formations: 30-60 mg (total dose per cat) q24h. | PO | q8-24h | — | 🌎 NA |
| Treatment of hypertrophic cardiomyopathy (Option E) | Dilacor XR 30 mg/cat PO q24h. | PO | q24h | — | 🌎 NA |
| Emergency treatment of supraventricular tachyarrhythmias | Initially, 0.25 mg/kg IV bolus given over 2 minutes; subsequent 0.25 mg/kg boluses may be repeated at 15 minute intervals until conversion occurs or to a maximum (total) dose of 0.75 mg/kg. | IV | q15min | — | 🌎 NA |
| Acute management of supraventricular tachyarrhythmias | 0.125-0.35 mg/kg IV | IV | As directed | — | 🌎 NA |
| Chronic management of supraventricular tachyarrhythmias | 7.5 mg (per cat) PO q8h | PO | q8h | — | 🌎 NA |
| Emergency management of hypertension (when nitroprusside unavailable) | 0.5 mg/kg PO q6h | PO | q6h | — | 🌎 NA |
| Supraventricular tachyarrhythmias / Hypertrophic cardiomyopathy | 0.05-0.25 mg/kg | IV | single dose over 1-2 min | — | 🌍 EU |
| Supraventricular tachyarrhythmias / Hypertrophic cardiomyopathy | 0.5-2.5 mg/kg | PO | q8h | — | 🌍 EU |
- Treatment of hypertrophic cardiomyopathy (Option A): Some cats tolerate 60 mg daily, but vomiting may be a problem.
- Treatment of hypertrophic cardiomyopathy (Option D): Also indicated for supraventricular arrhythmias.
- Treatment of hypertrophic cardiomyopathy (Option E): If cat has minimal tachycardia and a loud S4 gallop, many prefer using diltiazem (over a beta blocker).
- Chronic management of supraventricular tachyarrhythmias: Used in combination with digoxin for patients with CHF unless cat has hypertrophic cardiomyopathy and atrial fib, then digoxin not used.
- Emergency management of hypertension (when nitroprusside unavailable): If blood pressure not controlled, may add a betablocker (e.g., atenolol).
- Supraventricular tachyarrhythmias / Hypertrophic cardiomyopathy: Alternatively, one 10 mg tablet for cats of 3-6.25 kg PO q8h.
Ferrets
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Hypertrophic cardiomyopathy | 2-7.5 mg/kg PO twice daily; adjust as necessary. | PO | BID | — | 🌎 NA |
- Hypertrophic cardiomyopathy: May result in heart block.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Diltiazem is a non-dihydropyridine calcium channel blocker and Class IV antiarrhythmic agent used primarily in veterinary medicine to manage supraventricular tachycardias (SVTs), systemic hypertension, pulmonary hypertension, and hypertrophic cardiomyopathy (HCM), particularly in cats.
- Cardiovascular Effects: It acts primarily by slowing conduction through the AV node and promoting vasodilation, making it highly effective for rate control in atrial fibrillation.
- Clinical Utility: While historically a cornerstone for feline HCM, its use for this specific indication has decreased in recent years in favor of other therapies, though it remains a vital tool for tachyarrhythmias.
- Clinical Pearl: Unlike dihydropyridines (e.g., amlodipine) which are potent peripheral vasodilators, diltiazem has more pronounced effects on cardiac conduction, making it superior for rhythm control but less potent for severe systemic hypertension.
Mechanism of action
Diltiazem exerts its effects by binding to the alpha-1 subunit of L-type voltage-gated calcium channels.
- Mechanism: Inhibits transmembrane influx of extracellular calcium ions → decreases intracellular calcium in myocardial cells and vascular smooth muscle.
- Cardiac Conduction: Slows AV node conduction and prolongs refractory times (negative dromotropic effect). It rarely affects SA node conduction except in sick sinus syndrome.
- Vasodilation: Relaxes vascular smooth muscle → dilates main systemic and coronary arteries → reduces total peripheral resistance, blood pressure, and cardiac afterload.
- Inotropy: Can cause mild negative inotropic effects, though rarely of clinical significance compared to verapamil.
Safety & warnings
Contraindications
- Severe hypotension (<90 mm Hg systolic)
- Sick sinus syndrome (unless functioning pacemaker is in place)
- 2nd or 3rd degree AV block (unless functioning pacemaker is in place)
- Acute myocardial infarction
- Radiographically documented pulmonary congestion
- Hypersensitivity to diltiazem
- Second or third degree AV block
- Marked hypotension
- Acute or decompensated congestive heart failure (relative contraindication)
Adverse effects
- Dogs: Bradycardia (most prominent)
- Cats: Vomiting (especially with 60 mg sustained-release pellets)
- Lethargy
- Anorexia / GI distress
- Hypotension
- Heart block or rhythm disturbances
- CNS effects
- Skin rashes
- Elevations in liver enzymes
- Bradycardia (most common in dogs)
- Vomiting (most common in cats)
- AV block
Precautions
Warning: Use with extreme caution in geriatric patients, those with heart failure (especially if receiving beta-blockers), or patients with hepatic or renal impairment.
- IV Administration: If giving direct IV push, administer slowly over at least two minutes to prevent acute hypotension or collapse.
- Pregnancy: Potential teratogen at high doses (FDA Category C). Use only when benefits outweigh risks.
- Nursing: Excreted in milk at concentrations approximating serum levels; use with caution.
Drug interactions
May increase cardiac depressant effects of diltiazem.
Diltiazem may increase benzodiazepine levels.
May increase the likelihood of bradycardia, AV block, or CHF. Diltiazem may substantially increase the bioavailability of propranolol.
Diltiazem may increase buspirone levels.
Could potentially increase risk for increased QT intervals.
Data conflicts regarding pharmacokinetic effects; diligent monitoring of digoxin serum concentrations is required.
May increase plasma diltiazem concentrations; increased monitoring warranted.
May affect diltiazem concentrations, but to a lesser extent than cimetidine.
Diltiazem may increase cyclosporine serum concentrations; monitoring and dosage adjustments may be required.
May decrease diltiazem levels.
Diltiazem may increase quinidine serum concentrations; monitoring and dosage adjustments may be required.
Additive negative inotropic and chronotropic effects. Co-administration is not recommended.
May adversely affect the activity of diltiazem.
May adversely affect the activity of diltiazem.
Diltiazem enhances the effect of theophylline, which may lead to toxicity.
Diltiazem may affect ciclosporin concentrations.
Diltiazem may displace these agents from plasma proteins.
Diltiazem may increase intracellular vincristine levels by inhibiting outflow of the drug from the cell.
Monitoring
- ECG / Heart rate
- Blood pressure
- Adverse effects (vomiting, lethargy)
- Heart rate and rhythm (ECG)
- Renal and hepatic function (periodically)
- Serum digoxin levels (if used concurrently)
Pharmacokinetics
Half-life
Absorption
In humans, ~80% absorbed orally but high first-pass effect limits systemic bioavailability to ~50%. In cats, bioavailability is 50-80% (peak at 45 mins); sustained-release products vary (Cardizem CD 22-59%, Dilacor XR ~94%). In dogs, bioavailability is low (~25%).
Distribution
Approximately 70-75% bound to serum proteins. Enters milk in concentrations approximating plasma levels.
Metabolism
Rapidly and almost completely metabolized in the liver to several metabolites, including two active ones.
Elimination
Renal impairment may slightly increase half-lives.
Overdose
The oral LD50 in dogs is >50 mg/kg.
- Clinical Signs: GI signs, heart block, severe bradycardia, hypotension, CNS depression, and heart failure.
- Treatment:
- Gut emptying protocols if recent ingestion.
- Bradycardia/AV Block: Atropine. If unresponsive to vagal blockade, cautious use of isoproterenol. Fixed block may require temporary transvenous cardiac pacing.
- Hypotension/Heart Failure: Inotropics (dobutamine, dopamine, isoproterenol) and pressors (norepinephrine).
- Antidote: A slow intravenous calcium infusion (1 mL/10 kg body weight of 10% calcium gluconate) may be useful for severe acute toxicity.
Available products
Formulations
- Oral Tablets
- Oral Extended/Sustained Release Capsules and Tablets
- Injection (solution and powder for reconstitution)
- 10 mg modified-release (-MR) tablets
- 60 mg modified-release (-MR) tablets
- 60 mg, 90 mg, 120 mg sustained-release (-SR) capsules
- 10 mg/ml injectable solution
Veterinary
- Hypercard 10 mg modified-release tablets
Human-labeled
- Diltiazem Oral Tablets: 30 mg, 60 mg, 90 mg, & 120 mg (Cardizem, generic)
- Diltiazem Extended/Sustained Release Capsules & Tablets: 60 mg, 90 mg, 120 mg, 180 mg, 240 mg, 300 mg, 360 mg, 420 mg (Cardizem CD & LA, Cartia XT, Dilacor XR, Tiazac, Diltia XT, Taztia XT, Dilt-CD & XR, generic)
- Diltiazem Injection: 5 mg/mL in 5 mL, 10 mL, 25 mL vials
- Diltiazem Powder for Injection: 25 mg in single-use containers
- Adizem
- Angitil
- Dilcardia SR (60 mg, 90 mg, 120 mg capsules)
- Diltiazem generic
- Dilzem
- Slozem
- Tildiem
- Viazem
- Zemret
Regulatory status
POM-V, POM. Hypercard is authorized for veterinary use.
POM-V, POM.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Oral products should be stored at room temperature in tight, light-resistant containers. Powder for injection should be stored between 15-30°C; discard after 24 hours once reconstituted.
Client information
Diltiazem is a medication used to treat abnormal heart rhythms and high blood pressure in pets.
- Administration: Give exactly as prescribed. Do not crush or chew sustained-release capsules unless specifically instructed by your veterinarian (some specific brands like Dilacor XR are sometimes opened to use the tablets inside, but only under strict veterinary guidance).
- Side Effects: Watch for signs of lethargy, weakness, fainting, or vomiting (especially common in cats). Contact your veterinarian immediately if your pet collapses or seems unusually tired.
- Consistency: Heart medications require strict adherence to the dosing schedule. Do not skip doses or stop the medication abruptly without consulting your vet.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.