# Diltiazem: veterinary dose and monograph

> Diltiazem is a veterinary cardiovascular drug. Class IV antiarrhythmic — a non-dihydropyridine calcium-channel blocker that slows AV-nodal conduction and causes coronary vasodilation with relatively little negative inotropy. Indications include rate control of atrial fibrillation / supraventricular tachycardia; feline hypertrophic cardiomyopathy; systemic hypertension (adjunct). This monograph lists 8 reference doses for dogs, cats, horses and rabbits, each with route, frequency and source.

Source: https://vetmasterji.com/drugs/diltiazem · Last reviewed: 2026-10-01

## At a glance

- **Drug class:** Cardiovascular
- **Also known as:** Cardizem, Dilacor, Dilzem
- **Species with doses:** Dogs, Cats, Horses and Rabbits
- **General dose range:** 0.5–2.5 mg/kg PO q8h (or sustained-release q12–24h) — check the species tables for the indication
- **Routes:** PO, IV
- **Last reviewed:** 1 October 2026

## Indications

- Rate control of atrial fibrillation / supraventricular tachycardia
- Feline hypertrophic cardiomyopathy
- Systemic hypertension (adjunct)

## Diltiazem dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

### Dogs

*Diltiazem doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| AF rate control | 0.5–1.5 mg/kg | PO | q8h; titrate to heart rate | — |
| Acute rate control | 0.05–0.25 mg/kg | IV | slow IV over 2 min; repeat to effect | — |
| SVT — CRI | 0.1–0.4 mg/kg/h | IV | CRI after 0.15–0.25 mg/kg IV over 2 min | — |

- AF rate control: Papich 5e: 0.5–1.5 mg/kg q8h PO for most uses; for atrial fibrillation doses up to 5 mg/kg q12h have been used as monotherapy, or 3 mg/kg q12h with digoxin 0.005 mg/kg q12h. Plumb’s p.407 (Kittleson 2010): add to digoxin when rate control is inadequate — start 0.5 mg/kg PO q8h, increase to 1 then 1.5 mg/kg q8h; avoid in moderate–severe myocardial failure and do not combine with a beta-blocker.
- Acute rate control: Papich 5e: AF 0.05–0.25 mg/kg IV every 5 min to effect; SVT 0.25 mg/kg over 2 min, wait 20 min before repeating. Plumb’s p.407: 0.05 mg/kg IV over 1–2 min, up to 3 doses 5 min apart (Kittleson); 0.05–0.15 mg/kg every 5 min to a total of 0.1–0.3 mg/kg (Ware); 0.25 mg/kg every 15 min to a maximum total of 0.75 mg/kg (Rush 2005). ECG and blood pressure monitoring.
- SVT — CRI: Papich 5e: 0.15–0.25 mg/kg IV over 2 min, then CRI 0.1–0.2 mg/kg/h, up to a maximum of 0.4 mg/kg/h.

### Cats

*Diltiazem doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| HCM / SVT | 1.75–2.5 mg/kg | PO | q8h | — |
| HCM — extended-release capsules (Cardizem CD) | 10 mg/kg | PO | q24h | — |
| Acute SVT (IV) | 0.125–0.35 mg/kg | IV | slow IV; repeat q15 min to max 0.75 mg/kg total | — |

- HCM / SVT: Immediate-release tablets. Papich 5e: 1.75–2.4 mg/kg q8h PO — commonly 7.5–10 mg per cat q8h, reduced to q12h in some cats. Plumb’s p.407: 1.75–2.5 mg/kg PO q8h (Ware & Keene 2000); 7.5–15 mg per cat q8h (Kittleson).
- HCM — extended-release capsules (Cardizem CD): Papich 5e and Plumb’s p.407 (Fox 2000): Cardizem CD or Dilacor XR 10 mg/kg once daily; Dilacor XR is often given as 30 mg per cat q12–24h (½ of a 60 mg tablet from the capsule) — 30 mg caused fewer adverse effects than 60 mg. Papich: slow-release products give inconsistent levels in cats.
- Acute SVT (IV): Plumb’s p.407: acute management 0.125–0.35 mg/kg IV (Wright 2000); 0.25 mg/kg IV over 2 min, repeated every 15 min to a maximum total of 0.75 mg/kg (Rush 2005). ECG monitoring.

### Horses

*Diltiazem doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Supraventricular tachyarrhythmia | 0.125 mg/kg | IV | over ≥2 min, repeat q10 min to 1.1 mg/kg total | — |

- Supraventricular tachyarrhythmia: Papich 5e: 0.125 mg/kg IV over at least 2 minutes, repeated every 10 minutes as needed up to a total of 1.1 mg/kg. ECG monitoring.

### Rabbits

*Diltiazem doses for rabbits*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Hypertrophic cardiomyopathy / supraventricular arrhythmia | 0.5–1 mg/kg | PO | q12–24h | — |

- Hypertrophic cardiomyopathy / supraventricular arrhythmia: Carpenter's 6th ed (Rabbit cardiovascular table): 0.5–1 mg/kg PO q12–24h — calcium-channel blocker to slow rate / treat SV and ventricular arrhythmias.

## Contraindications

Significant AV block / sick sinus syndrome, hypotension, severe systolic dysfunction, concurrent IV beta-blocker (additive AV block / bradycardia).

## Adverse effects

- Bradycardia, hypotension, AV block
- Anorexia / GI upset
- Lethargy

## Drug interactions

- Beta-blockers: increased likelihood of bradycardia, AV block or CHF (including with OPHTHALMIC beta-blockers, which are easy to overlook); diltiazem may also substantially increase the bioavailability of propranolol
- General anaesthetics: may increase the cardiac depressant effects of diltiazem
- Digoxin: data conflict on whether diltiazem alters digoxin kinetics — perform diligent digoxin level monitoring if combined
- Cimetidine: may increase plasma diltiazem concentrations — increase monitoring; ranitidine has a lesser effect
- Cyclosporine: diltiazem may increase cyclosporine concentrations — monitor and adjust
- Quinidine: diltiazem may increase quinidine concentrations — monitor and adjust
- Benzodiazepines: diltiazem may increase benzodiazepine levels
- Buspirone: levels may be increased
- Cisapride: potential for increased QT interval
- Rifampin: may DECREASE diltiazem levels

## Toxicity and overdose

Plumb's p.406: oral LD50 in dogs is reported as >50 mg/kg. Overdose signs are GI upset, heart block, bradycardia, hypotension and heart failure. A documented case (Syring et al. 2008): a dog that ingested about 100 mg/kg of a SUSTAINED-RELEASE product developed bradycardia, hypotension, CNS depression, second-degree AV block with ventricular escape and GI signs, and required a transvenous pacemaker for 19 hours before recovering — sustained-release formulations make these ingestions both delayed and prolonged. Management: gut emptying where warranted plus supportive care. ATROPINE for bradycardia or 2nd/3rd degree AV block; if unresponsive to vagal blockade, isoproterenol may be tried cautiously; fixed block may need cardiac pacing. Inotropes (dobutamine, dopamine, isoproterenol) and pressors (dopamine, norepinephrine) for heart failure and hypotension. A slow IV calcium infusion — 1 mL/10 kg of 10% calcium gluconate — may also help in severe acute toxicity.

## Clinical pearls

- Preferred over verapamil and nifedipine in a compromised heart: its negative inotropy is rarely clinically important, theirs is
- Sustained-release overdoses behave very differently from immediate-release — expect delayed, prolonged signs and consider pacing
- Often combined with digoxin for AF — diltiazem controls rate during exercise, digoxin at rest
- Sustained-release formulations improve compliance in cats but absorption varies — recheck heart rate after switching
- Titrate to a target heart rate, not a fixed dose; watch for hypotension and bradycardia

## Mechanism of action

Plumb's p.406: calcium-channel blocker, similar in action to verapamil and nifedipine. The exact mechanism is unknown, but it inhibits transmembrane influx of extracellular calcium into myocardial cells and vascular smooth muscle WITHOUT altering serum calcium concentrations. Net effect: inhibited cardiac and vascular smooth-muscle contractility, dilating the main systemic and coronary arteries, so total peripheral resistance, blood pressure and cardiac afterload all fall. On conduction it SLOWS AV nodal conduction and prolongs refractory times — the basis of its use in supraventricular tachyarrhythmias. It rarely affects SA node conduction, though resting heart rate may drop in Sick Sinus Syndrome. Crucially, although diltiazem has negative inotropic potential this is RARELY clinically important, unlike verapamil or nifedipine — which is why diltiazem is the calcium-channel blocker of choice in a compromised heart.

## Formulations and products

- Diltiazem 30 mg tablet
- Diltiazem 60 mg tablet
- Diltiazem 5 mg/mL injection

## Before you use this dose

> **Caution:** Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

## Other cardiovascular drugs

- [Benazepril](https://vetmasterji.com/drugs/benazepril)
- [Captopril](https://vetmasterji.com/drugs/captopril)
- [Carvedilol](https://vetmasterji.com/drugs/carvedilol)
- [Digoxin](https://vetmasterji.com/drugs/digoxin)
- [Dobutamine](https://vetmasterji.com/drugs/dobutamine)
- [Dopamine](https://vetmasterji.com/drugs/dopamine)
- [Enalapril](https://vetmasterji.com/drugs/enalapril)
- [Esmolol](https://vetmasterji.com/drugs/esmolol)

## Frequently asked questions

### What is the dose of Diltiazem for dogs?

Reference doses for Diltiazem in dogs: 0.5–1.5 mg/kg PO q8h; titrate to heart rate (AF rate control); 0.05–0.25 mg/kg IV slow IV over 2 min; repeat to effect (Acute rate control); 0.1–0.4 mg/kg/h IV CRI after 0.15–0.25 mg/kg IV over 2 min (SVT — CRI). Confirm against the label and the patient before use.

### What is the dose of Diltiazem for cats?

Reference doses for Diltiazem in cats: 1.75–2.5 mg/kg PO q8h (HCM / SVT); 10 mg/kg PO q24h (HCM — extended-release capsules (Cardizem CD)); 0.125–0.35 mg/kg IV slow IV; repeat q15 min to max 0.75 mg/kg total (Acute SVT (IV)). Confirm against the label and the patient before use.

### What is the dose of Diltiazem for horses?

Reference doses for Diltiazem in horses: 0.125 mg/kg IV over ≥2 min, repeat q10 min to 1.1 mg/kg total (Supraventricular tachyarrhythmia). Confirm against the label and the patient before use.

### When should Diltiazem not be used?

Significant AV block / sick sinus syndrome, hypotension, severe systolic dysfunction, concurrent IV beta-blocker (additive AV block / bradycardia).

### What are the side effects of Diltiazem in animals?

Bradycardia, hypotension, AV block; Anorexia / GI upset; Lethargy.

## Sources

- Plumb's Veterinary Drug Handbook
- Papich, Papich Handbook of Veterinary Drugs, 5th edition
- Carpenter, Exotic Animal Formulary

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VetMasterJi is a clinical decision-support and education platform for veterinary professionals and students. It does not provide veterinary advice, diagnosis or treatment for specific animals. All drug doses, calculators and differentials are references that must be independently verified before clinical use; the attending registered veterinarian remains solely responsible for every clinical decision.