Verapamil
Verapamil hydrochloride
Also known as: Calan · Isoptin · Verelan · Covera-HS · Securon · CP-16533-1 · D-365 · iproveratril hydrochloride · verapamili hydrochloridum
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 |
|---|---|---|---|---|---|
| Supraventricular tachycardia | Initial dose of 0.05 mg/kg IV slowly, can repeat every 5 minutes up to a total dose of 0.15-0.2 mg/kg; Oral Dose: 0.5-2 mg/kg PO q8h | IV/PO | q8h (for PO) | — | 🌎 NA |
| Treatment of hypertension | 1-5 mg/kg PO q8h | PO | q8h | — | 🌎 NA |
| Emergency treatment for hemodynamically unstable and sustained (continuous) supraventricular tachycardia | 0.05 mg/kg boluses IV (slowly) up to a total dose of 0.15 mg/kg | IV | Series of boluses | — | 🌎 NA |
| General arrhythmias | 1-5 mg/kg PO three times daily; 0.05-0.25 mg/kg IV slowly | PO/IV | TID (for PO) | — | 🌎 NA |
| Acute termination of supraventricular tachycardia | Initial dose of 0.05 mg/kg should be administered over 1-2 minutes while ECG is monitored; if not effective, may repeat in 5-10 minutes. If arrhythmia still not terminated, may give one last dose of 0.05 mg/kg (total = 0.15 mg/kg). For longer control, may give as a CRI at 2-10 micrograms/kg/minute. | IV | PRN / CRI | — | 🌎 NA |
| Supraventricular tachyarrhythmias | 0.5-3 mg/kg | PO | q8h | — | 🌍 EU |
| Supraventricular tachyarrhythmias (Acute) | 0.05 mg/kg | IV | once | over 5 minutes | 🌍 EU |
- Emergency treatment for hemodynamically unstable and sustained (continuous) supraventricular tachycardia: As an alternative to diltiazem
- Acute termination of supraventricular tachycardia: Effect may persist for 30 minutes or less.
- Supraventricular tachyarrhythmias (Acute): Administer slowly with ECG monitoring. Up to 4 repeat IV administrations at a reduced dose of 0.025 mg/kg q5min if necessary.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Supraventricular tachycardia | Initial dose of 0.025 mg/kg IV slowly, can repeat every 5 minutes up to a total dose of 0.15-0.2 mg/kg; Oral Dose: 0.5-1 mg/kg PO q8h | IV/PO | q8h (for PO) | — | 🌎 NA |
| Supraventricular tachyarrhythmias | 0.5-1 mg/kg | PO | q8h | — | 🌍 EU |
| Supraventricular tachyarrhythmias (Acute) | 0.025 mg/kg | IV | once | over 5 minutes | 🌍 EU |
- Supraventricular tachyarrhythmias (Acute): Administer slowly with ECG monitoring. Up to 3 repeat IV administrations q5min if necessary.
Small Mammals
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Cardiovascular disease | 0.25-0.5 mg (total dose per hamster) SC | SC | — | — | 🌎 NA |
| Cardiovascular disease | 8-16 mg/kg PO + 0.5-2 mg/kg SC once daily (q24h) | PO/SC | q24h | — | 🌎 NA |
- Cardiovascular disease: Hamsters
- Cardiovascular disease: Rabbits
Horses
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| To control ventricular rate in atrial fibrillation | 0.025-0.05 mg/kg IV q 30 minutes; give less than 0.2 mg/kg total dose | IV | q 30 minutes | — | 🌎 NA |
- To control ventricular rate in atrial fibrillation: ARCI UCGFS CLASS 4 DRUG
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Verapamil is a non-dihydropyridine calcium channel blocker and a Class IV antiarrhythmic agent.
Unlike dihydropyridine calcium channel blockers (such as amlodipine) which primarily target vascular smooth muscle to cause vasodilation, verapamil has profound effects on the cardiac conduction system, specifically the atrioventricular (AV) node.
Key Clinical Uses:
- Primarily utilized in veterinary medicine to manage supraventricular tachycardias (SVT) in dogs and cats.
- May be used for rate control in atrial flutter or atrial fibrillation.
- Clinical Pearl: Verapamil is a known inhibitor of P-glycoprotein (P-gp). Because of this mechanism, it is currently being investigated as an adjunctive treatment for pharmaco-resistant epilepsy to help prevent the efflux of antiepileptic drugs from the central nervous system.
Mechanism of action
Verapamil exerts its effects by blocking the transmembrane influx of extracellular calcium ions through L-type voltage-gated calcium channels in myocardial cells and vascular smooth muscle cells.
- Cardiac Conduction (Primary Effect): Blocks calcium channels in the SA and AV nodes → decreases AV node conduction velocity and increases the effective refractory period → slows ventricular response rate in supraventricular arrhythmias.
- Myocardial Contractility: Exhibits a negative inotropic effect (decreases heart muscle contractility).
- Vascular Smooth Muscle: Inhibits contractile mechanisms → causes vasodilation and decreases peripheral vascular resistance (though less potently than amlodipine).
- Neurological: Inhibits P-glycoprotein (MDR1/ABCB1) at the blood-brain barrier → reduces the efflux of certain substrate drugs back into the systemic circulation.
Safety & warnings
Contraindications
- Cardiogenic shock
- Severe CHF (unless secondary to a supraventricular tachycardia amenable to verapamil)
- Hypotension (<90 mmHg systolic)
- Sick sinus syndrome
- 2nd or 3rd degree AV block
- Digoxin intoxication
- Hypersensitivity to verapamil
- Recent use (within a few hours) of IV beta-adrenergic blockers
- Left ventricular dysfunction
- Heart failure
Adverse effects
- Hypotension
- Bradycardia
- Tachycardia
- Exacerbation of congestive heart failure (CHF)
- Peripheral edema
- AV block
- Pulmonary edema
- Nausea
- Constipation
- Dizziness
- Headache
- Fatigue
- Precipitation or exacerbation of congestive heart failure
Precautions
Critical Warning: IV verapamil is contraindicated within a few hours of IV beta-adrenergic blocking agents (e.g., propranolol). The combination can severely depress myocardial contractility and AV node conduction, potentially causing rapid hemodynamic deterioration and ventricular fibrillation.
- Cardiac Disease: Use with caution in patients with heart failure or hypertrophic cardiomyopathy (HCM) due to negative inotropic effects.
- Organ Impairment: Toxicity may be potentiated in patients with hepatic or renal impairment.
- Arrhythmias: Use very cautiously in patients with atrial fibrillation and Wolff-Parkinson-White (WPW) syndrome as fatal arrhythmias may result.
- Endocrine: May increase blood glucose in dogs; use with caution in diabetic animals.
- Breed Sensitivities: Verapamil is a neurotoxic substrate of P-glycoprotein. Use with extreme caution in herding breeds (e.g., Collies, Australian Shepherds) that may possess the MDR1 (ABCB1) gene mutation causing a nonfunctional P-gp protein.
Drug interactions
May cause additive hypotensive effects
May cause additive hypotensive effects
May cause additive negative cardiac inotrope and chronotrope effects; IV combination is contraindicated
Verapamil may increase doxorubicin concentrations
May decrease oral absorption of verapamil
Verapamil may increase cyclosporine levels
Cardiovascular collapse reported in animals when used with verapamil
Verapamil may increase blood levels of digoxin; monitoring recommended
May cause additive effects and impair left ventricular function; concurrent use within 24-48 hours not recommended
May cause additive hypotensive effects
May increase verapamil levels
Possible additive effects; concurrent use is to be avoided in humans
Effects of nondepolarizing muscle relaxants may be enhanced by verapamil
May reduce verapamil levels
Additive alpha-adrenergic blocking activity; increased hypotensive effect; verapamil can block quinidine's AV conductive effects and increase quinidine levels
May reduce verapamil levels
Verapamil may increase serum levels of theophylline and lead to toxicity
Calcium channel blockers may increase intracellular vincristine by inhibiting the drug's outflow from the cell
Profound negative inotropic and chronotropic effect
May lead to cardiovascular depression and hypotension
May adversely affect verapamil activity
May increase the effects of verapamil
May increase blood levels leading to potentially toxic effects
Neuromuscular blocking effects may be enhanced
Monitoring
- Clinical signs of toxicity (hypotension, bradycardia, edema)
- Blood pressure (especially during acute IV therapy)
- Serum concentration (if efficacy or toxicity warrant; 100-300 ng/mL is considered therapeutic)
- ECG (especially during IV administration)
- Heart rate and rhythm
- Liver function (in patients with hepatic disease)
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed after oral administration (~90%), but undergoes a high first-pass effect in the liver, resulting in systemic bioavailability of only 20-30%. Hepatic dysfunction can significantly increase bioavailability. Food decreases the rate and extent of absorption of sustained-release tablets.
Distribution
Volume of distribution is approximately 4.5 L/kg in dogs. Highly protein-bound (~90% in humans). Crosses the placenta and enters milk at levels approaching plasma concentrations.
Metabolism
Extensively metabolized in the liver to at least 12 separate metabolites, with norverapamil being the predominant active metabolite.
Elimination
The majority of metabolites are excreted in the urine. Only 3-4% is excreted unchanged in the urine.
Overdose
Clinical Signs of Overdose: Bradycardia, hypotension, hyperglycemia, junctional rhythms, and 2nd or 3rd degree AV block.
Treatment:
- Decontamination: If secondary to recent oral ingestion, consider gut emptying and activated charcoal administration.
- Supportive Care: Vigorously monitor cardiac and respiratory function.
- Negative Inotropy: Intravenous calcium salts (1 mL of 10% solution per 10 kg of body weight) may treat negative inotropic signs, but may not adequately resolve heart block.
- Hypotension: Fluid therapy and pressor agents (e.g., dopamine, norepinephrine) may be utilized.
- AV Block / Bradycardia: Treat with isoproterenol, norepinephrine, atropine, or cardiac pacing.
- Rapid Ventricular Rate: Patients developing rapid ventricular rate due to antegrade conduction in flutter/fibrillation with WPW syndrome have been treated with D.C. cardioversion, lidocaine, or procainamide.
Available products
Formulations
- Sustained/Extended-Release Tablets
- Sustained/Extended-Release Capsules
- Injection
- Injectable: 2.5 mg/ml solution
- Oral: 40 mg, 80 mg, 120 mg, 160 mg tablets
- Oral: 40 mg/5 ml oral solution
Veterinary
- None
Human-labeled
- Verapamil HCl Tablets: 40 mg, 80 mg & 120 mg (Calan®, generic)
- Verapamil HCl Sustained/Extended-Release Tablets/Capsules: 100 mg, 120 mg, 180 mg, 200 mg, 240 mg, 300 mg & 360 mg (Calan® SR, Covera-HS®, Isoptin® SR, Verelan®, Verelan® PM, generic)
- Verapamil HCl for Injection: 2.5 mg/mL in 2 mL & 4 mL vials, amps and syringes (generic)
- Securon (2.5 mg/ml injectable)
- Verapamil (40 mg, 80 mg, 120 mg, 160 mg tablets; 40 mg/5 ml oral solution)
Regulatory status
Human authorized products used under the cascade.
POM (Prescription Only Medicine)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Verapamil HCl tablets should be stored at room temperature (15-30°C). The injectable product should be stored at room temperature (15-30°C) and protected from light and freezing.
Client information
Verapamil is a medication used primarily to correct abnormally fast heart rhythms.
- Compliance is Key: To be effective, your pet must receive all doses exactly as prescribed by your veterinarian. Do not skip doses or stop the medication abruptly.
- What to Watch For: Contact your veterinarian immediately if your pet becomes unusually lethargic, shows exercise intolerance, begins wheezing, has shortness of breath or a cough, or develops any sudden change in behavior or attitude.
- Dietary Notes: Follow your veterinarian's instructions regarding giving this medication with or without food, as food can affect how certain formulations are absorbed.
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.