Quinidine: veterinary dose and monograph

At a glance

Drug class

Cardiovascular

Also known as

Quinidine sulphate, Quinidine gluconate, Quinaglute

Species with doses

Dogs, Cats, Cattle and Horses

Routes

PO, IV, IM

Last reviewed

1 October 2026

Indications

• Atrial fibrillation conversion in horses (quinidine sulphate PO / gluconate IV) — the classic protocol
• Refractory supraventricular/ventricular arrhythmias (occasionally)

Quinidine 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

• Ventricular/atrial arrhythmia (uncommon): Papich 5e (as base): sulfate 6–20 mg/kg PO q6–8h or 5–10 mg/kg IV q6h; gluconate 6–20 mg/kg IM q6h or PO q6–8h. Plumb’s p.1036: 6.6–22 mg/kg PO q6–8h (Ettinger); 6–16 mg/kg PO q6h, sustained-release 8–20 mg/kg q8h (Ware). Rarely used now; ECG monitoring.
• Atrial fibrillation conversion (no structural heart disease): Plumb’s p.1036 (Russell & Rush; Smith 2009): quinidine gluconate 6–11 mg/kg IM q6h; some dogs convert within 24 h. Slow a rapid ventricular response with digoxin or a beta-blocker.

Cats

• Arrhythmia: Plumb’s p.1036 (Ware 2000): 6–16 mg/kg IM or PO q8h. ECG monitoring.

Cattle

• Atrial fibrillation: Papich 5e: poorly absorbed orally in cattle — give IV: 49 mg/kg over 4 h followed by 42 mg/kg maintenance, or 40 mg/kg in 4 L fluid at 1 L/h until conversion. Obtain a FARAD withdrawal.

Horses

• Atrial fibrillation conversion (quinidine sulphate via NG tube): Plumb’s p.1036: quinidine sulfate 22 mg/kg via nasogastric tube every 2 h until conversion, toxicity or 4–6 doses, then q6h (Kimberly & McGurrin; Risberg); fast 12 h first; dissolve in 1–2 L water. Papich 5e: 5 g per 450 kg first, then 10 g per 450 kg q2h. Stop if QRS exceeds 125% of baseline, heart rate >80–100 bpm, ventricular arrhythmias, nasal oedema or urticaria. Specialist procedure with continuous ECG; hypokalaemia increases torsades risk.
• Recent-onset AF / V-tach (quinidine gluconate IV): Plumb’s p.1036: 0.5–2.2 mg/kg IV boluses every 5–10 min to effect, maximum 12 mg/kg (Kimberly & McGurrin); AF <7 days or under anaesthesia 1.1–2.2 mg/kg every 10 min to 8.8–11 mg/kg (Mogg). Papich 5e: 1–1.5 mg/kg every 10–15 min to 10 mg/kg. Continuous ECG.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Atrial fibrillation: Papich 5e: poorly absorbed orally in cattle — give IV: 49 mg/kg over 4 h followed by 42 mg/kg maintenance, or 40 mg/kg in 4 L fluid at 1 L/h until conversion. Obtain a FARAD withdrawal.

Contraindications

Significant structural heart disease / congestive heart failure, high-grade AV block, marked QT prolongation, and digoxin toxicity. Use without continuous ECG monitoring (proarrhythmic). Known cinchona/quinidine hypersensitivity. Concurrent QT-prolonging drugs. Specialist supervision required.

Species-specific warnings

Horses: AF conversion with quinidine is a specialist, ECG-monitored procedure with real proarrhythmic and laminitis risk — not a routine field treatment.

Adverse effects

• GI: diarrhoea, colic, anorexia (horses)
• Hypotension, QRS/QT prolongation, proarrhythmia (torsades, sudden ventricular/supraventricular tachycardia)
• Nasal mucosal swelling, ataxia, depression, urticaria (horses)
• Laminitis; "cinchonism" (CNS signs); thrombocytopenia

Drug interactions

• Digoxin: quinidine markedly RAISES digoxin levels (reduce digoxin, monitor) — a classic, dangerous interaction
• Other QT-prolonging/antiarrhythmic drugs: additive proarrhythmia
• Anticholinergics: additive (quinidine is vagolytic)
• Drugs altering urine pH / CYP: affect quinidine levels

Pregnancy and lactation

Limited data; use only if the maternal arrhythmia risk clearly outweighs fetal risk, under specialist care.

Monitoring

• Continuous ECG during conversion — QRS width (stop if widening >25 %), QT, heart rate and rhythm
• Blood pressure; GI and neurologic signs
• Plasma quinidine levels where available; digoxin levels if co-administered
• Laminitis surveillance (horses)

Toxicity and overdose

Narrow margin with serious toxicity: GI signs, hypotension, marked QRS/QT prolongation, dangerous proarrhythmia (torsades, paradoxical rapid supraventricular rates as AV conduction improves), ataxia/CNS signs ("cinchonism"), laminitis and sudden death. Continuous ECG and plasma-level/side-effect monitoring are essential during equine conversion.

Management: Stop the drug. IV sodium bicarbonate for severe QRS widening (sodium-channel-blocker toxicity), IV magnesium for torsades, fluids/vasopressors for hypotension, and supportive cardiac care with continuous ECG. Manage hyperkalaemia and acid–base. Specialist/intensive management.

Clinical pearls

• The classic equine atrial-fibrillation conversion drug — but a NARROW-margin, proarrhythmic agent: do it as a specialist, continuously ECG-monitored procedure (watch QRS widening, heart rate and side effects)
• Remember the digoxin interaction — quinidine sharply raises digoxin levels (halve digoxin, monitor)
• Newer options/electrical cardioversion are increasingly used; quinidine remains a traditional pharmacologic choice for equine AF
• Stop for QRS widening >25 %, dangerous tachyarrhythmia, or significant systemic toxicity

Mechanism of action

A class IA antiarrhythmic that blocks fast sodium channels (slowing conduction/phase-0 depolarisation) and potassium channels (prolonging the action potential and refractory period), interrupting the re-entrant circuits that sustain atrial fibrillation and allowing conversion to sinus rhythm. It also has vagolytic (anticholinergic) and alpha-adrenergic-blocking effects (contributing to its tachycardia/hypotension side effects). The potassium-channel effect prolongs QT — the basis of its proarrhythmic (torsades) risk.

Formulations and products

• Quinidine sulphate 200 mg tablet/powder (oral, horses via NG tube)
• Quinidine gluconate injection (IV)
• Quinidine sulphate / gluconate — 200 mg tablet; injection, Tablet / injection (human-label)

Storage

Tablets/injection: 15–30 °C, protect from light.

Before you use this dose

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.

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Frequently asked questions