# Quinidine: veterinary dose and monograph

> Quinidine is a veterinary cardiovascular drug. A class IA antiarrhythmic whose classic veterinary role is CONVERSION of ATRIAL FIBRILLATION in HORSES (quinidine sulphate by nasogastric tube, or quinidine gluconate IV for acute AF) — for decades the standard pharmacologic cardioversion… Indications include atrial fibrillation conversion in horses (quinidine sulphate PO / gluconate IV) — the classic protocol; refractory supraventricular/ventricular arrhythmias (occasionally). This monograph lists 6 reference doses for dogs, cats, cattle and horses, each with route, frequency and source, plus meat and milk withdrawal periods for food animals.

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

## 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

*Quinidine doses for dogs*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Ventricular/atrial arrhythmia (uncommon) | 6–20 mg/kg | PO | q6–8h | — |
| Atrial fibrillation conversion (no structural heart disease) | 6–11 mg/kg | IM | q6h | — |

- 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

*Quinidine doses for cats*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Arrhythmia | 6–16 mg/kg | PO | q8h | — |

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

### Cattle

*Quinidine doses for cattle*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Atrial fibrillation | 40–49 mg/kg | IV | slow infusion (≈4 h) | — | Withdrawal NOT established — treat as extra-label |

- 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

*Quinidine doses for horses*

| Indication | Dose | Route | Frequency | Duration |
| --- | --- | --- | --- | --- |
| Atrial fibrillation conversion (quinidine sulphate via NG tube) | 22 mg/kg | PO | q2h via NG tube for 4–6 doses (88–132 mg/kg total), then q6h if needed | — |
| Recent-onset AF / V-tach (quinidine gluconate IV) | 0.5–2.2 mg/kg | IV | every 5–10 min to a total of 8.8–12 mg/kg | — |

- 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.

*Quinidine doses for buffalo*

| Indication | Dose | Route | Frequency | Duration | Withdrawal |
| --- | --- | --- | --- | --- | --- |
| Atrial fibrillation | 40–49 mg/kg | IV | slow infusion (≈4 h) | — | Withdrawal NOT established — treat as extra-label |

- 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

> **Caution:** 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

> **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.

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## Frequently asked questions

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

Reference doses for Quinidine in dogs: 6–20 mg/kg PO q6–8h (Ventricular/atrial arrhythmia (uncommon)); 6–11 mg/kg IM q6h (Atrial fibrillation conversion (no structural heart disease)). Confirm against the label and the patient before use.

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

Reference doses for Quinidine in cats: 6–16 mg/kg PO q8h (Arrhythmia). Confirm against the label and the patient before use.

### What is the dose of Quinidine for cattle?

Reference doses for Quinidine in cattle: 40–49 mg/kg IV slow infusion (≈4 h) (Atrial fibrillation). Confirm against the label and the patient before use.

### What is the withdrawal period for Quinidine?

Cattle, IV (Atrial fibrillation): Withdrawal NOT established — treat as extra-label. Follow the product label and national regulations where they differ.

### When should Quinidine not be used?

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.

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

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.

## Sources

- Plumb's Veterinary Drug Handbook
- Merck Veterinary Manual, 11th edition
- Papich, Papich Handbook of Veterinary Drugs, 5th edition

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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.