Quinidine
Quinidine is a class ia antiarrhythmic.
Group
Class Ia antiarrhythmic
Mechanism of Action
Blocks fast sodium channels, slowing cardiac depolarization and conduction.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Arrhythmia with gluconate | 6–20 mg/kg | IM | Every 6 h | Expressed as quinidine base. |
| Arrhythmia with gluconate | 6–20 mg/kg | PO | Every 6–8 h | Quinidine base. |
| Arrhythmia with polygalacturonate | 6–20 mg/kg | PO | Every 6 h | Quinidine base. |
| Arrhythmia with sulfate | Reference only | PO | Reported oral interval reads q68h, which is ambiguous; amount 6-20 mg/kg as base is retained without guessing an interval. | |
| Arrhythmia with sulfate | 5–10 mg/kg | IV | Every 6 h | Reported states dose as quinidine base. |
Cattle
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Atrial fibrillation | Reference only | IV | Reported gives 49 mg/kg IV over 4 hours then 42 mg/kg maintenance without timing, or 40 mg/kg in 4 L fluid at 1 L/hour until conversion. Do not generalize these linked protocols to bolus dosing. |
Horses
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Atrial fibrillation IV conversion | Reference only | IV | 1-1.5 mg/kg IV every 10-15 minutes until sinus rhythm or cumulative 10 mg/kg. Cumulative course cap is not a per-dose cap. | |
| Atrial fibrillation oral conversion — Initial | 11.1111111111 mg/kg | PO | Once | 5 g per 450 kg via stomach tube; ECG and blood-pressure monitoring required. |
| Atrial fibrillation oral conversion — Maintenance | 22.2222222222 mg/kg | PO | Every 2 h | 10 g per 450 kg every 2 hours until sinus rhythm; stop on conversion or adverse effects. |
Indications
- Selected ventricular arrhythmias
- Atrial fibrillation conversion
Contraindications
- Underlying cardiac disease requires caution.
Interactions
- Inhibits P-glycoprotein and can increase digoxin and other substrate concentrations.
Adverse effects
- Gastrointestinal effects, hypotension, tachyarrhythmias and occasional sudden cardiac death.
Toxicity
Overdose causes conduction abnormalities, hypotension, tachyarrhythmias and delayed CNS effects including seizures. Maintain continuous ECG and hemodynamic monitoring; advanced support may be required.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Quinidine gluconate 324 mg tablet 324 mg salt contains the stated 202 mg quinidine base. | Tablet | 202 mg / tablet | PO |
| Quinidine polygalacturonate 275 mg tablet 275 mg salt contains the stated 167 mg quinidine base. | Tablet | 167 mg / tablet | PO |
| Quinidine sulfate 300 mg tablet 300 mg salt contains the stated 250 mg quinidine base. | Tablet | 250 mg / tablet | PO |
Monitoring and Administration
Continuous ECG and blood-pressure assessment are essential during conversion. Dose basis is quinidine base; commercial salt amounts differ.
Protect from light and discard darkened preparations; reported oral syrup stability is 60 days.
New quinidine gluconate/sulfate tables include canine 6.6-22 mg/kg and feline 6-16 mg/kg regimens without consistently saying salt or base; they are not merged into base-normalized entries. One sulfate oral interval is clearly every 6-8 hours, resolving the earlier printed q68h schedule, but the amount basis still needs qualification.
Equine cardioversion protocols require ECG-guided cumulative limits: gluconate IV 0.5-2.2 mg/kg every 5-10 minutes to totals 8.8-12 mg/kg; sulfate 22 mg/kg by nasogastric tube every 2 hours for 4-6 doses, then every 6 hours if needed. Salt basis differs from base-normalized prior regimens. Stop for significant tachycardia, QRS widening above 125% baseline or other toxicity; hypokalemia increases torsades risk.
Only clear, colorless quinidine gluconate injection is suitable; discard darkened material and use a slow, monitored infusion.