Drug information of Quinidine
Quinidine is an antimalarial schizonticide and an antiarrhythmic agent with class 1a activity. ; it is an optical isomer of quinine, extracted from the bark of the Cinchona tree and similar plant species. This alkaloid dampens the excitability of cardiac and skeletal muscles by blocking sodium and potassium currents across cellular membranes. It prolongs cellular action potential, and decreases automaticity. Quinidine also blocks muscarinic and alpha-adrenergic neurotransmission.
Mechanism of effect
Class Ia antiarrhythmic agent; depresses phase 0 of the action potential; decreases myocardial excitability and conduction velocity, and myocardial contractility by decreasing sodium influx during depolarization and potassium efflux in repolarization; also reduces calcium transport across cell membrane
Distribution: Vd: Adults: 2 to 3 L/kg, decreased with congestive heart failure (0.5 L/kg), malaria; increased with cirrhosis.
- Protein binding: Newborns: 50% to 70%; Adults: 80% to 88%
- Binds mainly to alpha 1-acid glycoprotein and to a lesser extent albumin
- Metabolism: Extensively hepatic (50% to 90%) to inactive compounds
- Bioavailability: Sulfate: ~70% with wide variability between patients (45% to 100%); Gluconate: 70% to 80%
- Half-life elimination, plasma: Children: 2.5 to 6.7 hours ; Adults: 6 to 8 hours; prolonged with elderly, cirrhosis, and congestive heart failure
- Excretion: Urine (15% to 25% as unchanged drug)
Dosage Forms & Strengths
200mg (as sulfate)
300mg (as sulfate)
300mg (as sulfate)
324mg (as gluconate)
80mg/mL (as gluconate)
Test Dose: 200 mg PO quinidine sulfate several hr before full dosage
AFib: 300-400 mg PO q6hr
PSVT: 400-600 mg PO q2-3hr until paroxysm terminated
Atrial/Ventricular Premature Contractions: 200-300 mg PO q6-8hr
Maint: 200-400 mg PO q6-8hr or 600 mg of SR PO q8-12hr
No more than 3-4 g/day
324-660 mg PO q8-12hr
Maintenance: 648 mg PO q12hr OR 324-660 mg PO q8hr
PSVT: 400 - 600 mg PO q2-3hr until paroxysm is terminated
IV: Usual <5 mg/kg (but may need up to 10 mg/kg) at 0.25 mg/kg/min
Load: 24 mg/kg diluted in 250 mL NS IV infusion over 4 hours
Maintenance: Follow by 12 mg/kg IV infusion over 4 hours q8hr beginning 8 hr after initiation of loading dose except in patients able to swallow the same doses of quinidine are administered using 300 mg quinidine sulfate tablets
Load: 10 mg/kg diluted in 5 mL/kg NS IV over 1-2 hr
Maintenance: Follow by 0.02 mg/kg/min continuous IV infusion; in patients able to swallow oral quinine is administered every 8 hr to give as much quinine as patient received in quinidine q8hr
PO regimen: 300 mg quinidine or 650 mg quinine PO q8hr for 3 days (Africa and South America) or 7 days (Southeast Asia) or until parasitemia is reduced to 1%
CrCl < 10 mL/min: Administer 75% of normal dose
CrCl ≥10 L/min: Dose adjustment not necessary
Concerns related to adverse effects:
Hepatotoxicity: Has been associated with severe hepatotoxic reactions, including granulomatous hepatitis.
Hypersensitivity reactions: With use, hypersensitivity reactions may occur.
Proarrhythmic effects: Monitor for proarrhythmic effects; may cause QT prolongation and subsequent torsade de pointes. Monitor and adjust dose to prevent QTc prolongation. Avoid use in patients with diagnosed or suspected congenital long QT syndrome.
- Arrhythmias: Appropriate use: Antiarrhythmic drugs have not been shown to enhance survival in non-life-threatening ventricular arrhythmias and may increase mortality; the risk is greatest with structural heart disease. Quinidine may increase mortality in treatment of atrial fibrillation/flutter.
- Atrial fibrillation/flutter: May increase ventricular response rate in patients with atrial fibrillation or flutter; control AV conduction before initiating.
- Conduction disturbances: Use with caution in patients at risk for heart block; can unmask sick sinus syndrome (causes bradycardia).
- Electrolyte imbalance: Correct electrolyte disturbances, especially hypokalemia or hypomagnesemia, prior to use and throughout therapy.
- G6PD deficiency: Hemolysis may occur in patients with G6PD (glucose-6-phosphate dehydrogenase) deficiency.
- Left ventricular dysfunction/heart failure (HF): Use with caution in patients with reduced left ventricular ejection fraction; may precipitate or exacerbate condition.
- Hepatic impairment: Use with caution in patients with hepatic impairment; reduced dosage recommended.
Concurrent drug therapy issues:
Antiarrhythmics: Use with caution with concurrent use of other antiarrhythmics.
Digoxin: Use may cause digoxin-induced toxicity; adjust digoxin's dose.
Dosage form specific issues:
Different salts: Do not interchange the different salt products.
Points of recommendation
Overly rapid infusion of Quinidine may cause peripheral vascular collapse and severe hypotension.
In patients without implanted pacemakers who are at high risk of complete atrioventricular block, Quinidine should be used only with caution.
By a mechanism that is not understood, Quinidine potentiates the anticoagulatory action of warfarin, and the anticoagulant dosage may need to be reduced.