Adult: As quinidine sulfate: Initially, 400 mg 6 hourly, then increase gradually if conversion is not attained after 4 or 5 doses. As quinidine gluconate: 324 mg 8 hourly for 2 days, may increase to 648 mg 12 hourly for 2 days, then increase to 648 mg 8 hourly for up to 4 days if needed. Consider a 4-day duration at a lower dose if higher doses are not tolerated.
Adult: As quinidine sulfate: 200 mg 6 hourly, may increase gradually if needed. As quinidine gluconate: 324 mg 8-12 hourly, may increase gradually to achieve the desired response. Usual dose range: 1,000-1,500 mg daily in 2-3 divided doses.
Administration
Should be taken with food. Best taken at meal times.
Contraindications
Hypersensitivity. History of immune thrombocytopenia or have developed thrombocytopenia purpura before therapy with quinidine or quinine. Heart block >1st degree, idioventricular conduction delays (except in those with a functioning artificial pacemaker); myasthenia gravis or those with conditions affected by anticholinergic activity.
Special Precautions
Patient with structural heart disease, preexisting long-QT syndrome, history of torsades de pointes; significant lengthening of QTc interval after previous quinidine therapy; sick sinus syndrome; electrolyte imbalance (particularly hypokalaemia or hypomagnesaemia); G6PD deficiency. Patients without implanted pacemakers who are at high risk of complete AV block (e.g. digitalis intoxication, 2nd degree AV block, severe intraventricular conduction defects). Use of vagal manoeuvres to terminate paroxysmal supraventricular tachycardia may be ineffective. Renal and hepatic impairment. Pregnancy and lactation.
Adverse Reactions
Significant: Frequent extrasystoles, ventricular tachycardia, ventricular flutter, ventricular fibrillation; paradoxical increase in ventricular rate; vagolysis; thrombocytopenia; haemolysis; hepatotoxicity (including granulomas hepatitis); hypersensitivity reactions. Eye disorders: Visual disturbance. Gastrointestinal disorders: Diarrhoea, gastrointestinal distress, nausea, vomiting, oesophagitis. General disorders and administration site conditions: Fatigue, ataxia, weakness, fever. Nervous system disorders: Dizziness, headache, nervousness, tremor. Skin and subcutaneous tissue disorders: Skin rash. Potentially Fatal: Prolonged QTc interval resulting in torsades de pointes.
Evaluate cardiac status before and during therapy. Monitor ECG, CBC, LFTs, and renal function.
Overdosage
Symptoms: Diarrhoea, vomiting, tinnitus, high-frequency hearing loss, blurred vision, vertigo, diplopia, photophobia, headache, confusion, delirium, ventricular arrhythmias, hypotension. Management: Discontinue treatment and perform immediate cardioversion or, if a cardiac pacemaker is in place or immediately available, perform immediate over drive pacing for ventricular arryhthmias. Replenish central volume (e.g. Trendelenburg positioning, saline infusion), increase peripheral vascular resistance (including α-agonist catecholamines such as norepinephrine and metaraminol) or the Military Anti-Shock Trousers for hypotension.
Drug Interactions
Decreased clearance with diltiazem, verapamil, carbonic anhydrase inhibitors, Na bicarbonate, thiazide diuretics. Increased elimination with phenobarbital, phenytoin, rifampicin. Increased plasma concentration with amiodarone, cimetidine, ketoconazole. Decreased plasma concentration with nifedipine. Increases the serum concentration of digoxin, procainamide, haloperidol. Potentiates the effect of warfarin, depolarising (e.g. succinylcholine, decamethonium) and non-depolarising (e.g. tubocurarine, pancuronium) neuromuscular blocking agents.
Food Interaction
Increased serum concentration with grapefruit juice.
Action
Description: Mechanism of Action: Quinidine is a class Ia antiarrhythmic agent which has an antimalarial property. It depresses phase 0 of the action potential, reduces Na influx during depolarisation and K efflux in repolarisation, thereby decreasing myocardial excitability and conduction velocity, and myocardial contractility. Additionally, it decreases the Ca transport across the cell membrane. Pharmacokinetics: Absorption: Rapidly absorbed from the gastrointestinal tract. Bioavailability: Approx 70% (quinidine sulfate); 70-80% (quinidine gluconate). Time to peak plasma concentration: 2 hours (quinidine sulfate); 3-5 hours (quinidine gluconate). Distribution: Widely distributed throughout the body. Crosses the placenta and enters breast milk. Volume of distribution: 2-3 L/kg. Plasma protein binding: 80-90%, mainly to α1-acid glycoprotein and lesser extent to albumin. Metabolism: Extensively metabolised in the liver by CYP3A4 into several metabolites (inactive). Excretion: Via urine (5-20% as unchanged drug). Elimination half-life: 6-8 hours.
Chemical Structure
Quinidine Source: National Center for Biotechnology Information. PubChem Compound Summary for CID 441074, Quinidine. https://pubchem.ncbi.nlm.nih.gov/compound/Quinidine. Accessed Mar. 25, 2024.
C01BA01 - quinidine ; Belongs to class Ia antiarrhythmics.
References
Anon. Quinidine. AHFS Clinical Drug Information [online]. Bethesda, MD. American Society of Health-System Pharmacists, Inc. https://www.ahfscdi.com. Accessed 05/03/2024.Anon. Quinidine. Lexicomp Online. Hudson, Ohio. Wolters Kluwer Clinical Drug Information, Inc. https://online.lexi.com. Accessed 05/03/2024.Buckingham R (ed). Quinidine. Martindale: The Complete Drug Reference [online]. London. Pharmaceutical Press. https://www.medicinescomplete.com. Accessed 05/03/2024.Quinidine Gluconate Tablet, Extended Release (Eywa Pharma Inc). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 05/03/2024.Quinidine Sulfate Tablet (Epic Pharma, LLC). DailyMed. Source: U.S. National Library of Medicine. https://dailymed.nlm.nih.gov/dailymed. Accessed 05/03/2024.
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