Quinidine Sulfate
Pronunciation: KWIN-i-deen SUL-fate.
- Generic name
- quinidine sulfate
- Brand names
- Quinidine Sulfate, Kinidin Durules, Cardioquin, Quinidine Sulphate, Qunil, Quinaglute
- Drug class
- Class Ia antiarrhythmic
Availability and supply rules vary by country
Trade names by country:
Australia: · Full directory
What quinidine sulfate is and how it works
Uses, formulations, monitoring, and supply rules can differ by patient, product, and country. Follow the exact local product information and professional advice.
Mechanism of action: how quinidine sulfate works
Quinidine sulfate is a class Ia antiarrhythmic agent. It works by blocking fast inward sodium channels during phase 0 of the cardiac action potential, slowing depolarization. It also inhibits potassium channels, prolonging repolarization and the refractory period. This dual action slows conduction velocity and increases the duration of the action potential, reducing the likelihood of abnormal electrical circuits and arrhythmias. (1)
What quinidine sulfate is used for
Ventricular arrhythmias
Ventricular arrhythmias (1)
Supraventricular arrhythmias
Supraventricular arrhythmias (1)
Atrial fibrillation
Atrial fibrillation (1)
Atrial flutter
Atrial flutter (1)
Before taking quinidine sulfate
Do not take / not appropriate for
- hypersensitivity to quinidine or related drugs, complete heart block without a pacemaker, myasthenia gravis, history of torsades de pointes, and prolonged QT interval. (Contraindication) (1)
Tell your clinician about
(1)How to take quinidine sulfate
- General Instructions: Take quinidine sulfate exactly as prescribed by your doctor. Do not take more or less than directed.. Adult Dosing: Typical adult oral dose ranges from 200 mg to 400 mg every 6 to 8 hours, adjusted based on response and blood levels. Dosing may vary depending on the specific arrhythmia being treated.. Pediatric Dosing: Dosing in children is individualized based on weight and clinical response. Pediatric use should be under specialist supervision.. Administration: Take tablets with a full glass of water. Extended-release tablets should be swallowed whole and not crushed or chewed.. When To Stop: Do not stop taking quinidine sulfate suddenly without consulting your doctor, as this may worsen your condition.. Storage: Store at room temperature away from moisture, heat, and light. Keep out of reach of children.
- This page does not provide a dose calculator. Dosing must follow the prescriber, pharmacist, or product label.
Procedures and treatment changes
Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1)
Missed dose
If you miss a dose, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose. Do not double up to make up for a missed dose.
Overdose
In case of overdose, seek emergency medical attention immediately. Symptoms may include severe dizziness, fainting, irregular heartbeat, seizures, or loss of consciousness. Supportive care and monitoring are essential. (1)
Side effects
Side effects and their urgency vary; report severe, persistent, or concerning symptoms to a healthcare professional.
Diarrhea
Incidence: Reported in the clinician-authored database; frequency not established
Nausea
Incidence: Reported in the clinician-authored database; frequency not established
Vomiting
Incidence: Reported in the clinician-authored database; frequency not established
Cinchonism
Incidence: Reported in the clinician-authored database; frequency not established
QT prolongation
Incidence: Reported in the clinician-authored database; frequency not established
Torsades de pointes
Incidence: Reported in the clinician-authored database; frequency not established
Thrombocytopenia
Incidence: Reported in the clinician-authored database; frequency not established
Serious warnings
May cause serious or life-threatening arrhythmias — serious
Symptoms: May cause serious or life-threatening arrhythmias. Risk of severe allergic reactions. Can interact with many other medications. May worsen myasthenia gravis. Requires regular ECG and blood monitoring.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1)
Contraindications recorded in the clinician database — serious
Symptoms: Contraindications recorded in the clinician database: Contraindications include hypersensitivity to quinidine or related drugs, complete heart block without a pacemaker, myasthenia gravis, history of torsades de pointes, and prolonged QT interval. Use with caution in patients with hepatic or renal impairment, electrolyte imbalances, or structural heart disease. Monitor closely in elderly patients.
Action: Follow the urgency stated and seek prompt or emergency care when indicated. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Recorded interactions | Quinidine sulfate interacts with many medications, including digoxin, amiodarone, warfarin, and drugs that prolong the QT interval. It may also interact with certain antibiotics, antifungals, and antidepressants. Always inform your healthcare provider about all medicines and supplements you are taking. | (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
FDA label: quinidine sulfate is classified as Pregnancy Category C — adequate human studies have not been done, and it should be given during pregnancy only if clearly needed. Quinidine is known to cross the placenta (in one reported case, cord blood levels were about 30% of simultaneous maternal levels). Discuss use during pregnancy with the treating clinician. (1)
Breastfeeding
FDA label: quinidine is present in human breast milk at levels slightly lower than maternal blood levels. The label advises avoiding quinidine in breastfeeding women who continue nursing, because of concern about neonatal toxicity related to reduced protein binding in infants. Discuss feeding options with the prescriber before using quinidine while breastfeeding. (1)
Children
Frequency: Not applicable. Weight Based: Not recommended for pediatric use. Max Daily Dose: Not applicable. Max Single Dose: Not applicable. Age Restrictions: Safety not established in children (1)
Renal_impairment
FDA label: both renal and hepatic dysfunction slow quinidine elimination and increase the risk of toxicity, so dosage reduction is generally required in significant renal or hepatic impairment — the exact reduced dose must be individualized by the prescriber, since quinidine has a narrow therapeutic index. Quinidine clearance itself is not directly reduced by cirrhosis, but the volume of distribution increases, prolonging the elimination half-life. (1)
Hepatic_impairment
FDA label: both renal and hepatic dysfunction slow quinidine elimination and increase the risk of toxicity, so dosage reduction is generally required in significant renal or hepatic impairment — the exact reduced dose must be individualized by the prescriber, since quinidine has a narrow therapeutic index. Quinidine clearance itself is not directly reduced by cirrhosis, but the volume of distribution increases, prolonging the elimination half-life. (1)
Monitoring
(1)Storage
Store quinidine sulfate tablets at 20-25°C (68-77°F) in a well-closed, light-resistant container, out of reach of children.
Professional information
Clinician-facing context only. This section does not replace current product labeling.
General
Indication: Ventricular arrhythmias
Dose summary: Initial: 200 mg orally every 8 hours; maintenance: 300-400 mg orally every 8 hours.
Renal context: FDA label: renal dysfunction slows quinidine elimination and can lead to toxicity if the dose is not appropriately reduced. Quinidine undergoes both glomerular filtration and active tubular secretion; urinary pH affects the fraction eliminated unchanged (about 20% at urine pH <7, as little as 5% in more alkaline urine). Dose reduction and individualized monitoring (often with quinidine level and ECG monitoring) are required in significant renal impairment. (1)
Hepatic guidance
FDA label: hepatic dysfunction slows quinidine elimination and increases the risk of toxicity, generally requiring dose reduction. Cirrhosis increases quinidine's volume of distribution, which prolongs its elimination half-life, even though clearance itself is not directly reduced. Individualized dosing and monitoring are required in significant hepatic impairment.
Frequently asked questions
What is quinidine sulfate used for?
Quinidine sulfate is used to treat and prevent certain types of irregular heartbeats (arrhythmias), such as atrial fibrillation, atrial flutter, and some ventricular arrhythmias.
How does quinidine sulfate work?
It works by blocking abnormal electrical signals in the heart, helping to restore and maintain a normal heart rhythm.
What are the most common side effects?
Common side effects include nausea, vomiting, diarrhea, dizziness, and headache. Serious side effects can include irregular heartbeat and severe allergic reactions.
Can I take quinidine sulfate with other heart medications?
Quinidine can interact with many heart medications, including digoxin and amiodarone. Always consult your doctor before combining medications.
What should I do if I miss a dose?
Take the missed dose as soon as you remember, unless it is almost time for your next dose. Do not double up doses.
Is quinidine sulfate safe during pregnancy or breastfeeding?
The safety of quinidine sulfate during pregnancy or breastfeeding is not fully established. Use only if clearly needed and prescribed by your doctor.
How is quinidine sulfate monitored?
Regular ECGs, blood tests for drug levels, and monitoring for side effects are recommended during treatment.
What happens if I take too much Quinidine sulfate?
Taking too much Quinidine sulfate can lead to serious adverse effects, including severe hypotension, cardiac arrhythmias (such as Torsades de Pointes), and central nervous system toxicity like confusion or seizures. If an overdose is suspected, it is critical to seek immediate emergency medical attention. Do not attempt to self-treat or induce vomiting.
Can I drink alcohol while taking Quinidine sulfate?
It is generally advisable to avoid or limit alcohol consumption while taking Quinidine sulfate. Alcohol can exacerbate the central nervous system depressant effects of some medications and may also affect the metabolism of quinidine, potentially altering its effectiveness or increasing the risk of side effects. Always consult your healthcare provider for personalized advice regarding alcohol use with your medication.
Is Quinidine sulfate safe during pregnancy?
Quinidine sulfate is categorized as a Pregnancy Category C medication. This means that animal reproduction studies have shown an adverse effect on the fetus, but there are no adequate and well-controlled studies in humans. Therefore, it should only be used during pregnancy if the potential benefit justifies the potential risk to the fetus. It is essential to consult your doctor to discuss the risks and benefits if you are pregnant or planning to become pregnant.
What is the mechanism of action of quinidine sulfate?
Quinidine sulfate is a class Ia antiarrhythmic agent. It works by blocking fast inward sodium channels during phase 0 of the cardiac action potential, slowing depolarization. It also inhibits potassium channels, prolonging repolarization and the refractory period. This dual action slows conduction velocity and increases the duration of the action potential, reducing the likelihood of abnormal electrical circuits and arrhythmias. (1)
What is the generic name of Quinidine Sulfate?
The generic name is quinidine sulfate. It is sold under brand names including Quinidine Sulfate, Kinidin Durules, Cardioquin, Quinidine Sulphate, Qunil, Quinaglute.
What class of drug is quinidine sulfate?
Quinidine Sulfate is classed as: Class Ia antiarrhythmic.
References
- Quinidine Sulfate for Irregular Heartbeats — Prescribing InformationMedGuideGlobal · United States · accessed 2026-08-07 · source 1
- DEXTROMETHORPHAN HYDROBROMIDE AND QUINIDINE SULPHATE CAPSULE [GOLDEN STATE MEDICAL SUPPLY, INC.] — US prescribing information (DailyMed SPL)U.S. National Library of Medicine (DailyMed) · US · accessed 2026-08-14 · source 2
- Quinidine — patient drug information (MedlinePlus)U.S. National Library of Medicine (MedlinePlus) · US · accessed 2026-08-14 · source 3
- NUEDEXTA — FDA approval record (Drugs@FDA NDA021879)U.S. Food and Drug Administration · US · accessed 2026-08-14 · source 4
- quinidine — RxNorm normalized drug concept (RXCUI 35220)U.S. National Library of Medicine (RxNorm) · US · accessed 2026-08-14 · source 5
Brand names by country
Single-ingredient quinidine sulfate names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.