Quinidine sulfate
Pronunciation: Unavailable in research notes.
- Generic name
- quinidine sulfate
- Brand names
- Quinidine Sulfate
- Drug class
- Class Ia antiarrhythmic and antimalarial agent
- Form
- Tablet
- Route
- Oral
- Legal status
- Prescription-only medicine
Availability and supply rules vary by country
Trade names by country:
Australia: · Full directory
What quinidine sulfate is and how it works
Quinidine sulfate is a Class Ia antiarrhythmic and antimalarial agent. It is used for conversion of symptomatic atrial fibrillation or flutter to sinus rhythm, reduction of relapse into atrial fibrillation/flutter, suppression of life-threatening ventricular arrhythmias, and treatment of life-threatening Plasmodium falciparum malaria. (1)
Quinidine carries an increased mortality risk in non-life-threatening arrhythmias; treatment of asymptomatic arrhythmias is generally avoided. It is not first-line for atrial fibrillation and is used only after ventricular rate control has failed to provide satisfactory symptom control. Initiation and dose adjustment must take place in a setting with continuous ECG monitoring and resuscitation facilities.
Mechanism of action: how quinidine sulfate works
Quinidine is a Class Ia antiarrhythmic that prolongs the QTc interval; it also exhibits antimalarial activity against Plasmodium falciparum. (1)
What quinidine sulfate is used for
Conversion of symptomatic atrial fibrillation/flutter
Quinidine may be used to convert symptomatic atrial fibrillation or atrial flutter to sinus rhythm when ventricular rate control has failed to provide satisfactory symptom control. (1)
Reduction of relapse into atrial fibrillation/flutter
Quinidine may be used to reduce the frequency of relapse into atrial fibrillation or atrial flutter. (1)
Suppression of life-threatening ventricular arrhythmias
Quinidine is used to suppress recurrent documented life-threatening ventricular arrhythmias such as sustained ventricular tachycardia when electrophysiologic testing guides therapy. (1)
Life-threatening Plasmodium falciparum malaria
Quinidine sulfate is indicated for the treatment of life-threatening Plasmodium falciparum malaria. (1)
Before taking quinidine sulfate
Do not take / not appropriate for
- Do not take quinidine if you have a known allergy to quinidine or quinine. (all products) (1)
- Do not take quinidine if you have a history of thrombocytopenic purpura during previous quinidine or quinine therapy. (all products) (1)
- Do not take quinidine if your heart rhythm depends on a junctional or idioventricular pacemaker, including complete AV block, unless a functioning artificial pacemaker is in place. (all products) (1)
- Do not take quinidine if you have myasthenia gravis or another condition that may be worsened by an anticholinergic medicine. (all products) (1)
- Do not use quinidine for asymptomatic or non-life-threatening arrhythmias due to increased mortality risk. (all indications) (1)
Tell your clinician about
- Any personal or family history of heart rhythm disorders, including atrial fibrillation, flutter, or ventricular tachycardia.
- Presence of a pacemaker, or any heart block.
- History of thrombocytopenia, hemolytic anemia, or allergic reactions to quinine or quinidine.
- Myasthenia gravis or other conditions that could be worsened by anticholinergic effects.
- Use of other medicines that can affect heart rhythm, especially digoxin, amiodarone, verapamil, or other QT-prolonging drugs.
- Use of blood thinners such as warfarin, or any CYP2D6-substrate medications.
- Liver disease or any signs of liver problems.
- Pregnancy, plans for pregnancy, or breastfeeding status.
- All current prescription and over-the-counter medicines, vitamins, and supplements.
How to take quinidine sulfate
- Quinidine is taken orally as tablets, with the specific dose and schedule determined by the prescriber based on the indication, response, and ECG monitoring.
- Initiation and any dose adjustment must be done in a healthcare setting with continuous ECG monitoring and resuscitation facilities.
- Dose changes and any decision about continuing quinidine are made by the prescriber — contact them before altering how you take it.
- For atrial fibrillation/flutter, pretreatment with digitalis or beta-blockers may be required to control ventricular rate.
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
Contact the prescriber for instructions if a dose is missed. Do not take an extra dose or alter the next dose without advice.
Overdose
If overdose is suspected, seek emergency care immediately. Overdose may cause severe arrhythmias, including torsades de pointes. Treatment involves supportive care, ECG monitoring, and possibly interventions to manage arrhythmias and electrolyte imbalances. Do not self-administer other antiarrhythmics without specialist guidance. (1)
Side effects
Common adverse reactions include diarrhea, upper GI distress, lightheadedness, headache, fatigue, and palpitations. Quinidine can also cause cinchonism, hepatotoxicity, blood disorders, and proarrhythmia. The frequency of effects can vary with the dose and individual patient factors.
Diarrhea
What to notice: Loose, frequent, or watery stools; may begin soon after starting therapy.
What to do: If severe, persistent, or leading to dehydration, contact the prescriber. Do not self-treat with anti-diarrheals without approval. (1)
Upper gastrointestinal distress
What to notice: Nausea, vomiting, stomach pain, or heartburn.
What to do: If bothersome or persistent, inform the prescriber. Do not alter the dose on your own. (1)
Lightheadedness
What to notice: Feeling dizzy or faint, especially when standing.
What to do: Rise slowly from sitting or lying positions. If lightheadedness is persistent or leads to falls, contact the prescriber. (1)
Headache
What to notice: Pain or pressure in the head; may be mild to moderate.
What to do: If headaches become severe or frequent, inform the prescriber. Do not exceed recommended doses of over-the-counter pain relievers without guidance. (1)
Fatigue
What to notice: Unusual tiredness or lack of energy.
What to do: If fatigue is excessive or interferes with daily activities, discuss with the prescriber rather than stopping the medicine yourself. (1)
Palpitations
What to notice: Sensation of rapid, pounding, or irregular heartbeat.
What to do: Report any new or worsening palpitations to the prescriber immediately, as this could indicate a serious arrhythmia. Seek emergency care if accompanied by fainting, chest pain, or severe dizziness. (1)
Angina-like pain
What to notice: Chest pain or discomfort that may feel like heart-related pain.
What to do: Discuss any new or worsening chest pain with the prescriber. Seek emergency care if symptoms suggest a heart attack (e.g., pressure, squeezing, pain radiating to arm/jaw). (1)
Cinchonism
What to notice: Tinnitus (ringing in the ears), reversible high-frequency hearing loss, vertigo, blurred vision, diplopia, photophobia, headache, confusion, or delirium.
What to do: Contact the prescriber promptly for assessment. Cinchonism can occur even at therapeutic levels. (1)
Hepatotoxicity
What to notice: Yellowing of skin or eyes (jaundice), dark urine, severe fatigue, abdominal pain, unexplained nausea.
What to do: Contact the prescriber immediately for evaluation. Liver function testing may be required. (1)
Thrombocytopenia or hemolytic anemia
What to notice: Unexplained bruising, bleeding gums, tiny red dots on skin, dark urine, or sudden pallor/fatigue.
What to do: Contact the prescriber urgently for blood tests. Do not delay reporting these signs. (1)
Proarrhythmia
What to notice: New or worsening palpitations, syncope (fainting), near-fainting, or very rapid heartbeat.
What to do: Contact the prescriber immediately. If you faint or have severe symptoms, seek emergency care. (1)
Serious warnings
Torsades de pointes / proarrhythmia — emergency
Symptoms: Palpitations, syncope, severe dizziness, or sudden loss of consciousness.
Action: Seek emergency care immediately if you experience fainting or severe irregular heartbeat. Do not self-adjust the quinidine dose; a clinician must evaluate and manage the arrhythmia. (1)
Paradoxical rapid ventricular rate in atrial flutter — emergency
Symptoms: Very fast heartbeat (>200 bpm), chest pain, shortness of breath, or fainting.
Action: Seek emergency care immediately. This effect may require immediate medical intervention. (1)
Severe hepatotoxicity — emergency
Symptoms: Yellow skin/eyes, severe abdominal pain, confusion, or easy bruising.
Action: Seek emergency care immediately. Liver dysfunction can be rapid and require urgent management. (1)
Marked sinus node depression — emergency
Symptoms: Severe bradycardia (very slow heart rate), lightheadedness, fatigue, or fainting, especially in patients with sick sinus syndrome.
Action: Seek emergency care if symptoms of slow heart rate are severe or lead to loss of consciousness. (1)
Interactions
| Medicine or test | Effect | Action |
|---|---|---|
| Digoxin | Quinidine can double serum digoxin levels, increasing the risk of digoxin toxicity. | The prescriber typically reduces the digoxin dose and monitors digoxin levels closely. Do not change your digoxin dose yourself. (1) |
| Other QT-prolonging drugs | Additive effect can further prolong the QT interval and increase the risk of torsades de pointes. | Avoid concomitant use. Provide a complete medication list to the prescriber and pharmacist. (1) |
| CYP2D6 substrates | Quinidine inhibits CYP2D6, converting extensive metabolizers to poor metabolizers and increasing exposure of drugs metabolized by CYP2D6. | The prescriber may adjust doses of CYP2D6 substrates. Inform the prescriber of all medicines you take, including antidepressants, antipsychotics, and others. (1) |
| Verapamil | Verapamil reduces quinidine hepatic clearance, leading to increased quinidine levels and half-life. | The prescriber will monitor quinidine levels and ECG; dose adjustment may be needed. (1) |
| Amiodarone and cimetidine | These drugs can raise quinidine serum levels. | The prescriber may need to reduce the quinidine dose and monitor levels. (1) |
| Phenobarbital, phenytoin, and rifampin | These enzyme inducers can accelerate quinidine elimination, potentially lowering serum levels and reducing efficacy. | The prescriber may need to increase the quinidine dose or consider alternative antiarrhythmics. (1) |
| Warfarin | Quinidine potentiates warfarin's anticoagulant action, increasing bleeding risk. | The prescriber will monitor INR closely and adjust warfarin dose as needed. Do not change warfarin dose without guidance. (1) |
Pregnancy, breastfeeding, kidney/liver function, age
Pregnancy
There are no adequate and well-controlled human studies. In limited reports, cord blood levels are about 30% of maternal levels. The decision to use quinidine during pregnancy must be made by a clinician, weighing potential benefits against risks. (1)
Breastfeeding
Quinidine is excreted in human milk at levels slightly below maternal serum levels. The prescribing information advises avoiding administration in lactating women who continue to nurse where possible. The decision to breastfeed while taking quinidine should be made with the clinician, considering the importance of the drug to the mother and the potential risks to the infant. (1)
Patients with myasthenia gravis
Quinidine is contraindicated in patients with myasthenia gravis because its anticholinergic effects can worsen muscle weakness. (1)
Monitoring
Before starting
- Confirm the exact indication and eligibility; quinidine should not be used for asymptomatic or non-life-threatening arrhythmias.
- Obtain baseline ECG and ensure serum potassium, magnesium, and calcium are within normal ranges to limit torsades de pointes risk.
- Assess for known contraindications: allergy to quinidine/quinine, thrombocytopenic purpura history, pacemaker status, myasthenia gravis.
- Review all current medications, especially digoxin, other QT-prolonging drugs, and CYP2D6 substrates.
- Ensure initiation setting has continuous ECG monitoring and resuscitation facilities.
During treatment
- The clinical team monitors the ECG regularly and stops treatment if the QRS duration widens to 130% of the pre-treatment baseline (or beyond 130 ms) or the QTc interval widens to 130% of baseline and exceeds 500 ms.
- Measure serum quinidine levels and adjust doses to maintain therapeutic range (approximately 2–6 mg/L).
- Monitor electrolytes (potassium, magnesium, calcium) and keep them in the normal range.
- Observe for signs of cinchonism, hepatotoxicity, and hematologic disorders (thrombocytopenia, hemolytic anemia).
- Reassess the continued need for quinidine and ensure that the benefit-risk balance remains favorable.
Storage
Storage conditions are not detailed in the research notes. Refer to the product label for specific storage instructions.
Study the drug class: Class I antiarrhythmics
Professional information
Clinician-facing context only. Use the current local prescribing information for complete details.
United States
Indication: Atrial fibrillation/flutter conversion
Dose summary: 400 mg (two 200 mg tablets) every six hours. If conversion does not occur after 4–5 doses, the dose may be cautiously increased under continuous ECG monitoring.
Renal context: No specific renal impairment dose adjustment is provided in the available research notes; use clinical judgement. (1)
United States
Indication: Maintenance / reduction of relapse
Dose summary: Start 200 mg every six hours and cautiously increase as tolerated under ECG guidance.
Renal context: No specific renal impairment dose adjustment is provided in the available research notes; use clinical judgement. (1)
United States
Indication: Suppression of life-threatening ventricular arrhythmias
Dose summary: Regimens similar to those used for atrial fibrillation prophylaxis, guided by electrophysiologic testing.
Renal context: No specific renal impairment dose adjustment is provided in the available research notes; use clinical judgement. (1)
Hepatic guidance
Hepatotoxicity, including granulomatous hepatitis, has been reported. Hepatic impairment may alter drug metabolism; monitor liver function and consider dose adjustment based on clinical response and serum levels. No specific dose adjustment recommendations are provided in the available research notes.
Overdose note
Overdose can cause severe arrhythmias, including torsades de pointes and cardiac arrest. Management includes ECG monitoring, supportive care, maintenance of electrolytes, and possibly pacing or other antiarrhythmic interventions. Contact a poison control center for current guidance. (1)
Frequently asked questions
Why is quinidine not used as a first-line treatment for atrial fibrillation?
Quinidine is associated with an increased risk of mortality in non-life-threatening arrhythmias, and it can cause serious side effects including proarrhythmia. It is generally reserved for patients with symptomatic atrial fibrillation or flutter when ventricular rate control has failed. (1)
What is cinchonism and how is it recognized?
Cinchonism is a collection of symptoms caused by quinidine (and related drugs). It can include tinnitus (ringing in the ears), hearing loss, vertigo, blurred vision, headache, confusion, and even delirium. These symptoms can occur even at therapeutic drug levels and should be reported to the prescriber immediately. (1)
Can I take quinidine if I have a history of thrombocytopenia?
No. Quinidine is contraindicated in patients with a history of thrombocytopenic purpura associated with prior quinidine or quinine therapy. The prescriber should be informed of any such history. (1)
What is the mechanism of action of quinidine sulfate?
Quinidine is a Class Ia antiarrhythmic that prolongs the QTc interval; it also exhibits antimalarial activity against Plasmodium falciparum. (1)
What is the generic name of Quinidine sulfate?
The generic name is quinidine sulfate. It is sold under brand names including Quinidine Sulfate. (1)
What class of drug is quinidine sulfate?
Quinidine sulfate is classed as: Class Ia antiarrhythmic and antimalarial agent. (1)
References
- QUINIDINE SULFATE tablets (Sandoz/Epic Pharma) prescribing informationU.S. Food and Drug Administration via DailyMed · United States · dated 2019-08 · accessed 2026-08-08 · 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.