What is quinidine sulfate used for?

Quinidine sulfate is used to restore normal heart rhythm in people with atrial fibrillation or flutter, and it can also be used to treat certain types of malaria.

Can quinidine sulfate cause hearing problems?

Yes, quinidine can cause 'cinchonism,' which includes symptoms like ringing in the ears (tinnitus), hearing loss, or vertigo.

Is quinidine sulfate safe to take while pregnant?

Quinidine should only be taken during pregnancy if it is clearly necessary, as there are no well-controlled studies on its safety in pregnant women.

What should I do if I experience dizziness or confusion while taking quinidine sulfate?

These could be signs of quinidine toxicity (cinchonism); you should contact your doctor immediately.

Can quinidine sulfate be used in people with heart disease?

It can be used, but there is an increased risk of death in some patients with structural heart disease taking anti-arrhythmic therapies.

Does food affect how quinidine sulfate works?

Taking quinidine sulfate with food may slow down how fast it is absorbed, but it doesn't change the total amount your body takes in.

Who should NOT take quinidine sulfate?

You should not take it if you are allergic to quinidine/quinine, have certain blood disorders from previous use, or rely on a pacemaker without a functional artificial one.

What are the most common side effects of quinidine sulfate?

The most common side effects are stomach-related, such as diarrhea, nausea, vomiting, and heartburn.

Quinidine sulfate dihydrate | CAS 6591-63-5 | ZHNFLHYOFXQIOW

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Anti-arrhythmic (heart rhythm regulator)

Quinidine sulfate is a medication used to treat certain irregular heartbeats (arrhythmias), such as atrial fibrillation or flutter, and has also been used to treat malaria. It works by blocking sodium channels in the heart to help restore a normal rhythm. Because it can increase the risk of death in some patients with heart disease, it is used carefully and often requires close medical monitoring.

How it worksIt works by blocking sodium channels in the heart, which helps control the electrical signals that cause irregular heartbeats.

Brand names:QUINIDEX

Used for

Restoring normal heart rhythm in patients with atrial fibrillation or flutterReducing how often atrial fibrillation or flutter comes backTreating certain types of irregular heartbeats (ventricular arrhythmias)Treating life-threatening malaria (P. falciparum)

Conditions

Atrial fibrillationAtrial flutterVentricular arrhythmiasMalaria

Class

AntiarrhythmicAntimalarialAnti-arrhythmic (heart rhythm regulator)CardiovascularGastrointestinalNeurological

How to take

FormsOral tablets

RoutesOral

Dosage varies based on the condition being treated. For atrial fibrillation, doctors may start with a specific regimen and adjust based on how the heart responds and how the electrical rhythm (QT interval) changes. Always follow your doctor's exact instructions.

For malaria treatment, quinidine sulfate tablets are used as part of a specific regimen that usually includes an injection of Quinidine Gluconate. For heart rhythm issues, treatment should often happen in a setting where medical staff can monitor your heart and provide emergency care if needed.

Key warnings

·There is a risk of increased death in some patients taking anti-arrhythmic drugs for non-life-threatening heart rhythm issues, especially those with structural heart disease.
·Quinidine can cause new or worsened heart rhythm problems (proarrhythmic effects).
·Symptoms like ringing in the ears, hearing loss, or confusion may indicate quinidine toxicity (cinchonism).

Do not use if

·People with a known allergy to quinidine or quinine.
·People who developed a specific blood disorder (thrombocytopenic purpura) during previous treatment with quinidine or quinine.
·People who rely on a pacemaker for their heart rhythm and do not have a functioning artificial pacemaker.
·People with myasthenia gravis who might be harmed by anticholinergic drugs.

Side effects

Common

DiarrheaNauseaVomitingHeartburnLightheadednessHeadacheFatiguePalpitations

Serious

·Cinchonism (symptoms include ringing in the ears, hearing loss, dizziness, blurred vision, confusion, or delirium)
·Increased risk of death in certain heart patients
·Dangerous heart rhythm changes (proarrhythmic effects)
·Liver problems (hepatotoxicity)
·Severe allergic reactions

Seek help if

·Ringing in the ears
·Hearing loss
·Confusion or delirium
·Blurred vision
·Severe dizziness
·Palpitations

Interactions

·Drugs that make urine more alkaline (like sodium bicarbonate or certain diuretics) can decrease how your body gets rid of quinidine.
·Certain medications like amiodarone or cimetidine may increase quinidine levels in your body.
·Drugs that affect liver enzymes (like phenobarbital, phenytoin, or rifampin) may speed up how the body clears quinidine.
·Ketoconazole may increase quinidine levels.
·Propranolol may affect how quinidine is processed by the body.

FoodTaking quinidine with food may slow down how quickly the drug is absorbed, but it does not change the total amount absorbed.

Special populations

PregnancyQuinidine should only be used during pregnancy if clearly needed. There are no well-controlled studies in pregnant women, but some studies show the drug can pass to the baby through the placenta.

BreastfeedingIt is best to avoid using quinidine while breastfeeding if possible. While levels in milk are lower than in the mother's blood, babies may be more sensitive to the drug's toxic effects.

PediatricQuinidine has been used safely for malaria in children, but its safety and effectiveness for treating heart rhythm issues in children have not been established.

GeriatricThe safety and effectiveness of quinidine in elderly patients have not been systematically studied.

Talk to your doctor

Monitor

·Heart rhythm (ECG/QT interval)
·Serum quinidine levels
·Hearing and vision
·Gastrointestinal symptoms

Questions to ask

·Is my heart rhythm stable enough for quinidine sulfate?
·How will my kidney or liver function affect my dose?
·Are my other medications safe to take with quinidine sulfate?
·What signs of toxicity should I watch for?

Pharmacokinetics

OnsetPeak serum levels generally appear about 2 hours after dosing.

BioavailabilityThe absolute bioavailability is about 70%, though it varies between 45% and 100% between patients.

Protein binding80% to 88% in adults and older children; lower in pregnant women and infants.

MetabolismSubject to first-pass metabolism in the liver.

ExcretionRenal elimination is affected by drugs that alkalinize the urine.

Practical

OverdoseAn overdose can cause dangerous heart rhythms and low blood pressure. Symptoms may include vomiting, diarrhea, ringing in the ears, hearing loss, dizziness, blurred vision, confusion, or delirium. Seek emergency medical help immediately if an overdose is suspected.

Ingredients

Allergens

none

Inactive

confectioner’s sugarcorn starchmicrocrystalline cellulosepregelatinized starchzinc stearate

Educational summary derived from FDA labeling, AI-assisted. Not medical advice — consult a healthcare professional. Updated 2026-04-25.