Quinidine is used to treat certain types of irregular heartbeats. Quinidine is in a class of medications called antiarrhythmic medications. It works by making your heart more resistant to abnormal activity.

Side Effects Of Quinidine

Quinidine may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

  • diarrhea
  • nausea
  • vomiting
  • heartburn
  • fever
  • dizziness
  • lightheadedness
  • headache
  • fatigue
  • weakness
  • rash
  • difficulty sleeping
  • tremor

Some side effects can be serious. If you experience any of the following symptoms, call your doctor immediately:

  • ringing in the ears or loss of hearing
  • vision changes (blurred vision or light sensitivity)
  • confusion
  • unusual bleeding or bruising
  • loss of appetite, nausea, yellow eyes or skin, pain in the upper right area of the stomach, or dark urine

Warnings & Precautions

Before taking quinidine:

  • tell your doctor and pharmacist if you are allergic to quinidine, quinine, or any other drugs.
  • tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, and nutrition supplements you are taking or plan to take. Be sure to mention any of the following: acetazolamide; amiodarone (Nexterone, Pacerone); antidepressants; calcium channel blockers such as diltiazem (Cardizem, Cartia, Diltzac, others), felodipine, nicardipine (Cardene), nifedipine (Adalat, Procardia), nimodipine, or verapamil (Calan, Covera, Verelan, in Tarka); cimetidine (Tagamet HB); codeine products; digoxin (Lanoxin); diuretics (‘water pills’); ketoconazole; medications for mental illness such as haloperidol (Haldol), perphenazine, and thioridazine; methazolamide; mexiletine; phenobarbital; phenytoin (Dilantin, Phenytek); propranolol (Hemangeol, Inderal, Innopran); sodium bicarbonate (Arm and Hammer Baking Soda, in Zegerid OTC); and warfarin (Coumadin, Jantoven). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with quinidine, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
  • tell your doctor if you have heart block (a condition in which electrical signals are not passed normally from the upper chambers of the heart to the lower chambers) or have or have ever had immune thrombocytopenia (ITP; idiopathic thrombocytopenic purpura; an ongoing condition that may cause easy bruising or bleeding due to an abnormally low number of platelets in the blood) or myasthenia gravis (a disorder of the nervous system that causes muscle weakness). Your doctor may tell you not to take quinidine.
  • tell your doctor if you have or have ever had a prolonged QT interval (a condition that increases the risk of developing an irregular heartbeat that may cause fainting or sudden death); a slow heartbeat; low blood levels of calcium, magnesium, or potassium in your blood; or liver or kidney disease.
  • tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while taking quinidine, call your doctor.
  • if you are having surgery, including dental surgery, tell the doctor or dentist that you are taking quinidine.

Quinidine Dosage

Quinidine comes as a tablet (quinidine sulfate) and an extended-release (long-acting) tablet (quinidine gluconate) to take by mouth. Quinidine sulfate tablets are usually is taken every 6 hours. Extended-release quinidine gluconate tablets are usually is taken every 8 to 12 hours. Take quinidine at around the same times every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take quinidine exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

The extended-release tablet may be split in half. Swallow the whole or half tablets whole; do not chew or crush them.

Quinidine helps control your condition but will not cure it. Continue to take quinidine even if you feel well. Do not stop taking quinidine without talking to your doctor.


Keep all appointments with your doctor and the laboratory. Your doctor will need to determine your response to quinidine.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.


All information has been provided courtesy of MedLinePlus from the National Library of Medicine and from the FDA.