Brand Name - Quinidine Sulfate

  • Type of Drug: Antiarrhythmic.
  • Prescribed for: Abnormal heart rhythms

Quinidine General Information

Derived from the bark of the cinchona tree (which gives us Quinine), this drug works by affecting the flow of potassium into and out of cells of the myocardium (heart muscle). This function helps it to affect the flow of nervous impulses throughout the heart muscle. Its basic action is to slow down the pulse, which allows control mechanisms in the heart to take over and keep the heart beating at a normal, even rate.

The 3 kinds of Quinidine provide different amounts of active drug, so they cannot be interchanged without your doctor making dosage adjustments. Quinidine Sulfate provides the most active drug.

Some of the different brands come in sustained-release form so that fewer pills are required throughout the day.

Quinidine Cautions and Warnings

Do not take Quinidine if you are allergic to it, Quinine, or a related drug. Quinidine sensitivity may be masked if you have asthma, muscle weakness, or an infection when you start taking the medicine.

Liver toxicity related to Quinidine sensitivity is rare but has occurred. Unexplained fever or liver inflammation may be an indication of this effect; People with kidney or liver disease should take this medicine with caution; lower doses may be necessary.

Like other antiarrhythmic drugs, Quinidine can cause its own abnormal heart rhythms. If this happens, you will be told to stop taking the drug and may be hospitalized for further evaluation.

People taking Quinidine for long periods may experience sudden fainting and/or an abnormal heart rhythm. These may end on their own or respond to medical treatment. Occasionally, these episodes may be fatal.

Quinidine Possible Side Effects

  • Most common: nausea, vomiting, abdominal pain, diarrhea, and appetite loss. These may be accompanied by fever.
  • Less common: Quinidine may cause unusual heart rhythms, but such effects are generally found by your doctor during routine examination or electrocardiogram. It may also cause irritation of the esophagus, affect components of the blood system, and can cause headache, dizziness, feelings of apprehension or excitement, confusion, delirium, muscle aches or joint pains, ringing or buzzing in the ears, mild hearing loss, blurred vision, changes in color perception, sensitivity to bright light, double vision, difficulty seeing at night, flushing of the skin, itching, sensitivity to the sun, cramps, an unusual urge to defecate or urinate, and cold sweat.
  • Rare: allergic reactions to Quinidine can include asthma; swelling of the face, hands, and feet; respiratory collapse; and liver problems.

High doses of Quinidine can cause rash, hearing loss, dizziness, ringing in the ears, headache, nausea, or disturbed vision. This group of symptoms, called cinchonism, is usually related to taking a large amount of Quinidine (but may appear after a single dose of the medicine) and is not necessarily a toxic reaction. Report any sign of cinchonism to your doctor immediately. Do not stop taking this drug unless instructed to do so by your doctor.

Quinidine Drug Interactions

• Quinidine increases the effect of Warfarin and other oral anticoagulants (blood thinners). The anticoagulant dose may have to be adjusted.
• Quinidine may increase the effects of Metoprolol, Procainamide, Propafenone, Propranolol and other beta blockers; Benztropine, Oxybutynin, Atropine, Trihexyphenidyl, and other anticholinergic drugs; and tricyclic antidepressants.
• The effect of Quinidine may be decreased by the following medicines: Phenobarbital or other barbiturates, Phenytoin or other hydantoins. Nifedipine, Rifampin, Sucralfate, and cholinergic drugs (such as Bethanechol).
• The effect (and toxicity) of Quinidine may be increased by taking Amiodarone, some antacids, Cimetidine, anything that decreases urine acid levels, and Verapamil.
• Quinidine can dramatically increase the amount of Digoxin in the blood, causing possible Digoxin toxicity. This combination should be monitored closely by your doctor.
• The combination of Disopyramide and Quinidine can result in increased Disopyramide levels and possible drug side effects and/or reduced Quinidine activity.
• Avoid over-the-counter cough, cold, allergy, or diet preparations. These medications may contain drugs that will stimulate your heart and can be dangerous while you are taking Quinidine. Ask your pharmacist if you have any questions about the contents of a particular cough, cold, or allergy remedy.

Quinidine Usual Dose

Extremely variable, depending on your disease and response. Most doses are 600 to 1200 mg a day.


Most doses are 600 to 1800 mg a day.

Quinidine Overdosage

Overdose produces depressed mental function, including lethargy, decreased breathing, seizures, and coma. Other symptoms are abdominal pain and diarrhea, abnormal heart rhythms, and symptoms of cinchonism (see Possible Side Effects). The victim should be taken to a hospital emergency room. ALWAYS bring the medicine bottle with you.

Quinidine Special Information

Call your doctor if you develop ringing or buzzing in the ears, hearing or visual disturbances, dizziness, headache, nausea, skin rash, difficulty breathing, or any intolerable side effect (see Possible Side Effects).

Do not crush or chew the sustained-release products. Some side effects of Quinidine may lead to oral discomfort (dry mouth), cavities, periodontal disease, and oral Candida infections. See your dentist regularly while taking this drug.

If you forget to take a dose of Quinidine, and you remember within about 2 hours of your regular time, take it right away. If you do hot remember until later, skip the forgotten dose and go back to your regular schedule. Do not take a double dose.

Special Populations

This drug passes into the fetal blood circulation and may cause birth defects or interfere with your baby’s development. Check with your doctor before taking it if you are, or might be, pregnant.
Quinidine passes into breast milk but is considered acceptable for use while breast-feeding. Consult your doctor.

Older adults may be more sensitive to the effects of this medicine because of the likelihood of decreased kidney function. Follow your doctor’s directions, and report any side effects at once.