quinidine, Quinidine Gluconate, Quinidine Sulfate (cont.)

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Medical and Pharmacy Editor:

Phenothiazines such as thioridazine (Mellaril), an antipsychotic drug, and tricyclic antidepressants such as amitriptyline (Elavil, Endep) should not be used with quinidine since they can cause cardiac arrhythmias, and their use with quinidine increases the risk of cardiac arrhythmias.

Quinidine increases the action of the blood thinner warfarin (Coumadin), due to synergistic effects and can lead to excessive blood thinning and bleeding. A decrease in warfarin dose usually is required. Blood levels of digoxin (Lanoxin) are raised by quinidine due to a reduction in removal or reduced distribution in the body of digoxin. This can give rise to intoxication with digoxin, and it is important to reduce the dose of digoxin to prevent toxicity.

Removal of quinidine by the liver is accelerated by phenobarbital, phenytoin (Dilantin), and rifampin (Rifamate), requiring an increase in quinidine dose.

With the exact mechanism not known, amiodarone (Cordarone), another type of antiarrhythmic drug, may decrease removal of quinidine by the kidneys or liver giving rise to elevated quinidine blood levels, which may result in life-threatening arrhythmias, including torsades de pointes. It is important, therefore, to decrease quinidine doses when it is given concomitantly with amiodarone.

Cimetidine (Tagamet) increases quinidine levels by decreasing the elimination of quinidine giving rise to elevated quinidine serum levels that may lead to quinidine toxicity.

PREGNANCY: Safety and efficacy of quinidine has not been established in pregnant women.

NURSING MOTHERS: Quinidine can enter breast milk and should be avoided by nursing mothers.

SIDE EFFECTS: The most common side effects are vomiting, heartburn, rash, fever, dizziness, fatigue, weakness and headache. If patients experience irregular heartbeat, chest pain, skin rash, hearing changes (ringing or loss of hearing), vision changes (blurred or light sensitivity) or unusual bleeding or bruising they should call their doctor immediately.

Reference: FDA Prescribing Information

Last Editorial Review: 7/31/2009

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