GENERIC NAME: quinidine

BRAND NAMES: Quinaglute, Quinidex

DRUG CLASS AND MECHANISM: Quinidine is used to correct heart rhythm disturbances and is an antiarrhythmic medication. Three actions are responsible for quinidine's ability to stop heart rhythm disturbances (arrhythmias) and prevent their recurrence. Quinidine decreases the speed of electrical conduction in the heart muscle. It prolongs the electrical phase during which heart muscle cells become electrically stimulated (action potential) and prolongs the recovery period during which the heart muscle cells cannot be stimulated (refractory period).

Quinidine also blocks the normal effect of the vagus nerve on the heart, causing an increase in heart rate. Quinidine reduces the force of contraction of heart muscle cells, and therefore may further impair the pumping efficiency of a failing heart muscle. Quinidine blocks alpha-receptors in peripheral arteries which lowers blood pressure, and can cause excessively low blood pressure when combined with other blood vessel relaxing drugs (vasodilators).

PRESCRIPTION: yes

GENERIC AVAILABLE: yes

PREPARATIONS: Generic quinidine sulfate tablets (200, 300 mg); Quinidex extentabs (300 mg); Quinaglute dura-tabs (324 mg).

STORAGE: Tablets should be stored at room temperature in a tightly closed container.

PRESCRIBED FOR: Quinidine is an antiarrhythmic drug used in the treatment of abnormal heart rhythms, such as:

• Early (premature) atrial and ventricular beats;
• Intermittent rapid rhythms (tachycardias) involving the atria and AV junction as well as extra pathways (bypass tracts) between the atria and ventricles;
• Intermittent atrial fibrillation and flutter;
• Sinus rhythm after conversion from atrial fibrillation or flutter to prevent recurrence; and
• Ventricular tachycardia.

DOSING: Quinidine is administered with food. It is metabolized mainly by the liver with a small amount of kidney excretion. Dosages may need to be lowered in patients with liver or kidney dysfunction.

DRUG INTERACTIONS: Quinidine should not be taken by people who are known to be allergic to it or quinine. Rarely, quinidine causes a low platelet count by stimulating production of an antiplatelet antibody. Quinidine has also been reported to cause diffuse joint aches as well as liver toxicity (hepatitis). Excess quinidine can induce a syndrome called "cinchonism" consisting of various sound and visual disturbances, rashes, and central nervous system changes including headache, confusion, and loss of consciousness. Quinidine can depress heart muscle function, lower blood pressure, and worsen slow heart beats (bradycardia) as well as aggravate heart block. Quinidine can slow the rate of atrial flutter. When quinidine is used for this indication, a second agent such as digoxin is used to slow conduction from the atria to the ventricles. Quinidine is avoided in patients who might be adversely affected by an agent with vagus nerve blocking effects (anticholinergic), such as those with the disease myasthenia gravis .

Quinidine can cause ventricular tachycardia with loss of consciousness which can develop into ventricular fibrillation, resulting in death. Therefore, patients are usually started on quinidine while being monitored in a hospital setting with constant observation of their heart rhythm.

Serum levels of digoxin are raised by quinidine, usually requiring dose reduction of digoxin to prevent toxicity. Quinidine also increases the action of the blood thinner warfarin (Coumadin), requiring a decrease in warfarin dose. Liver metabolism of quinidine is accelerated by phenobarbital, phenytoin (Dilantin), and rifampin (Rifamate), requiring an increase in quinidine dose. Amiodarone (Cordarone), cimetidine (Tagamet), and ketoconazole (Nizoral) increase quinidine levels, requiring a decrease in quinidine dose.

Safety and efficacy of quinidine has not been established in children.

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 diarrhea and nausea which can occur even at low doses. These symptoms cause discontinuation of the drug in 1/4 to 1/3 of patients. Other side effects include vomiting, heartburn, rash, fever, dizziness , and headache.

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