Overview
DESCRIPTION Disopyramide phosphate, USP is an antiarrhythmic drug available for oral administration in capsules containing 100 mg or 150 mg of disopyramide base, present as the phosphate. The base content of the phosphate salt is 77.6%. The structural formula of disopyramide phosphate, USP is: C 21 H 29 N 3 O•H 3 PO 4 M.W. 437.
Mechanism of Action
CLINICAL PHARMACOLOGY Mechanisms of Action Disopyramide phosphate is a Type 1 antiarrhythmic drug (i.e., similar to procainamide and quinidine). In animal studies, disopyramide phosphate decreases the rate of diastolic depolarization (phase 4) in cells with augmented automaticity, decreases the upstroke velocity (phase 0) and increases the action potential duration of normal cardiac cells, decreases the disparity in refractoriness between infarcted and adjacent normally perfused myocardium, and has no effect on alpha- or beta-adrenergic receptors. Electrophysiology In man, disopyramide phosphate at therapeutic plasma levels shortens the sinus node recovery time, lengthens the effective refractory period of the atrium, and has a minimal effect on the effective refractory period of the AV...
Indications
- INDICATIONS AND USAGE Disopyramide phosphate is indicated for the treatment of documented ventricular arrhythmias such as sustained ventricular tachycardia, that, in the judgment of the physician, are life-threatening. Because of the proarrhythmic effects of disopyramide phosphate, its use with lesser arrhythmias is generally not recommended. Treatment of patients with asymptomatic ventricular premature contractions should be avoided.
Common Doses
- 800 mg
- 600 mg
- 150 mg
- 400 mg
Dosage
DOSAGE AND ADMINISTRATION The dosage of disopyramide phosphate capsules must be individualized for each patient on the basis of response and tolerance. The usual adult dosage of disopyramide phosphate capsules is 400 to 800 mg per day given in divided doses. The recommended dosage for most adults is 600 mg/day given in divided doses (150 mg every 6 hours). For patients whose body weight is less than 110 pounds (50 kg), the recommended dosage is 400 mg/day given in divided doses (100 mg every 6 hours).
Contraindications
- CONTRAINDICATIONS Disopyramide phosphate is contraindicated in the presence of cardiogenic shock, preexisting second- or third-degree AV block (if no pacemaker is present), congenital Q-T prolongation, or known hypersensitivity to the drug.
Side Effects
- ADVERSE REACTIONS The adverse reactions which were reported in disopyramide phosphate clinical trials encompass observations in 1,500 patients, including 90 patients studied for at least 4 years. The most serious adverse reactions are hypotension and congestive heart failure. The most common adverse reactions, which are dose dependent, are associated with the anticholinergic properties of the drug. These may be transitory, but may be persistent or can be severe. Urinary retention is the most serious anticholinergic effect.
Interactions
- Drug Interactions If phenytoin or other hepatic enzyme inducers are taken concurrently with disopyramide phosphate, lower plasma levels of disopyramide may occur. Monitoring of disopyramide plasma levels is recommended in such concurrent use to avoid ineffective therapy. Other antiarrhythmic drugs (e.g., quinidine, procainamide, lidocaine, propranolol) have occasionally been used concurrently with disopyramide phosphate. Excessive widening of the QRS complex and/or prolongation of the Q-T interval may occur in these situations (see WARNINGS ).