DISOPYRAMIDE (SUBGROUP 1A)
The effects of disopyramide are very similar to those of procain-amide and quinidine. Its cardiac antimuscarinic effects are even more marked than those of quinidine. Therefore, a drug that slows AV conduction should be administered with disopyramide when treating atrial flutter or fibrillation.
Toxic concentrations of disopyramide can precipitate all of the electrophysiologic disturbances described under quinidine. As a result of its negative inotropic effect, disopyramide may precipi-tate heart failure de novo or in patients with preexisting depression of left ventricular function. Because of this effect, disopyramide is not used as a first-line antiarrhythmic agent in the USA. It should not be used in patients with heart failure.
Disopyramideâ€™s atropine-like activity accounts for most of its symptomatic adverse effects: urinary retention (most often, but not exclusively, in male patients with prostatic hyperplasia), dry mouth, blurred vision, constipation, and worsening of preexisting glaucoma. These effects may require discontinuation of the drug.
Pharmacokinetics & Dosage
In the USA, disopyramide is only available for oral use. The typi-cal oral dosage of disopyramide is 150 mg three times a day, but up to 1 g/d has been used. In patients with renal impairment, dos-age must be reduced. Because of the danger of precipitating heart failure, loading doses are not recommended.
Although disopyramide has been shown to be effective in a variety of supraventricular arrhythmias, in the USA it is approved only for the treatment of ventricular arrhythmias.