Medications
Disopyramide - Norpace
Norpace and Norpace CR are 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 Norpace and Norpace CR, their use with lesser arrhythmias is generally not recommended. Treatment of patients with asymptomatic ventricular premature contractions should be avoided.
The adverse reactions which were reported in Norpace 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.
If phenytoin or other hepatic enzyme inducers are taken concurrently with Norpace or Norpace CR, 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 Norpace. Excessive widening of the QRS complex and/or prolongation of the Q-T interval may occur in these situations. In healthy subjects, no significant drug-drug interaction was observed when Norpace was coadministered with either propranolol or diazepam.
Concomitant administration of Norpace and quinidine resulted in slight increases in plasma disopyramide levels and slight decreases in plasma quinidine levels. Norpace does not increase serum digoxin levels.
In the National Heart, Lung and Blood Institute’s Cardiac Arrhythmia Suppression
Trial (CAST), a long-term, multi-center, randomized, double-blind study in patients
with asymptomatic non-life-threatening ventricular arrhythmias who had had a
myocardial infarction more than 6 days but less than 2 years previously, an
excessive mortality or non-fatal cardiac arrest rate (7.7%) was seen in patients
treated with encainide or flecainide compared with that seen in patients assigned to
carefully matched placebo-treated groups (3.0%). The average duration of
treatment with encainide or flecainide in this study was 10 months.
