Disopyramide and Quinidine interaction

Considering the known proarrhythmic properties of Norpace or Norpace CR and the lack of evidence of improved survival for any antiarrhythmic drug in patients without life-threatening arrhythmias, the use of Norpace or Norpace CR as well as other antiarrhythmic agents should be reserved for patients with life-threatening ventricular arrhythmias.

As with other Type 1A antiarrhythmics, disopyramide phosphate has been associated with torsade de pointes.

Patients who have evidenced prolongation of the Q-T interval in response to quinidine may be at particular risk.

Concomitant administration of Norpace and quinidine resulted in slight increases in plasma disopyramide levels and slight decreases in plasma quinidine levels.

Q-T Prolongation As with other Type 1 antiarrhythmic drugs, prolongation of the Q-T interval (corrected) and worsening of the arrhythmia, including ventricular tachycardia and ventricular fibrillation, may occur.

Quinidine is also contraindicated in patients who, like those with myasthenia gravis, might be adversely affected by an anticholinergic agent.

Proarrhythmic effects Like many other drugs (including all other Class Ia antiarrhythmics), quinidine prolongs the QT c interval, and this can lead to torsades de pointes , a life-threatening ventricular arrhythmia (see OVERDOSAGE ).

Altered pharmacodynamics of other drugs: Quinidine's anticholinergic, vasodilating, and negative inotropic actions may be additive to those of other drugs with these effects, and antagonistic to those of drugs with cholinergic, vasoconstricting, and positive inotropic effects.