Enzyme induction: rifampin-disopyramide interaction.

A 62-year-old woman with a history of supraventricular tachycardia, paroxysmal atrial tachycardia, and premature ventricular contractions was admitted with palpitations and anxiety. Previous therapy with antiarrhythmics had resulted in intolerable adverse effects or no effect on the arrhythmia. She had been taking rifampin prior to admission for acid-fast bacilli. Disopyramide was started on admission for supraventricular tachycardia. Subtherapeutic disopyramide blood concentrations were noted with concomitant administration of rifampin and disopyramide at normal doses. This case report demonstrates a possible drug interaction between these two drugs and the importance of careful monitoring. It was found that it takes three to five days after rifampin is discontinued before the enzyme induction of disopyramide disappears and disopyramide concentrations return to normal.