Interaction entre Quinidine et Vérapamil

Until further data are obtained, avoid combined therapy of verapamil and quinidine in patients with hypertrophic cardiomyopathy.

Concomitant administration of quinidine [see Drug Interactions ( 7.10 )] preceded the severe hypotension in 3 of the 8 patients (2 of whom developed pulmonary edema).

Quinidine In a small number of patients with hypertrophic cardiomyopathy, concomitant use of verapamil and quinidine resulted in significant hypotension.

There has been a report of increased quinidine levels during verapamil therapy.

The electrophysiological effects of quinidine and verapamil on AV conduction were studied in 8 patients.

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 ).

This hazard may be decreased if partial atrioventricular block is achieved prior to initiation of quinidine therapy, using conduction-reducing drugs such as digitalis, verapamil, diltiazem, or a β-receptor blocking agent.

Hepatic clearance of quinidine is significantly reduced during coadministration of verapamil , with corresponding increases in serum levels and half-life.

For example, when quinidine and verapamil are coadministered in doses that are each well tolerated as monotherapy, hypotension attributable to additive peripheral α-blockade is sometimes reported.

Interactions with other dihydropyridine calcium channel blockers have not been reported, but these agents (including felodipine, nicardipine, and nimodipine ) are all dependent upon P450 IIIA4 for metabolism, so similar interactions with quinidine should be anticipated.