Digitalis-quinidine interaction.

An interaction between quinidine and digoxin is known to occur with toxic concentrations of digoxin in the serum resulting when the two drugs are administered together. The effects can be very dangerous, especially in those patients with advanced and severe cardiac disease. When prescribing quinidine for patients who are taking digoxin, the dose of digoxin should be reduced by half. The patient should be followed carefully, and the electrocardiogram and serum digoxin concentration monitored in order to adjust the digoxin dose.