[Interaction of quinidine and digitoxin in the human (author's transl)]

With a daily maintenance dose of 0.1 mg digitoxin a mean steady state digitoxin serum concentration of 17.0 +/- 3.2 ng/ml was measured in 10 male probands. When 750 mg of quinidine bisulphate were administered at the same time digitoxin concentration increased significantly to 22.4 +/- 4.2 ng/ml (P less than 0.0005). The serum half life of digitoxin during quinidine treatment was significantly increased to 10.8 +/- 2.1 days compared to a control group with 7.6 +/- 1.6 days (P less than 0.0025). Protein binding of digitoxin, renal digitoxin excretion and renal digitoxin clearance were equally uninfluenced by quinidine as were endogenous creatinine clearance and sodium and potassium excretion in urine. In two patient with cardiac insufficiency there was likewise a significant increase in digitoxin serum concentration. For clinical application of combined therapy of quinidine and digitoxin the danger of digitalis intoxication seems to be less in comparison to digoxin as increase of digitoxin concentration in serum is lower than of digoxin.