title: Quinidine-digoxin interaction: effect of quinidine on 86Rb-uptake of human erythrocytes.
abstract: Co-administration of quinidine results in a marked increase in serum digoxin concentration (SDC). The implication of this increase in SDC in regard to an increased digoxin effect on the heart is controversial. The 86Rb-erythrocyte-assay represents a perfect model to study whether quinidine interferes with digoxin at the Na-K-ATPase (the so called glycoside receptor) and thus presumably with the inotropic effect of the glycoside. The inhibitory effect of digoxin (0-150 ng/ml) on the 86Rb-uptake was measured in the absence and presence of quinidine in therapeutic or higher concentrations (0-60 microgram/ml). Addition of quinidine produced no effect on digoxin-induced inhibition of Na-K-ATPase activity. Together with our clinical observations these results strongly suggest that the increased SDC during concomitant quinidine therapy actually reflects an increased digoxin effect on the heart.
mesh_terms: D004077:Digoxin / Q000097:blood / Q000494:pharmacology*; D004347:Drug Interactions; D004912:Erythrocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D009200:Myocardial Contraction / Q000187:drug effects; D011802:Quinidine / Q000494:pharmacology*; D011868:Radioisotopes; D012413:Rubidium; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism
chemical_list: D011868:Radioisotopes; D004077:Digoxin; D000254:Sodium-Potassium-Exchanging ATPase; D011802:Quinidine; D012413:Rubidium