Ouabain (OB)

Ouabain is a poisonous cardiac glycoside. It is well understood that the classical mechanism of action of ouabain involves its binding to and inhibition of the plasma membrane Na+/K+-ATPase (sodium pump) especially at the higher concentrations attainable in vitro or with intravenous dosage. Inhibition of the sodium pump and the secondary effect on the handling of calcium ions by sodium calcium exchanger (NCX) is widely believed to underlie the original beneficial effect as an inotropic agent following intravenous use of ouabain; digoxin is a structurally related and more lipophilic cardiac glycoside that largely replaced ouabain for therapy because of its superior oral bioavailability. Digoxin continues to be used therapeutically for many of the same indications in which ouabain was used (including atrial fibrillation and congestive heart failure).