Possible Interaction: Cardiac Glycosides and Quinidine

“Quinidine, the extroisomer of quinine, was first used by Frey in 1918 in he conversion of atrial fibrillation to sinus rhythm, and it as quickly appreciated that quinidine could prolong the T interval and provoke dangerous ventricular arrhythmias, specially in the presence of a cardiac glycoside.”

“Because digoxin toxicity is frequently associated with severe morbidity and mortality, close monitoring of clinical and laboratory signs are mandatory whenever the cardiac glycoside is coadministered with quinidine , verapamil, amiodarone, nifedipine, and indomethacin.”

“Evidence has been obtained that quinidine is capable of decreasing the affinity for digoxin of cardiac glycoside receptor sites on purified Na,K-ATPase and on intact human erythrocyte membranes.”

“A concentration dependent inhibition of the cellular uptake of both cardiac glycosides by quinine and quinidine was found, quinine being a more potent inhibitor than quinidine.”

“It is suggested that quinidine reduces the extrarenal clearance of digoxin at least in part by inhibiting the intestinal secretion of this glycoside.”

“ Quinidine causes a marked increase in plasma digoxin concentration in patients receiving the glycoside.”

“ Quinidine has been shown to alter pharmacokinetics of digoxin by displacing the glycoside from mutual binding sites which are stereospecific with respect to quinidine.”