Apparent quinidine-induced digoxin toxicity after withdrawal of pentobarbital: a case of sequential drug interactions.

Accelerated quinidine metabolism was observed in a 94-year-old woman also receiving daily doses of digoxin and pentobarbital sodium. Discontinuation of pentobarbital produced a sharp increase in serum digoxin concentrations coupled with symptoms highly suggestive of digoxin toxicity. Associated with these findings was 3.8-fold increase in quinidine half-life. These data seemed consistent with an interaction between quinidine and digoxin that was precipitated by pentobarbital withdrawal.