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.
(Arch Intern Med 139:363-365, 1979)
Chapron DJ, Mumford D, Pitegoff GI. Apparent Quinidine-Induced Digoxin Toxicity After Withdrawal of PentobarbitalA Case of Sequential Drug Interactions. Arch Intern Med. 1979;139(3):363–365. doi:10.1001/archinte.1979.03630400077027