Posaconazole-digoxin drug-drug interaction mediated by inhibition of P-glycoprotein

Drug-drug interactions between digoxin and the triazole antifungal agents, mediated via various cytochrome P450 isozymes, have been described in the literature. Posaconazole is not extensively metabolized by these isozymes but is both a p-glycoprotein (P-gp) substrate and inhibitor. To our knowledge, there have been no published cases of clinically significant posaconazole-digoxin drug-drug interactions. We report an interaction between posaconazole (300 mg by mouth daily) and digoxin (0.25 mg by mouth daily, Monday through Friday) resulting in atrial fibrillation with slow ventricular response and degenerating into polymorphic ventricular tachycardia.