Drug-drug interaction of fluorinated pyrimidine anticancer agents with phenytoin is well known, but interaction with phenobarbital is limited. We describe a case showing increases in plasma phenobarbital as well as phenytoin concentrations during preoperative S-1 (tegafur/gimeracil/oteracil) and radiation therapy for rectal cancer.
Keywords: S‐1; drug‐drug interaction; phenobarbital; phenytoin; therapeutic drug monitoring.
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