RESUMEN
AIMS: There is increasing evidence that erlotinib exposure correlates well with treatment outcome. In this report we present a case of therapeutic drug monitoring of erlotinib in a patient with a gastric ulcer, treated with the proton pump inhibitor pantoprazole. This agent may cause an unwanted, but not always unavoidable, interaction since absorption of erlotinib is pH dependent. METHODS: Erlotinib trough concentrations were monitored in a patient during treatment with orally and intravenously administered pantoprazole. RESULTS: Erlotinib trough concentrations were diminished during high dose intravenously administered pantoprazole, but returned to normal when the dose was reduced and pantoprazole was administered orally. CONCLUSIONS: More studies are needed to assess the dose dependency of the interaction between pantoprazole and erlotinib. Furthermore, we advise to monitor closely erlotinib plasma concentrations and adjust the erlotinib dose accordingly when a clinically relevant interaction is suspected and no proper dosing guidelines are available.