Drug Interaction Report

ADJUST DOSE: Coadministration with potent inhibitors of CYP450 3A4 may significantly increase the plasma concentrations of tofacitinib, which is metabolized by the isoenzyme. In study subjects, administration with the potent CYP450 3A4 inhibitor ketoconazole increased tofacitinib systemic exposure (AUC) by greater than 2-fold compared to administration of tofacitinib alone. Side effects including lymphopenia, neutropenia, anemia, serious infections, and hyperlipidemia may be increased.

MANAGEMENT: The dosage of tofacitinib should be reduced by 50% when used with potent CYP450 3A4 inhibitors. For example, the dose for patients receiving 10 mg twice daily should be reduced to 5 mg twice daily and the dose for patients receiving 5 mg twice daily should be reduced to 5 mg once daily. For patients receiving 11 mg once daily of the extended-release formulation, the dose should be reduced to 5 mg once daily of the immediate-release formulation. The dose for patients receiving 3.2 mg twice daily should be reduced to 3.2 mg once daily and the dose for patients receiving 4 mg twice daily should be reduced to 4 mg once daily.

ADJUST DOSING INTERVAL: Administration of atazanavir with food enhances oral bioavailability and reduces pharmacokinetic variability. According to the manufacturer, administration with a light meal increased the peak plasma concentration (Cmax) and area under the concentration-time curve (AUC) of a single 400 mg dose of atazanavir by 57% and 70%, respectively, relative to the fasting state. Administration with a high-fat meal resulted in a mean increase of 35% in atazanavir AUC and no change in Cmax compared to fasting. The coefficient of variation of AUC and Cmax decreased by approximately one-half when given with either a light or high-fat meal compared to the fasting state.

MANAGEMENT: To ensure maximal oral absorption, atazanavir should be administered with or immediately after a meal.

MONITOR: Grapefruit juice may increase the plasma concentrations of tofacitinib. The proposed mechanism is inhibition of CYP450 3A4-mediated first-pass metabolism in the gut wall by certain compounds present in grapefruits. The extent and clinical significance are unknown. Moreover, pharmacokinetic alterations associated with interactions involving grapefruit juice are often subject to a high degree of interpatient variability.

MANAGEMENT: Until more information is available, some authorities recommend avoiding consumption of grapefruit juice during tofacitinib therapy (Canada). Patients receiving tofacitinib therapy who ingest grapefruits or grapefruit juice should be monitored for adverse effects and undue fluctuations in plasma drug levels.