Drug Interaction Report

MONITOR: Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of romidepsin, which is a substrate of the efflux transporter. Although there are no formal drug interaction studies, the interaction may increase the risk of hematologic toxicities such as anemia, leukopenia, and thrombocytopenia as well as electrocardiographic changes such as QT interval prolongation and T-wave and ST-segment changes.

MANAGEMENT: Caution is advised if romidepsin is prescribed in combination with P-gp inhibitors. Pharmacologic response to romidepsin should be monitored more closely whenever a P-gp inhibitor is added to or withdrawn from therapy, and the romidepsin dosage adjusted as necessary. Patients should have complete blood cell counts, electrocardiograms, and serum electrolyte levels performed at baseline and regular intervals as recommended in the product labeling. Patients should be advised to seek medical attention if they experience symptoms that could indicate the occurrence of torsade de pointes such as dizziness, lightheadedness, fainting, palpitation, irregular heart rhythm, shortness of breath, or syncope.

ADJUST DOSE: Smoking tobacco may decrease the steady-state systemic exposure of istradefylline by 38% to 54%.

MANAGEMENT: The possibility of reduced therapeutic effects of istradefylline should be considered in smokers. The manufacturer recommends an istradefylline dosage of 40 mg once daily in patients who smoke 20 or more cigarettes (or the equivalent amount of another tobacco product) per day.