Drug Interaction Report

ADJUST DOSE: Coadministration with inhibitors of P-glycoprotein (P-gp) may increase the plasma concentrations of talazoparib, which has been shown in vitro to be a substrate of the efflux transporter. In a drug-drug interaction study in patients with advanced solid tumors, compared with a single talazoparib dose (0.5 mg), multiple daily doses of the P-gp inhibitor itraconazole (100 mg twice daily) with a single dose of talazoparib (0.5 mg) increased the talazoparib total exposure and peak plasma concentration by 56% and 40%, respectively. In addition, population pharmacokinetic analysis has shown that administration of talazoparib with the P-gp inhibitors amiodarone, carvedilol, clarithromycin, itraconazole, and verapamil resulted in an approximate 45% increase in talazoparib exposure and an increase in the rate of talazoparib dose reduction. In contrast, coadministration with the P-gp inhibitors azithromycin, atorvastatin, diltiazem, felodipine, fluvoxamine, and quercetin increased talazoparib exposure by just 8%.

MANAGEMENT: Concomitant use of talazoparib with amiodarone, carvedilol, clarithromycin, itraconazole, or verapamil should preferably be avoided. If coadministration is required, talazoparib should be initiated at a reduced dosage of 0.75 mg once daily. Patients should be closely monitored for adverse effects such as myelosuppression and myelodysplastic syndrome/acute myeloid leukemia, and further dosage adjustments made or treatment withheld as needed in accordance with the product labeling. After 3 to 5 half-lives following discontinuation of the P-gp inhibitor, the talazoparib dosage may be increased to that used prior to initiation of the P-gp inhibitor.

Grapefruit juice may delay the gastrointestinal absorption of clarithromycin but does not appear to affect the overall extent of absorption or inhibit the metabolism of clarithromycin. The mechanism of interaction is unknown but may be related to competition for intestinal CYP450 3A4 and/or absorptive sites. In an open-label, randomized, crossover study consisting of 12 healthy subjects, coadministration with grapefruit juice increased the time to reach peak plasma concentration (Tmax) of both clarithromycin and 14-hydroxyclarithromycin (the active metabolite) by 80% and 104%, respectively, compared to water. Other pharmacokinetic parameters were not significantly altered. This interaction is unlikely to be of clinical significance.