Evaluation of the effect of P‐glycoprotein inhibition and induction on talazoparib disposition in patients with advanced solid tumors

AIMS: In vitro data show that talazoparib is a substrate for P-glycoprotein (P-gp) and breast cancer resistance protein transporters. This open-label, 2-arm, drug-drug interaction Phase 1 study in patients with advanced solid tumours assessed the effect of a P-gp inhibitor (itraconazole) and a P-gp inducer (rifampicin) on the pharmacokinetics of a single dose of talazoparib. The safety and tolerability of a single dose of talazoparib with and without itraconazole or rifampicin were also assessed. METHODS: Thirty-six patients were enrolled (Arm A [itraconazole], n = 19; Arm B [rifampicin], n = 17). Patients in both arms received 2 single oral doses of talazoparib (0.5 mg, Arm A; 1 mg, Arm B) alone and with multiple daily oral doses of itraconazole (Arm A) or rifampicin (Arm B). RESULTS: Coadministration of itraconazole and talazoparib increased talazoparib area under the plasma concentration-time profile from time 0 extrapolated to infinity by ~56% and maximum observed plasma concentration by ~40% relative to talazoparib alone. Coadministration of rifampicin and talazoparib increased talazoparib maximum observed plasma concentration by approximately 37% (geometric mean ratio 136.6% [90% confidence interval 103.2-180.9]); area under the curve was not affected relative to talazoparib alone (geometric mean ratio 102.0% [90% confidence interval 94.0-110.7]). Talazoparib had an overall safety profile consistent with that observed in prior studies in which talazoparib was administered as a single dose. CONCLUSION: Coadministration of itraconazole increased talazoparib plasma exposure compared to talazoparib alone. A reduced talazoparib dose is recommended if coadministration of potent P-gp inhibitors cannot be avoided. Similar exposure was observed when talazoparib was administered alone and with rifampicin suggesting that the effect of rifampicin on talazoparib exposure is limited.