Effect of Fluconazole and Itraconazole on the Pharmacokinetics of Erdafitinib in Healthy Adults: A Randomized, Open-Label, Drug–Drug Interaction Study

Background and Objectives Erdafitinib, an oral selective pan-fibroblast growth factor receptor (FGFR) kinase inhibitor, is primarily metabolized by cytochrome P450 (CYP) 2C9 and 3A4. The aim of this phase 1 study was to assess the pharmacokinetics and safety of erdafitinib in healthy participants when coadministered with fluconazole (moderate CYP2C9 and CYP3A inhibitor), and itraconazole (a strong CYP3A4 and P-glycoprotein inhibitor). The effect of CYP2C9 genotype variants (*1/*1, *1/*2, *1/*3) on the pharmacokinetics of erdafitinib was also investigated. Methods In this open-label, parallel-group, single-center study, eligible healthy adults were randomized by CYP2C9 genotype to receive Treatment A (single oral dose of erdafitinib 4 mg) on day 1, Treatment B (fluconazole 400 mg/day orally) on days 1–11, or Treatment C (itraconazole 200 mg/day orally) on days 1–11. Healthy adults randomized to Treatment B and C received a single oral 4-mg dose of erdafitinib on day 5. The pharmacokinetic parameters, including mean maximum plasma concentration ( C max ), area under the curve (AUC) from time 0 to 168 h (AUC 168h ), AUC from time 0 to the last quantifiable concentration (AUC last ), and AUC from time 0 to infinity (AUC ∞ ) were calculated from individual plasma concentration–time data using standard non-compartmental methods. Results Coadministration of erdafitinib with fluconazole increased C max of erdafitinib by approximately 21%, AUC 168h by 38%, AUC last by 49%, and AUC ∞ by 48% while coadministration with itraconazole resulted in no change in erdafitinib C max and increased AUC 168h by 20%, AUC last by 33% and AUC ∞ by 34%. Erdafitinib exposure was comparable between participants with CYP2C9 *1/*2 or *1/*3 and with wild-type CYP2C9 genotype. The ratio of total amount of erdafitinib excreted in the urine (inhibited to non-inhibited) was 1.09, the ratio of total amount of excreted metabolite M6 was 1.21, and the ratio of the metabolite to parent ratio in the urine was 1.11, when coadministration of erdafitinib with itraconazole was compared with single-dose erdafitinib. Treatment-emergent adverse events (TEAEs) were generally Grade 1 or 2 in severity; the most commonly reported TEAE was headache. No safety concerns were identified with single-dose erdafitinib when administered alone and in combination with fluconazole or itraconazole in healthy adults. Conclusion Coadministration of fluconazole or itraconazole or other moderate/strong CYP2C9 or CYP3A4 inhibitors may increase exposure to erdafitinib in healthy adults and thus may warrant erdafitinib dose reduction or use of alternative concomitant medications with no or minimal CYP2C9 or CYP3A4 inhibition potential. Trial Registration ClinicalTrials.gov identifier number: NCT03135106.