Investigation of Potential Drug–Drug Interactions between Peficitinib (ASP015K) and Methotrexate in Patients with Rheumatoid Arthritis

Background Methotrexate is frequently used to treat rheumatoid arthritis. Peficitinib (ASP015K; Smyraf ® ), an oral Janus kinase inhibitor indicated for the treatment of rheumatoid arthritis, may be coadministered with methotrexate. Objective The objective of this study was to investigate potential drug–drug interactions of peficitinib with methotrexate and the short-term safety of coadministration. Patients and Methods This phase I, open-label, single-sequence study included patients with rheumatoid arthritis taking a stable dose of methotrexate. Patients received their prescribed methotrexate dose (Day 1) and then peficitinib (100 mg) twice daily from Day 3 until the morning of Day 9; a second methotrexate dose was coadministered with peficitinib on Day 8. Serial blood samples were collected for methotrexate concentration after dosing on Days 1 (methotrexate alone) and 8 (methotrexate plus peficitinib) and for peficitinib concentration after dosing on Days 7 (peficitinib alone) and 8 (methotrexate plus peficitinib). Pre-dose concentrations of peficitinib were measured (Days 3–8). Results Peficitinib concentrations reached steady state on Day 5. Administration of peficitinib did not result in changes to methotrexate area under the concentration–time curve from time zero to infinity or maximum observed concentration following a methotrexate dose (15–25 mg), and there was no significant effect of methotrexate (15–25 mg) on peficitinib area under the concentration–time curve within a 12-hour dosing interval. There were no new tolerability or safety signals after coadministration of peficitinib and methotrexate. One patient experienced two serious adverse events and withdrew from the study without receiving peficitinib. Conclusions Pharmacokinetic results showed no significant interactions between peficitinib and methotrexate. ClinicalTrials.gov Identifier NCT01754805.