Supplementary Material for: Association between Dipeptidyl Peptidase-4 Inhibitor Prescription and Erythropoiesis-Stimulating Agent Hyporesponsiveness in Hemodialysis Patients with Diabetes Mellitus

Introduction: Dipeptidyl peptidase-4 (DPP-4) has been hypothesized to improve responsiveness to erythropoiesis-stimulating agent (ESA). We aimed to describe the trend in DPP-4 inhibitor prescription patterns and assess the association between DPP-4 inhibitor prescription and ESA hyporesponsiveness (eHypo) in Japanese hemodialysis (HD) patients with diabetes mellitus (DM). Methods: We analyzed data from the Japan Dialysis Outcomes and Practice Patterns Study phase 4–6 (2009–2017) on patients with DM who underwent HD thrice per week for at least 4 months. The primary exposure of interest was having a DPP-4 inhibitor prescription. The primary analysis outcomes were a binary indicator of eHypo (mean hemoglobin <10 and mean ESA dose >6,000 units/week over 4 months) and the natural log-transformed ESA resistance index (ERI). We used conditional logistic regression to compare within-patient changes in eHypo before and after initial DPP-4 inhibitor prescription. We used linear generalized estimating equation models to compare continuous ERI outcomes while accounting for within-patient repeated measurements with an exchangeable correlation structure. Results: There was a monotonic increase in DPP-4 inhibitor prescription according to study year up to 20% in 2017. Moreover, 12.8% of patients with a DPP-4 inhibitor prescription were ESA hyporesponsive before the initial DPP-4 inhibitor prescription. After DPP-4 inhibitor prescription, the odds of eHypo and mean log-ERI remained unchanged in the whole cohort of our study. The interaction analysis of DPP-4 inhibitor and sideropenia showed that DPP-4 inhibitors attenuated eHypo in the patients without iron deficiency. Conclusion: Our findings indicate a recent increase in DPP-4 inhibitor prescription among Japanese HD patients with DM. DPP-4 inhibitors could improve ERI in patients undergoing HD without iron deficiency.