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BACKGROUND: Pembrolizumab and nivolumab are PD-1–blocking antibodies that are FDAapproved for a variety of malignancies. Previously, only 1 fixed dosing schedule was approved for these agents, with nivolumab dosed at 240 mg intravenously (IV) every 2 weeks and pembrolizumab dosed at 200 mg IV every 3 weeks. Recently, the FDA approved an alternate dosing schedule for nivolumab dosed at 480 mg IV every 4 weeks and pembrolizumab dosed at 400 mg IV every 6 weeks following the results of pharmacokinetic simulation models that showed a similar risk-benefit profile based on a relatively small sample size. OBJECTIVE: To compare the incidence of immune-related adverse events (irAEs) and infusion reactions of different FDA-approved dosing regimens for nivolumab and pembrolizumab. METHODS: This single-center, retrospective chart review included 171 adults with cancer who received at least 2 doses of nivolumab or pembrolizumab at either dosing schedule for any diagnosis of cancer at Duke University Health System between January 1, 2018, and June 30, 2021. The primary end point was the incidence of any-grade irAEs occurring in each of the 4 study groups (nivolumab 240 mg IV every 2 weeks, nivolumab 480 mg IV every 4 weeks, pembrolizumab 200 mg IV every 3 weeks, and pembrolizumab 400 mg IV every 6 weeks) within 6 months of treatment initiation. RESULTS: The incidence rates of any-grade irAEs were 40% for the patients who received nivolumab 240 mg IV every 2 weeks and 46% for the patients who received nivolumab 480 mg IV every 4 weeks. The rates of any-grade irAEs were 34% in the patients who received pembrolizumab 200 mg IV every 3 weeks and 47.6% in those who received pembrolizumab 400 mg IV every 6 weeks. Although the number of patients with irAEs was higher in the groups that received nivolumab 480 mg IV every 4 weeks or pembrolizumab 400 mg IV every 6 weeks, the incidence of irAEs was not significantly different between the group that received nivolumab 240 mg IV every 2 weeks versus nivolumab 480 mg IV every 4 weeks (P=.54, chi-square) and the group that received pembrolizumab 200 mg IV every 3 weeks versus pembrolizumab 400 mg IV every 6 weeks (P=.28, chi-square). The patients who received nivolumab 480 mg IV every 4 weeks had a higher incidence of infusion reactions than those who received nivolumab 240 mg IV every 2 weeks (10% vs 4%, respectively). Patients who received pembrolizumab 200 mg IV every 3 weeks had a higher incidence of infusion reactions than those who received pembrolizumab 400 mg IV every 6 weeks (6% vs 0%, respectively). CONCLUSION: The incidence of irAEs was not significantly different among patients receiving nivolumab or pembrolizumab at either dosing schedules. The incidence of infusion reactions was higher in the groups that received nivolumab 480 mg IV every 4 weeks or pembrolizumab 200 mg IV every 3 weeks than in the groups that received nivolumab 240 mg IV every 2 weeks or pembrolizumab 400 mg IV every 6 weeks. Further studies are warranted to validate these results. [ABSTRACT FROM AUTHOR]