Horse antithymocyte globulin test doses and infusion reactions in adults with aplastic anemia: A multicenter retrospective experience.

Introduction: Horse antithymocyte globulin carries a black box warning for life-threatening anaphylactic reactions, and prescribing information recommends test doses to identify patients at highest risk of this adverse effect. The predictive value of such test doses is not well validated, and practicality of use is unclear.

Methods: This was a planned secondary analysis of a multicenter, retrospective cohort study in adults with severe aplastic anemia being managed with horse antithymocyte globulin as part of their treatment regimen. Qualitative and quantitative descriptions of test doses and infusion reactions are summarized, alongside key institutional administration practices.

Results: Of 49 patients who received intradermal test doses, two experienced positive reactions and went onto receive their full horse antithymocyte globulin course through prolonged infusion time or desensitization. Infusion reaction rate in patients with negative test doses was 61%, corresponding to a negative predictive value of 39%. Premedication, infusion time, and infusion reaction management were similar across institutions.

Conclusion: Horse antithymocyte globulin has a high risk of infusion reactions that must be monitored and managed closely. However, test doses do not consistently predict who will experience an infusion reaction, and their practicality may be limited with current administration practices.