Hypersensitivity to IV Ustekinumab but Tolerance to Subcutaneous Ustekinumab in a Patient With Crohn's Disease.

Ustekinumab is a monoclonal antibody against the p40 subunit of interleukin (IL)-12 and IL-23 and is US Food and Drug Administration (FDA)-approved for plaque psoriasis, moderately to severely active Crohn's disease, and ulcerative colitis. We describe a case of an immediate hypersensitivity reaction to ustekinumab infusion with no reaction to subsequent ustekinumab subcutaneous maintenance therapy. We identify ethylenediaminetetraacetic acid as a unique excipient found in the intravenous formulation compared with the prefilled syringe used for subcutaneous injections, which is likely to account for this observation.