Rituximab Hypersensitivity: Evaluation, Desensitization, and Potential Mechanisms.

Background: Rituximab (Rituxan) hypersensitivity (RITS) can be severe and limits the ability to further administer the treatment. Understanding its pattern and desensitization may permit administration in difficult cases.

Objective: Analyze RITS patient characteristics, hypersensitivity pattern, and desensitization outcomes to optimize management.

Methods: Twenty-five patients with RITS were referred to the Allergy/Immunology Unit at Massachusetts General Hospital over 5 1/2 years. Their clinical reaction patterns were analyzed. Drug desensitizations were performed using 3 related continuous intravenous protocols that were chosen on the basis of clinical history, skin test reactivity, and the patient's previous desensitization outcomes.

Results: Of the 25 referred patients, 23 had lymphoma of various types. The 25 patients underwent 170 continuous intravenous desensitizations based on 3 related protocols, with most based on the intermediate protocol. All but 2 desensitizations were completed successfully. Overall 24% of the desensitizations were complicated by hypersensitivity reactions. Two patients with serum sickness and a patient with mast cell disorder were also successfully managed. The average hypersensitivity reaction grade was 3.0 (2-4) before desensitization and 0.41 with desensitization. Skin tests were performed in 18 patients, with 5 patients positive initially and 2 more converted from negative to positive. Skin test status was not helpful for risk stratification for hypersensitivity reactions. Tryptase level was elevated during 21% of desensitizations with reactions but rare among asymptomatic desensitizations.

Conclusions: Nearly all patients with severe sensitivity to rituximab can be successfully desensitized. IgE-mediated mechanism and mast cell degranulation, in addition to cytokine release syndrome and tumor lysis syndrome, may contribute to a significant portion of hypersensitivity reactions among patients with RITS.