Faculty Bibliography

RATIONALE: Natalizumab is a monoclonal antibody (mAb) indicated for treatment of multiple sclerosis. Natalizumab has special attributes which must be addressed when planning rapid desensitization for immediate hypersensitivity reactions (HSR.) Immediate HSRs during rapid desensitization are common, with consequent need to hold the infusion, treat the HSR, and possibly maintain a slower infusion rate. Complete infusion could require more than 8 hours, however, per FDA approved instructions, each bag of natalizumab solution must be infused within 8 hours of preparation or be discarded. Natalizumab is only supplied as 300 mg singledose vials. One published 3-bag, 12-step rapid desensitization protocol wastes approximately 10% of the drug, by discarding most solution in the first 2 bags. Accordingly, one must open another vial of natalizumab, costing approximately $3,000, or the patient will only receive approximately 90% of the typical intended dose. METHODS: Report of two patients with history of immediate HSR to natalizumab, and adaptation of a 3-bag, 12-step, rapid desensitization protocol as follows: Bag #1-0.6 mg in 50ml; Bag #2-6 mg in 50ml; Bag #3 and Bag #4-each 146.7 mg in 122.25ml. Bag #4 was not prepared until Bag #2 was mostly infused. Bags #2, #3 and #4 were infused completely. RESULTS: 99.8% of the intended dose was infused, without immediate HSR. CONCLUSIONS: With adaptation of a published protocol, rapid desensitization to natalizumab 300 mg is possible, utilizing only one single-dose vial, and with minimal chance of exceeding the FDA-approved eight hour infusion window from the time of preparation of each bag