Iodine-131 tositumomab

The Bexxar therapeutic regimen combined tositumomab, an anti-CD20 murine IgG2a monoclonal antibody, with the same antibody radiolabelled with iodine-131. It was approved by the FDA in 2003 (and in Canada in 2005) for CD20-positive relapsed or refractory low-grade, follicular or transformed non-Hodgkin lymphoma in patients who had progressed during or after rituximab therapy, including rituximab-refractory disease. It was given as a single course only, comprising an unlabelled predose followed by a dosimetric and then a therapeutic dose of 131I-tositumomab, with activity individualised to deliver a specified total-body radiation dose.

Bexxar competed with the similar CD20-targeted radioimmunotherapy ibritumomab tiuxetan (Zevalin, labelled with yttrium-90). Despite comparable efficacy, Bexxar's use declined steadily after a 2006 peak: by 2012 only about 75 US patients received it in a year. GlaxoSmithKline announced in August 2013 that it would discontinue manufacture and sale of the regimen, citing projected declining sales and the availability of alternative therapies; marketing was formally withdrawn on 20 February 2014.

Bexxar is a useful cautionary example in the graph: an approved, effective radiopharmaceutical regimen withdrawn for commercial rather than safety reasons, illustrating how logistics (dosimetry visits, hospital nuclear-medicine capacity, competition from simpler agents) can end a therapy's market life even when clinical data support it.