A monoclonal antibody that is used in the treatment of certain types of non-Hodgkin lymphoma. When tositumomab and iodine I 131 tositumomab (a form of tositumomab that has been chemically changed by adding radioactive iodine) are given together, the combination is called the Bexxar regimen. Also called Bexxar regimen, iodine I 131 tositumomab, and tositumomab and iodine I 131 tositumomab.