Bexxar in a murine (mouse) monoclonal antibody conjugated to the radioisotope Iodine-131 It's generic name is Tositumomab I-131 Like other radioimmunotherapies Bexxar combines the targeting ability of a monoclonal antibody directed against the CD20 antigen, with the additional power of a radioactive particle to kill nearby cells. This allows it to kill nearby lymphoma cells even when it has not attached to them thus giving greater cell kill than a cold antibody would.
Bexxar uses the Iodine-131 isotope for the radioactive particle. This is both a beta and a gamma radiation emitter. The advantage to the gamma emission is that it can be imaged directly. The disadvantage is that gamma radiation is potentially more harmful and therefore the patient must follow certain restrictions regarding contact with other people for about a week after treatment.
The beta emissions from Bexxar have a path length of about 1mm. In comparison the path length of Zevalin is about 5mm so it might be more effective against larger tumours. But the longer path length also means more normal tissue is likely to be affected.
Iodine-131 is attracted to the thyroid gland, as well as the stomach. Since some of the Iodine-131 is shed from the Tositumomab antibody, it will usually find its way to the thyroid. Therefore all patients receiving Bexxar therapy must take potassium iodide to protect the thyroid gland. Bexxar is administered in two steps.
Bexxar emits gamma radiation in addition to beta radiation. Gamma radiation can escape from the body, therefore special radiation precautions must be taken for about 1-2 weeks after Bexxar therapy.
Scroll down near the bottom of the above link to find the patient release instructions.
The first dose of Bexxar is given with just a small amount of the Iodine-131 radionucleotide attached. This first infusion is called the dosimetric dose. Since Iodine-131 is both a gamma and beta radiation emitter it can be imaged directly, because the imaging cameras detect gamma radiation only.
Approximately 2-4 days after the dosimetric dose, and again at approximately 6-7 days the patient will be scanned to see where the Bexxar is being distributed in the body. (It is the beta radiation that actually does the lymphoma killing)
The therapeutic dose is given between 7-14 days after the dosimetric dose, after calculating the optimum dose based on the previous scans.
Your doctor will discuss the special safety precautions you must follow after Bexxar therapy.
Below are some studies about the use of Bexxar. These studies are focused on using it in novel ways and not on its just approved uses. This is mainly due to the fact that Bexxar (and Zevalin) are under used and in order for them to remain on the market we need to focus on how they may be used best.
Please note the last study in this list. It addresses the extremely important issue of whether or not patients who cannot have Rituxan due to previous severe infusion reactions, can safely have Bexxar. As it turns out it is very safe for these patients, which means they retain a very potent treatment option in the future even though they cannot have Rituxan. This is due to the different type of antibody used.