# Iodine-131 tositumomab

Source: https://nuclide.cc/drugs/i-131-tositumomab/  
Nuclide record `i-131-tositumomab` (Agent). Data CC BY-NC 4.0, attribute "Data from Nuclide (nuclide.cc)"; commercial use needs a licence.

## TL;DR

A cancer-targeting antibody carrying a radioactive form of iodine was used, as a single course, to treat a type of blood cancer called non-Hodgkin lymphoma. The manufacturer stopped selling it in 2014 because too few patients were using it.

## Summary

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of the regimen, citing projected declining sales and the availability of alternative therapies; marketing was formally withdrawn on 20 February 2014.

Bexxar is a useful cautionary example in the graph: an approved, effective radiopharmaceutical regimen withdrawn for commercial rather than safety reasons, illustrating how logistics (dosimetry visits, hospital nuclear-medicine capacity, competition from simpler agents)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.

## Fields

- Kind: Agent
- Status: withdrawn
- Last checked: 2026-09-22
- Also known as: Bexxar; tositumomab and I-131 tositumomab
- Tags: radioimmunotherapy; lymphoma; withdrawn; beta and gamma emitter
- Brand: Bexxar
- Modality: radioimmunotherapy
- Mechanism: An unlabelled anti-CD20 murine monoclonal antibody (tositumomab) dosing step to saturate normal B-cell sinks, followed by the same antibody labelled with iodine-131, which delivers combined beta and gamma radiation directly to CD20-expressing lymphoma cells as well as an antibody-dependent immune effect.
- Approvals: US 2003: CD20-positive relapsed or refractory, low-grade, follicular, or transformed non-Hodgkin lymphoma progressing during or after rituximab therapy; CA 2005: Same indication as the US approval

## Sources

- GSK: announcement of discontinuation, 6 August 2013: https://pipelinereview.com/gsk-to-discontinue-manufacture-and-sale-of-the-bexxar-therapeutic-regimen-tositumomab-and-iodine-i-131-tositumomab/
- JAMA Internal Medicine: Withdrawal of drugs for commercial reasons - tositumomab, 2014: https://static1.squarespace.com/static/55550f38e4b0884d8d80118e/t/5565d1aae4b0660ba5b932e2/1432736170326/2014+-+Nov+-+JAMA+IM+-+Withdrawal+of+Drugs+for+Commercial+Reasons+-+Tositumomab.pdf
- The rise and fall of iodine-131 tositumomab: Bexxar's story: https://openmedscience.com/the-rise-and-fall-of-iodine-131-tositumomab-bexxars-story/

## Connected records

- drugs: [Ibritumomab tiuxetan](https://nuclide.cc/drugs/ibritumomab-tiuxetan/), [Rituximab](https://nuclide.cc/drugs/rituximab/)
- isotopes: [Iodine-131](https://nuclide.cc/isotopes/i-131/), [Yttrium-90](https://nuclide.cc/isotopes/y-90/)
- indications: [Follicular lymphoma](https://nuclide.cc/indications/follicular-lymphoma/)
- technologies: [Radio-antibody & radio-ADC](https://nuclide.cc/technologies/radioimmunotherapy/)
- targets: [CD20](https://nuclide.cc/targets/cd20/)

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