Tositumomab (Bexxar®)

Last Modified: September 12, 2012

Pronounced: tos-IT-too-moe-mab
Classification: Radiolabeled Monoclonal Antibody

About Tositumomab

Tositumomab is a type of therapy known as radioimmunotherapy, a combination of a monoclonal antibody and radiation. The monoclonal antibody is directed against an antigen found on all mature B cells, called CD 20. Studies show that as the antibody binds to the B cells, it causes cell death. This is thought to be an immune-mediated response. The antibody also delivers a radioactive isotope (Iodine-131, I-131) to the targeted cells, which emits radiation to kill the cells. This can also kill cells in the surrounding vicinity, a phenomenon known as the "bystander effect".

How to Take Tositumomab

  • The treatment requires preparation prior to the dose and is given in 2 steps. To protect the thyroid gland from the radiation, you will take doses of a potassium solution called SSKI, Lugol's solution, or potassium iodide tablets. You will begin taking this 24 hours before the first dose and continue to take this for at least 14 days following the second dose.
  • On the day of the first dose you will be given premedication with acetaminophen and diphenhydramine to decrease the chance of an allergic reaction.
  • Tositumomab will be given through an IV, over about 1 hour.
  • Following this, tositumomab with I-131 attached is given by IV, over a period of twenty minutes.
  • Over the next week, you will have several scans to determine how the medication is distributed in your body. As long as the distribution is in line with what your physician wants to occur, you will proceed to dose two.
  • You will receive the same premedication to prevent reactions. Then a second dose of tositumomab, followed by tositumomab with I-131 attached is given. This is done between 7-14 days after the original dose.
  • This course of therapy (both steps) is only done once, as no studies have been done to determine if it can be repeated safely.

Possible Side Effects of Tositumomab

There are a number of things you can do to manage the side effects of Tositumomab. Talk to your doctor or nurse about these recommendations. They can help you decide what will work best for you. These are some of the most common side effects:

Reproductive Concerns

Exposure of an unborn child to this medication could cause birth defects, so you should not become pregnant or father a child while on this medication. Effective birth control is necessary during treatment, even if your menstrual cycle stops or you believe your sperm is affected.

Low White Blood Cell Count (Leukopenia or Neutropenia)

White blood cells (WBC) are important for fighting infection. While receiving treatment, your WBC count can drop, putting you at a higher risk of getting an infection. You should let your doctor or nurse know right away if you have a fever (temperature greater than 100.4°), sore throat or cold, shortness of breath, cough, burning with urination, or a sore that doesn't heal.

Tips to preventing infection:

  • Washing hands, both yours and your visitors, is the best way to prevent the spread of infection.
  • Avoid large crowds and people who are sick (i.e.: those who have a cold, fever or cough or live with someone with these symptoms).
  • When working in your yard, wear protective clothing including long pants and gloves.
  • Do not handle pet waste.
  • Keep all cuts or scratches clean.
  • Shower or bath daily and perform frequent mouth care.
  • Do not cut cuticles or ingrown nails. You may wear nail polish, but not fake nails.
  • Ask your doctor or nurse before scheduling dental appointments or procedures.
  • Ask your doctor or nurse before you, or someone you live with, has any vaccinations.

For more suggestions, read the Neutropenia Tip Sheet.

Low Red Blood Cell Count (Anemia)

Your red blood cells are responsible for carrying oxygen to the tissues in your body. When the red cell count is low, you may feel tired or weak. You should let your doctor or nurse know if you experience any shortness of breath, difficulty breathing or pain in your chest. If the count gets too low, you may receive a blood transfusion. Read the anemia tip sheet for more information.

Low Platelet Count (Thrombocytopenia)

Platelets help your blood clot, so when the count is low you are at a higher risk of bleeding. Let your doctor or nurse know if you have any excess bruising or bleeding, including nose bleeds, bleeding gums or blood in your urine or stool. If the count becomes too low, you may receive a transfusion of platelets.

  • Do not use a razor (an electric razor is fine).
  • Avoid contact sports and activities that can result in injury or bleeding.
  • Do not take aspirin (salicylic acid), non-steroidal, anti-inflammatory medications (NSAIDs) such as Motrin®, Aleve®, Advil®, etc. as these can all increase the risk of bleeding. Unless your doctor tells you otherwise, you may take acetaminophen (Tylenol).
  • Do not floss or use toothpicks and use a soft-bristle toothbrush to brush your teeth.

Read the thrombocytopenia tip sheet for more information.

Nausea and/or Vomiting

Take anti-nausea medications as prescribed. If you continue to have nausea or vomiting, notify your doctor or nurse so they can help you manage this side effect. In addition, dietary changes may help. Avoid things that may worsen the symptoms, such as heavy or greasy/fatty, spicy or acidic foods (lemons, tomatoes, oranges). Try antacids, (e.g. milk of magnesia, calcium tablets such as Tums), saltines, or ginger ale to lessen symptoms. Read the Nausea & Vomiting Tip Sheet for more suggestions.

Call your doctor or nurse if you are unable to keep fluids down for more than 12 hours or if you feel lightheaded or dizzy at any time.

Fatigue & Weakness

The most common non-hematologic side effect of this agent is weakness. Some of the weakness may be due to "HAMA" formation. HAMA stands for Human Anti-Mouse Antibodies. This means that the patient has developed antibodies to a small section of the drug that is derived from mice.

While on cancer treatment you may need to adjust your schedule to manage fatigue. Plan times to rest during the day and conserve energy for more important activities. Exercise can help combat fatigue; a simple daily walk with a friend can help. Talk to your healthcare team and see OncoLink’s section on fatigue for helpful tips on dealing with this side effect.

Allergic Reaction

Although uncommon, people may have an allergic reaction to the medication during the infusion. The rate of infusion may be slowed, and the addition of antihistamines and steroids are usually helpful. As mentioned before, you will receive acetaminophen and diphenhydramine prior to each dose to help prevent reactions. If you experience any shortness of breath, cough, itching, rash, lightheadedness or any unusual symptoms, notify your nurse right away.

Secondary Malignancies

There is a small risk of developing leukemia or other type of cancer due to treatment with this medication, which can occur many years later. Discuss this risk with your healthcare provider.

Hypothyroidism Risk

There is a risk of damage to the thyroid gland resulting in hypothyroidism. This is why it is important to take the thyroid protective medications as directed during therapy. You should have your thyroid stimulating hormone (TSH) level checked before treatment and once a year after treatment with tositumomab.

Radiation Exposure

I-131 radiation remains in your system for up to a few weeks and excess not taken up by the thyroid is excreted in urine, stool, saliva and perspiration over the first 1-2 days following treatment. Studies have found the risk to family members to be minimal. However, your healthcare team will give you specific safety guidelines to follow and for how long after treatment to reduce the risk to those around you. These may include:

  • Maintain a distance of 3-6 feet from those around you when possible.
  • Drive alone if possible. Do not sit next to someone in the car for more than a few hours – ride in the backseat on shorter trips.
  • Avoid contact with pregnant women and small children.
  • Do not share food, drinks or eating utensils with others. Do not prepare food for others. Wash your dishes by hand or in the dishwasher – it is best to not use paper products.
  • Sit when urinating to avoid any splashing and wipe dry with toilet tissue after.
  • Shower daily and wash hands frequently.
  • Any trash items that contain your body fluids (menstrual pads, bandages, plastic utensils) should be put in a specific trash bag. Ask your treatment team how to dispose of this trash.
  • Do not sleep in the same bed as someone else. Do not share bed or bath linens and wash these and undergarments separately.
  • Refrain from kissing anyone or having any sexual activity.
  • Pets should not sleep with you to limit their exposure.
  • The radiation you were treated with can set off detectors at airports and other security checkpoints. Talk with your team if you need to travel within this time frame.