Classification: Radiolabeled Monoclonal Antibody
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".
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:
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.
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:
For more suggestions, read the Neutropenia Tip Sheet.
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.
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.
Read the thrombocytopenia tip sheet for more information.
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.
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.
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.
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.
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.
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: