tositumomab

Posted on December 4th, 2008 by

Class: Biologic agent

Generic Name: Tositumomab and Iodine 131 (I131) tositumomab (toe-si-TOO-moe-mab)
Trade Name: Bexxar®

How is this drug used? Tositumomab and I131 is FDA approved for the treatment of patients with CD20 positive, follicular, non-Hodgkin's lymphoma, with and without transformation, whose disease is refractory to rituximab and has relapsed following chemotherapy.  It is important for patients to remember that physicians have the ability to prescribe medication for conditions other than those for which the drug has been approved by the FDA. Patients who have received a prescription of this drug for a condition other than which it is approved may wish to discuss this issue with their physician.
What is the mechanism of action? Tositumomab and I131 tositumomab is a type of agent called a radioimmunotherapeutic. It is comprised of two different portions: a monoclonal antibody designed to recognize a specific target (tositumomab) and a radioactive isotope as a source of radiation (I131). The monoclonal antibody portion has been developed through laboratory processes to bind to B-cells which comprise the majority of cancerous cells in non-Hodgkin's lymphoma. It is thought that this binding action stimulates the immune system to attack the cancer cells. In addition, the radioisotope that is attached to the monoclonal antibody emits radiation, killing the cancer cells in a second manner.

How is tositumomab given (administered)? Tositumomab and I131 tositumomab are administered into a vein (intravenous). The regimen is administered in two steps; the dosimetric step, in which the therapeutic dose is determined, and the therapeutic step, where the patient actually receives the dose for treatment. Each step consists of administration of tositumomab followed by I131 tositumomab.

In the dosimetric step, patients will be administered tositumomab, followed by a small dose of the radioactive material, I131 tositumomab. The radioactive material emits radiation detectable by a special scanner or camera, called a gamma camera. Physicians will take a picture of the radiation to determine the patient’s clearance rate, or how well the radiation is eliminated from the body. Patients will come in two more times, usually within the week of the first visit, for additional gamma ray scans.

The dose of I131 administered in the second step of treatment, called the therapeutic step, is specifically calculated based on the patient’s clearance rate of. The therapeutic dose of tositumomab and I131 tositumomab is administered seven to fourteen days after the first visit.

Treatment with tositumomab and I131 tositumomab may be administered on an outpatient basis. Physicians and nurses who are trained in administration and management of radioactive agents, called nuclear medicine specialists, are in charge of patients treated with this type of drug.  Patients may need to travel to special medical facilities for treatment or larger hospitals may have nuclear medicine facilities within the hospital.  Prior to infusion of the radioactive substance, patients will be given an iodine medication to protect their thyroid from damaging effects of treatment, an agent to help reduce fever (e.g. acetaminophen), and an agent to reduce the risk of allergic-type reactions (e.g. diphenhydramine). The drug for protecting the thyoid will be taken for 14 days after the therapeutic dose is administered.

How are patients monitored? Patients will usually have scheduled meetings with their healthcare provider while they are being treated with tositumomab.  Typically, blood will be drawn to check levels of blood cells and to monitor functions of some organ systems, such as the kidneys or liver.  Patients may also undergo physical examinations, scans or other measures to assess side effects and response to therapy.  Patients may also have levels of their thyroid hormones monitored.

During infusion and up to 2 days following infusion of tositumomab, patients may experience a reaction to the agent with symptoms including fever, chills, sweating, difficulty breathing, nausea or dizziness from low blood pressure. Patients experiencing these symptoms should tell their healthcare provider.

What are the common (occur in 30% or more of patients) side effects of treatment with tositumomab?

• Low levels of white blood cells - increases risk of infection
• Low levels of red blood cells - increases risk of anemia usions
• Low levels of platelets - increases risk of bleeding
• Generalized weakness
• Fever
• Nausea

What are the less common (occur in 10% to 29% of patients) side effects of treatment with tositumomab?

• Infection
• Pain
• Chills
• Headache
• Abdominal pain
• Diarrhea
• Vomiting
• Loss of appetite resulting in severe weight loss
• Muscle or joint aches
• Cough
• Runny nose
• Swollen throat
• Rash
• Itching
• Shortness of breath

This is not a complete list of side effects. Some patients may experience other side effects that are not listed here. Patients may wish to discuss with their physician the other less common side effects of this drug, some of which may be serious.

Some side effects may require medical attention. Other side effects do not require medical attention and may go away during treatment. Patients should check with their physician about any side effects that continue or are bothersome.

What are the possible late side effects of treatment with tositumomab? Patients treated with tositumomab and I131 tositumomab have a slightly increased risk of developing a secondary malignancy. A secondary malignancy is a new and unrelated cancer that occurs in an individual as a result of previous treatment with radiation or chemotherapy.  Patients should ask their physician about the possibility of developing a secondary malignancy as a result of their treatment.  In addition, thyroid hormone levels should be checked annually, as late effects to the thyroid may occur.

What can patients do to help alleviate or prevent discomfort and side effects?

• Pay careful attention to the physician’s instructions and inform the physician of any side effects.
• Maintain adequate rest and nutrition.
• Wear sunscreen and protective clothing and try to minimize sun exposure.
• Drink plenty of fluids. (Patients should ask their physician about the amount of liquid to consume during a day.)

Are there any special precautions patients should be aware of before starting treatment?

• Patients should inform their physician if they are pregnant, breastfeeding or planning a family in the near future. This drug may cause birth defects. It is important to use some kind of birth control while undergoing treatment. Also, patients may want to talk to their physician if they are considering having children in the future, since some drugs may cause fertility problems.
• It is important that patients inform their physician of any pre-existing conditions (chicken pox, heart disease, kidney disease, liver disease, lung disease, etc.) as they may worsen with this drug.
• Patients should inform their physician of any other medication they are taking (whether prescription or over-the-counter, including vitamins, herbs, etc.) as they may interfere with treatment.
• Patients should check with their physician before starting any new drug or nutritional supplement.
• Patients should inform their physician of any known drug or food allergies or any reactions to medications they have experienced in the past.
• Patients will be instructed by their physician as to the radiation precautions they will need to take when they return home, so as not to expose others to radiation.

When should patients notify their physician?

• Fever, chills, runny nose, sore throat, cough
• Signs of infection - redness, swelling, pus, painful urination
• Extreme or prolonged fatigue
• Unexplained bleeding or bruising - nosebleeds, blood in the urine, black or tarry stools
• Persistent nausea, vomiting or diarrhea
• Extreme weight loss
• Shortness of breath, difficulty breathing
• Infusion reactions, including fever, chills, sweating, difficulty breathing, nausea or dizziness, facial swelling, rash
• Chest pain
• Swelling of extremities

What is a package insert?
A package insert is required by the FDA and contains a summary of the essential scientific information needed for the safe and effective use of the drug for healthcare providers and consumers.  A package insert typically includes information regarding specific indications, administration schedules, dosing, side effects, contraindications, results from some clinical trials, chemical structure, pharmacokinetics and metabolism of the specific drug. By carefully reviewing the package insert, you will get the most complete and current information about how to safely use this drug. If you do not have the package insert for the drug you are using, your pharmacist or physician may be able to provide you with a copy.

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Tags: Biological Therapy, Drug Dictionary, T

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