Iodine 131 tositumomab (BEXXAR)

Understanding cancer research trials

When a drug is being developed it has to go through various stages of research, called clinical trials or studies. These are intended to establish a safe dosage, the side effects the drug may cause and which cancers it may be used to treat. The trials also find out how effective the drug is, and whether it is better than the existing treatments or has extra benefit when given with these drugs.

At this stage BEXXAR is available only to a small number of people in the UK, usually those taking part in clinical trials. In certain circumstances it may also be given to individual patients who have been selected by their doctor as suitable (this is called a named patient basis).

Many drugs that are thought to be promising may be found not to be as good as existing treatments, or to have side effects that outweigh any benefits. For this reason, doctors and other medical staff carry out frequent and careful checks on the progress of each patient who is having one of these developmental drugs. If you are taking a developmental drug your doctor will explain all about the drug, the procedures being used, and how you will be looked after while you are taking it. If at any time you have concerns you should ask your doctor or nurse for information and advice.

BEXXAR

BEXXAR is a new type of cancer treatment that involves a group of drugs called monoclonal antibodies. At the moment it is used only in clinical trials to treat a type of B-cell non-Hodgkin’s lymphoma (NHL) that has come back after previous treatment.

What is a monoclonal antibody?

Monoclonal antibodies recognise certain proteins that are found on the surface of some cancer cells. They are used to try to destroy the cancer cells, while causing little harm to normal cells. The monoclonal antibody recognises the protein on the surface of the cancer cell and locks on to it (like a key in a lock). Some monoclonal antibodies can then trigger the body’s immune system to attack the cancer cells and can also cause the cells to destroy themselves. Sometimes monoclonal antibodies, such as BEXXAR, have a cancer drug or radioactive substance attached to them. They can be used in this way to deliver treatment directly to the cancer cell: this is known as targeted therapy.

How does BEXXAR work?

BEXXAR has a radioactive substance called iodine131 attached to it. The monoclonal antibody in BEXXAR, tositumomab, targets a protein found on the surface of the B-cells. The radioactive iodine delivers radiation directly to these cells. This destroys the lymphoma B-cells. Unfortunately it may also affect some normal cells.

How is it given?

BEXXAR is given as a drip (infusion) into the vein, through a fine tube (cannula) inserted into the vein. It is usually given in the nuclear medicine department of your hospital. You will usually need to make four visits over one to two weeks. The first three visits are needed to decide how much radioactivity you will be given and the fourth will actually be the treatment.

Before you start treatment and for two weeks after you are given the treatment dose of BEXXAR, you will need to take a daily iodine supplement. This is taken either as tablets or as liquid drops and helps to protect the thyroid gland from the radioactive iodine.

On the first day of treatment you will be given two separate drips. Before these drips you will be given paracetamol and an antihistamine to help reduce any side effects that may occur. The first drip is an infusion of the monoclonal antibody without any radioactive iodine which is given to you over an hour. This is given to ensure that when you have the second infusion, which contains the radioactivity, it will be evenly spread throughout your body.

The second drip contains the monoclonal antibody with a small amount of radioactive iodine131. This small dose of radioactivity is given to see how the radiation is spread around the body and to help the doctors to decide exactly how much radioactive iodine to give you. Soon after this second infusion you will have the first of three body scans. This takes between 15–30 minutes and shows how much radioactivity is still in the body and where it is.

On the second visit (day 2, 3 or 4) you will have another body scan to see whether there is any radioactivity left in the body.

The third visit on day 6 or 7 involves another body scan. After this the doctors can calculate exactly how much radioactivity to add to the monoclonal antibody to ensure that you get the best possible dose.

The fourth visit (between days 7 and 14) is when you actually have the treatment dose of BEXXAR. You will receive two drips into your cannula, the first one of just the monoclonal antibody, over an hour, and the second containing the dose of radioactive antibody, given over 20 minutes.

After the fourth visit you will need to stay in hospital for a few days because of the possibility of unnecessary radiation exposure to other people. The risk to other people is small and lasts for up to a week until the radiation has been got rid of from your body through your sweat and urine. Certain restrictions will be needed during this time.

You will probably be looked after in a room of your own or with someone else having similar treatment. Lead screens will be placed at either side of your bed to absorb any radiation that is given out. Visiting times will be restricted and pregnant women and children will not be allowed to visit. However, you should feel well and can bring books and magazines into your room, watch TV or listen to the radio to help pass the time.

CancerBACUP’s general information on radiotherapy explains more about treatment with a radioactive substance.

Possible side effects

The known side effects of BEXXAR are not usually severe. However, as it is still a relatively new drug it is too early to know all about the possible side effects. The following appear to be the most common.

Flu-like symptoms These may include fever and chills, headaches, itching and joint and muscle aches. These effects may occur a few hours after the drug is given but do not usually last for more than a day or two.

Temporary reduction in production of blood cells by the bone marrow This can result in a lowering of the number of white cells (which fight infection) in your blood making you more prone to infection. It can also result in bruising or bleeding if your platelets (cells which clot the blood) are reduced, or anaemia if your red cells are low. Your doctor or nurse will advise you about this and any precautions you should take. The blood cells usually recover in three to four weeks.

Allergic reactions  The drug does not usually cause many problems. However, it is possible to have a slight allergic reaction to the monoclonal antibody in BEXXAR. Signs of this include skin rashes and itching, a feeling of swelling in the tongue or throat, irritation of the nasal passages, wheezing, a cough and breathlessness.

You will be monitored closely during your treatment, but tell the nurse or doctor if you have any of these symptoms. To reduce the chance of developing an allergic reaction certain drugs (anti-histamines) can be given before the drip. The drip can be slowed down or stopped until the reaction is over.

Other side effects include weakness and nausea (feeling sick). Your doctor can prescribe anti-sickness drugs to help reduce this.

References

This section has been compiled using information from a number of reliable sources including:

  • Oxford Textbook of Oncology (2nd edition). Souhami et al. Oxford University Press, 2002.
  • Treatment of Cancer (4th edition). Price and Sikora. Arnold, 2002.

For further references, please see the general bibliography.

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Iodine 131 tositumomab (BEXXAR)

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