Ofatumumab (Arzerra) | Cancer Research UK
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What ofatumumab is

Ofatumumab (pronounced off-ah-chew-moo-mab) is a type of monoclonal antibody. Monoclonal antibodies are a type of biological therapy. Ofatumumab is also known by its brand name Arzerra. It is a treatment for chronic lymphocytic leukaemia.

You may also have it in research trials for other types of cancer.


How ofatumumab works

Monoclonal antibodies are copies of a single antibody. They recognise and find specific proteins on the outside of cancer cells.

Ofatumumab targets part of a protein called CD20 on the surface of the chronic lymphocytic leukaemic cells. The ofatumumab sticks to all the CD20 proteins it finds. Then the cells of the immune system pick out the marked cells and kill them.


How you have ofatumumab

You have ofatumumab through a drip into a vein (infusion) through a pump. Between 30 minutes and 2 hours before you have each treatment you have an injection of corticosteroids. You will also have paracetamol and an antihistamine (either as tablets or into your bloodstream). These reduce the chance of having an allergic reaction to ofatumumab.

Your first treatment is a small test dose and takes around 6 hours. If this goes well the second treatment is the full dose and again takes around 6 hours. If this treatment also goes well and you don’t have any problems you may be able to have further treatments over less than 6 hours.

You usually have the treatment once a week for 8 weeks. Then you have a break with no treatment for 4 or 5 weeks. You then have treatment once every 4 weeks for 4 months.


Tests during treatment

You have blood tests before starting treatment and regularly during your treatment. The tests check your levels of blood cells. They also check how well your liver and kidneys are working.


About side effects

We've listed the side effects associated with ofatumumab below. You can use the links to find out more about each side effect. Where there is no link, please go to our cancer drug side effects section or use the search box at the top of the page.

You may have a few of the side effects. They may be mild or more severe. A side effect may get better or worse through your course of treatment. Or more side effects may develop as the course goes on. This depends on

  • How many times you've had the drug before
  • Your general health
  • The amount of the drug you have (the dose)
  • Other drugs you are having

The side effects may be different if you are having ofatumumab with other drugs.

Tell your doctor or nurse straight away if any of the side effects get severe.


Common side effects

More than 10 in every 100 people have one or more of the side effects listed below.

  • An increased risk of getting an infection from a drop in white blood cells – it is harder to fight infections and you can become very ill. You may have headaches, aching muscles, a cough, breathlessness, a sore throat, pain passing urine, or you may feel cold and shivery. If you have a severe infection this can be life threatening. Contact your treatment centre straight away if you have any of these effects or if your temperature goes above 38°C
  • Tiredness and breathlessness due to a drop in red blood cells (anaemia) – you may need a blood transfusion
  • Bruising more easily due to a drop in platelets – you may have nosebleeds, bleeding gums after brushing your teeth, or lots of tiny red spots or bruises on your arms or legs (known as petechia)
  • An allergic reaction while you have the treatment, causing a skin rash, high temperature (fever), chills, shivering (rigors), a headache and feeling sick – in trials 4 out of 10 people had a reaction during the first treatment and around 3 out of 10 with the second treatment. Rarely, people have a more severe reaction with wheezing, an itchy rash and a drop in blood pressure. Your nurse will stop or slow your drip if you have a reaction
  • Tiredness and weakness (fatigue) affects about 1 in 10 people during and after treatment – most people find their energy levels are back to normal within 6 months to a year
  • A rash, which may be itchy
  • Loss of fertility – you may not be able to become pregnant or father a child after treatment with this drug. Talk to your doctor before starting treatment if you think you may want to have a baby in the future. Men may be able to store sperm before starting treatment

Occasional side effects

Between 1 and 10 in every 100 people have one or more of these effects.

  • A faster heart rate
  • Diarrhoea – drink plenty of fluids and tell your doctor or nurse if it becomes severe or continues for more than 3 days
  • Feeling sick – this is usually well controlled with anti sickness medicines
  • Back pain
  • Shingles or cold sores
  • A blockage in the bowel – let your doctor or nurse know straight away if you have sudden abdominal pain, sickness, or abdominal cramps

Rare side effects

Fewer than 1 in 100 people have these effects.

  • A group of symptoms including headaches, seizures (fits), changes in eye sight, excessive sleepiness, changes in behaviour, and possibly high blood pressure — doctors call this group of symptoms Reversible Posterior Leucoencephalopathy Syndrome (RPLS) – tell your doctor or nurse straight away if you have any of these effects
  • High uric acid levels in the blood due to the breakdown of tumour cells (tumour lysis syndrome) – you will have regular blood tests to check your uric acid levels and may have a tablet called allopurinol to take. Drinking plenty of fluids helps to flush out the extra uric acid
  • A change in blood pressure
  • Muscle spasms

Important points to remember

Talk to your doctor, pharmacist or nurse about all your side effects so they can help you manage them. They can give you advice or reassure you. Your nurse will give you a contact number to ring if you have any questions or problems. If in doubt, call them.

Other medicines

Tell your doctor about any other medicines you are taking, including vitamins, herbal supplements and over the counter remedies. Some drugs can react together.

Pregnancy and contraception

This drug may harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment with this drug and for a year afterwards. Talk to your doctor or nurse about effective contraception before starting treatment.


Do not breastfeed during this treatment or for a year afterwards because the drug may come through in the breast milk.

Hepatitis B and ofatumumab

You will have a blood test to check for hepatitis B before you start treatment. Hepatitis B is a viral infection that can cause inflammation (swelling) of the liver. Ofatumumab can make hepatitis B infection active again. Your doctor may treat you with an anti viral treatment to prevent this. 

Tell your doctor if you have had hepatitis in the past.

Sodium and ofatumumab

Ofatumumab contains sodium. You will need to take account of this if you are on a controlled sodium diet.



You should not have immunisations with live vaccines while you are having chemotherapy or for at least 6 months afterwards. In the UK, these include rubella, mumps, measles (usually given together as MMR), BCG, yellow fever and Zostavax (shingles vaccine).

You can have other vaccines, but they may not give you as much protection as usual until your immune system has fully recovered from your chemotherapy. It is safe to have the flu vaccine.

It is safe for you to be in contact with other people who've had live vaccines as injections. There can be problems with vaccines you take by mouth (oral vaccines), but not many people in the UK have these now. So there is usually no problem in being with any baby or child who has recently had any vaccination in the UK. You might need to make sure that you aren't in contact with anyone who has had oral polio, cholera or typhoid vaccination recently, particularly if you live abroad.


Related information


More information about ofatumumab

This page does not list all the very rare side effects of this treatment that are very unlikely to affect you. For further information look at the Electronic Medicines Compendium website at www.medicines.org.uk.

If you have a side effect not mentioned here that you think may be due to this treatment you can report it to the Medicines Health and Regulatory Authority (MHRA) at www.mhra.gov.uk.

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Updated: 24 January 2014