This page explains what ATG treatment involves, potential side effects or complications, what to expect from your stay in hospital and about going home afterwards. We hope that this will answer your questions, but please ask your consultant if you would like further information.

What is Anti-Thymocyte Globulin (ATG)?

Anti-Thymocyte Globulin (ATG) is a drug made of antibodies that suppress the immune system. ATG is made by injecting horses with white blood cells from humans, called lymphocytes. By injecting (or immunising) the horses with these human lymphocytes, the horse’s immune system produce antibodies directed against these human lymphocytes. These antibodies are then collected and purified to produce the ATG (ATGAM) medicine. The process of producing ATG does not harm the animals involved.

How does ATG work and how long will it take to have an effect?

Your immune system is your body’s way of fighting off diseases, bacteria and viruses. ATG works by quietening down (suppressing) your immune system for a short period of time. This is done because when your immune system is suppressed, it gives your bone marrow time to heal and make blood cells again. ATG is an effective treatment for aplastic anaemia, and around two out of three patients respond to it. It usually takes about three to six months before ATG starts to work and slowly improves your blood counts. Patients who do not respond may be offered a second course of ATG. Treatment with ATG usually involves staying in hospital for up to three weeks.

Prior to receiving ATG a general assessment of your physical fitness will be undertaken. Often a heart scan (echocardiogram) and pulmonary function tests will form part of this assessment. There is no age limit on receiving ATG, but a decision will be undertaken with your medical team as to whether you are ‘fit’ enough to receive ATG.

How is ATG given?

ATG treatment is started by inserting a central line – a thin plastic tube – into a large vein in your neck or upper part of your chest (a ‘Hickman’ line) or in your upper arm (a ‘PICC’ line). This is used to deliver the medicine. The doctors or nurses or radiographers who insert these types of lines will explain the procedure to you, as well as its risks and benefits. A Hickman or PICC line is used because if you are given ATG through a small drip into the back of your hand or forearm, it can damage and cause inflammation of the small veins in the hand and forearms.

Are there any risks?

Very occasionally (in less than 1% of people) a patient is very allergic to ATG. This could mean they are at risk of sudden collapse (anaphylaxis). So before giving you the first full dose of ATG, you will be given a test dose. This involves giving a small amount of the first dose very slowly over one hour. You will be monitored whilst you are given this test dose to see if you are very allergic to ATG and if no major reactions are seen, the rest of the dose is given at the normal rate. To reduce the risk of a reaction, you will be administered antihistamines and steroids before the ATG. If you have a bad reaction to the test dose, it will be stopped immediately. You will be given drugs to stop the reaction:

• An anti-histamine
• Hydrocortisone (a steroid)
• A dose of adrenaline, if needed

If the reaction is very severe, you will not be treated with the course of ATG.

Are there any alternative treatments?

Other treatments for aplastic anaemia include bone marrow/stem cell transplant and ciclosporin. Although ciclosporin is usually given in combination with ATG, it can also be given without ATG, as a single agent. Another drug is eltrombopag but this is not normally used as a first treatment for aplastic anaemia. Your doctor will discuss these options with you.

What happens after the test dose?

If you have the test dose and do not react to it, you will continue with a course of ATG. Before starting each daily dose, you will have tests to check:

• Your haemoglobin (Hb) level, which is a measure of the number of red cells you have in your blood
• Your white cell levels
• Your platelet levels
• Your blood chemistry
• Your liver and kidney function

If your haemoglobin level and/or platelets are low, you will be given blood and/or platelet transfusions before starting that day’s dose. You will have the full dose of ATG as a slow infusion (released slowly) over 12 – 18 hours through your line.

You usually have the first dose over 18 hours. If it is completed with no major reactions, it may be possible to reduce the time for subsequent doses to around 12 hours each day.

It is not uncommon to have some reactions to ATG. To help reduce the effects of this you will also be given certain other medicines through your line (like antihistamines and steroids to reduce these reactions). You will be given these before starting the ATG and also before each daily dose of the infusion.

What are the common side effects or reactions to ATG?

The most common reactions to ATG are:

• A skin rash
• Rigors (chills and the shakes)
• Fevers
• Weight gain because your body is retaining fluid, also known as ‘oedema’
• Your blood pressure may go up or fall

Cardiac side effects

• Some patients can develop a slow heart rate due to a combination of ATG and steroids, this may require treatment
• Very occasionally patients can develop chest pain during or after ATG, this is why you are assessed for physical fitness prior to receiving ATG, however there remains a small risk which will be explained to you by your doctor.
• ATG may make your platelet counts fall while you are receiving it. This means that it is usually necessary for you to have platelet transfusions on some or most days of the treatment and often in the following weeks.

You will be more at risk of infections, because:

• Your white cell count may already be low and may fall even lower when you have ATG
• ATG suppresses (quietens down) your immune system

This is not a complete list of possible side effects or reactions to ATG, but they are the most common.

What happens after I finish my course of ATG?

After completing your course of ATG you are at a small risk of serum sickness.

Depending on your hospital and the distance you live from it, your doctor may ask you to remain in hospital for another two weeks to be monitored for serum sickness. Alternatively, you may be managed as an outpatient.

If you develop any new fevers or infections, you will need to be readmitted or stay in hospital longer until they have been treated.

To help reduce the immediate side effects of ATG and the later effects of serum sickness, on your first day of ATG you will start having an injection of prednisolone (a type of steroid) once a day into your line. You will later take this in tablet form and the dose will gradually be reduced over a couple of weeks. If you get serum sickness and the effects are not controlled with prednisolone, you may need to receive extra steroids through your central line until the serum sickness settles down.

What other treatment will I be given during my stay in hospital?

While you are having ATG treatment, you will receive more fluids than you are used to. This is because of the extra blood and platelet transfusions and also the fluid that you have through your central line. To help monitor what is going into your body, the nurses, with your help, will keep a ‘fluid balance’ chart. Everything that you drink as well as all fluids put into your central line will be recorded on this chart. You will be weighed daily. If your weight is increasing, or you are retaining more fluid in your body, you maybe given a diuretic (a drug that helps you pass more urine). During your stay in hospital, and even after discharge you will be given antibiotic tablets. These are prophylactic (try to prevent) medicines to protect you from infections. Also, you will be asked to rinse your mouth after meals and last thing at night with a special mouthwash called chlorhexidene.

The nursing staff will keep a close watch by regularly measuring your:

• Temperature
• Pulse
• Respirations (breathing)
• Blood pressure

They will carry out these observations throughout the night too. If your temperature rises above 38°C, you will be given extra antibiotics through your central line.

What happens after I go home?

Treatment with ATG usually takes between three and six months to show an effect on your blood counts, so your red cells, white cells and platelets could remain low during this time. Also, because ATG suppresses your immune system, you may be going home with a lower ability to fight infections. You will therefore need to continue taking any tablets you were given in hospital to help prevent infections.

You will still need to have your blood counts checked regularly and may still need blood and platelet transfusions. This will usually be organised in the day-unit or in the outpatient setting at your local hospital. This is because your haemoglobin and platelet count will not rise for many months. Before you go home, the medical and nursing staff will explain any other special precautions you need to take. 

You can view and download our information booklet here.

Going into hospital for a course of ATG booklet