Purinethol
(Mercaptopurine)

What Purinethol is and what it is used for

Mercaptopurine tablets contain the active substance called 6-mercaptopurine. 6-mercaptopurine belongs to a group of medicines called cytotoxics (also called chemotherapy) and works by reducing the number of new blood cells your body makes. Mercaptopurine is used to treat cancer of the blood (leukaemia) in adults, adolescents and children.

How to take Purinethol

Mercaptopurine should only be prescribed to you by a specialist doctor who is experienced in treating cancers of the blood.
• When you take Mercaptopurine, your doctor will take regular blood tests. This is to check the number and type of cells in your blood, and to ensure your liver is working correctly
• Your doctor may also ask for other blood and urine tests to monitor how your kidneys are working and to measure uric acid levels. Uric acid is a natural substance made in your body and levels of uric acid can rise while you are taking Mercaptopurine. High levels of uric acid may damage your kidneys
• Your doctor may sometimes change your dose of Mercaptopurine as a result of these tests. Always take Mercaptopurine exactly as your doctor or pharmacist has told you. Check with your doctor or pharmacist if you are not sure. It is important to take your medicine at the right times. The label on your pack will tell you how many tablets to take and how often to take them. If the label does not say or if you are not sure, ask your doctor, nurse or pharmacist. The usual dose for adults and children is 2.5 mg per kilogram of your body weight each day (or alternatively 50 to 75 mg per m2 of your body surface area each day). Your doctor will calculate and adjust your dose based on your body weight, results of your blood tests, whether or not you are taking other chemotherapy medicines and your kidney and liver function.
• Swallow your tablets whole. Do not chew the tablets. The tablets should not be broken or crushed. If you or your caregiver does handle broken tablets, wash the hands immediately. You can take your medicine with food or on an empty stomach but the choice of method should be consistent from day to day. You should take your medicine at least 1 hour before or 2 hours after having milk or dairy products. If you take more Mercaptopurine than you should If you take more Mercaptopurine than you should, tell your doctor immediately or go to a hospital straight away. Take the medicine pack with you. If you forget to take Mercaptopurine Tell your doctor. Do not take a double dose to make up for a forgotten dose. If you stop taking Mercaptopurine If you stop taking Mercaptopurine, tell your doctor immediately. If you have any further questions on the use of this medicine, ask your doctor, nurse or pharmacist

Possible side effects

Like all medicines, this medicine can cause side effects, although not everybody gets them. If you get any of the following side effects, talk to your specialist doctor or go to hospital immediately:
• An allergic reaction with swelling of the face and sometimes mouth and throat (this is a very rare side effect).
• An allergic reaction with joint pain, skin rashes, high temperature (fever) (this is a rare side effect).
• Yellowing of the skin and whites of the eyes. If you get such symptoms, you should stop taking Mercaptopurine.
• Any signs of fever or infection (sore throat, sore mouth or urinary problems) or any unexplained bruising or bleeding. Treatment with Mercaptopurine affects your bone marrow and will cause a reduction in your white blood cells and platelets (this is a very common side effect). Talk to your doctor if you have any of the following side effects, which may also happen with this medicine:

Common (may affect up to 1 in 10 people)
• Nausea (you feel sick) or vomiting (being sick)
• Low red blood cell count (anaemia)

Uncommon (may affect up to 1 in 100 people)
• Loss of appetite

Rare (may affect up to 1 in 1,000 people)
• Mouth ulcers
• Inflammation of the pancreas (pancreatitis); symptoms may include abdominal pain or feeling or being sick
• Damage to your liver (hepatic necrosis)
• Hair loss
• Various types of cancers including blood, lymph and skin cancers

Very rare (may affect up to 1 in 10,000 people)
• Blood cancer
• Cancer of the spleen and liver (in patients with a condition called Inflammatory Bowel Disease)
• Ulcers in the intestines; symptoms may include abdominal pain and bleeding
• Low sperm count in men

Not known (frequency cannot be estimated from the available data)
• Increased sensitivity to sunlight and UV light Additional side effects in children Low blood sugar levels (sweating more than usual, nausea, dizziness, confusion, etc.) have been reported in some children receiving Mercaptopurine; however, most of the children were under the age of six years old and had a low body weight.

Reporting of side effects If you get any side effects, talk to your doctor, nurse or pharmacist. This includes any possible side effects not listed in this leaflet. You can also report side effects directly via the Yellow Card Scheme at: www.mhra.gov.uk/yellowcard By reporting side effects you can help provide more information on the safety of this medicine.

How to Store Purinethol

Keep this medicine out of the sight and reach of children.
• Do not use this medicine after the expiry date which is stated on the pack after ‘Exp’.
• Do not store your Mercaptopurine tablets above 25°C. Keep the bottle tightly closed.
• If your doctor tells you to stop taking the tablets, it is important to return any which are left over to your pharmacist, who will destroy them according to disposal of dangerous substance guidelines. Only keep the tablets if your doctor tells you to.