Purinethol (6-mercaptopurine, 6-MP)

Purinethol is an effective drug that weakens the immune system. It is often used to prevent a transplanted kidney being rejected. It is at the same time used in the treatment of rheumatoid arthritis, systemic lupus, polymyositis, Crohn’s disease, ulcerative colitis and other autoimmune conditions. It comes as tablets of 50 mg each. It is not a drug like cortisone (prednisolone). It is not habit-forming, and it does not cause drowsiness or impotence.

How it works

How it works is not fully known, but it appears to suppress the immune system, which is working too hard and thereby bringing about Crohn’s disease or ulcerative colitis.

How it is used

The patient should take Purinethol with food, because this drug can irritate the lining of the stomach. It may be taken with milk. One or two tablets should be taken as a single dose a day, as the doctor advises. The drug does not show its effect before three months.

What are the side effects?

If there are side effects such as rash, nausea, vomiting and diarrhoea, these are generally of no consequence.

Some side effects can be very serious: if there is depression of the bone marrow (severe tiredness, fever, sore throat, abnormal bleeding and bruising of the skin, sores on the mouth and lips), damage to the liver (jaundice of the skin and mucous membranes, darkening of the urine), pneumonia caused by the drug (a severe, persistent cough, shortness of breath) or pancreatitis (severe abdominal pain, nausea and vomiting), the doctor should be telephoned at once.

It is thought that certain kinds of cancer, such as Hodgkin’s disease and lymphoma, increase after the use of Purinethol. In a study carried out at the University of Pennsylvania in 2001 this increase in risk was not observed.

Anyone taking the drug should have blood tests at set intervals. Those who are pregnant and those planning to become pregnant soon should not use this drug. Those who have a viral illness, and those taking allopurinol, phenobarbital, phenytoin or rifampicin, should warn their doctor.