Azathioprine

What it is

Azathioprine is a purine antimetabolite: it is converted in the body to compounds that interfere with DNA synthesis in dividing lymphocytes, damping the immune response. Its effect develops gradually over weeks. It is used for autoimmune inflammation and for immunosuppression, and it is prescription-only.

Used for

• Autoimmune inflammation
• Immunosuppression

What to know while taking it

It is taken with food to reduce nausea. Because it suppresses the bone marrow, white cells and platelets are checked regularly throughout treatment, not only at the start; it can also injure the liver, so ALT and AST are checked. Allopurinol blocks the enzyme that breaks the drug down and can push its levels sharply higher, so the combination is never made casually. Immune suppression raises the risk of infection, and long-term use raises skin cancer risk, which is why strong sun is avoided and sun protection is advised.

When to see a doctor

Fever, sore throat, mouth ulcers or any infection that will not settle, along with unusual bruising, bleeding or marked fatigue, mean see a doctor without delay. New or changing skin lesions, and yellowing of the skin or eyes, also need assessment.

Worth knowing

• Raises infection risk
• Avoid strong sun
• Blood counts need regular checks

Markers to watch

• White blood cells
• Platelets
• ALT
• AST