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Allopurinol and Azathioprine: Drug Interaction Guide

Quick answer: This is a major interaction — avoid combining Allopurinol and Azathioprine unless specifically directed by your doctor.

Interaction severity: Major — avoid combination

How Allopurinol interacts with Azathioprine

Allopurinol inhibits xanthine oxidase, the enzyme responsible for inactivating 6-mercaptopurine (the active metabolite of azathioprine), leading to markedly elevated levels and risk of severe myelosuppression.

What you should do

Avoid combination if possible; if unavoidable, reduce azathioprine dose by 65-75% and monitor full blood count weekly initially.

Key facts

Severity

Major — avoid combination

Mechanism

Allopurinol inhibits xanthine oxidase, the enzyme responsible for inactivating 6-mercaptopurine (the active metabolite o...

Action

Avoid combination if possible; if unavoidable, reduce azathioprine dose by 65-75% and monitor full blood count weekly in...

Important medical disclaimer: This page provides educational information about drug interactions for general reference. It is not a substitute for professional medical advice, diagnosis, or treatment. Always discuss your specific medications with a qualified healthcare provider before starting, stopping, or changing any treatment. About our editorial team.

Frequently asked questions

Can I take Allopurinol and Azathioprine together?

No — this combination should generally be avoided. Avoid combination if possible; if unavoidable, reduce azathioprine dose by 65-75% and monitor full blood count weekly initially.

What is the severity of this interaction?

The interaction between Allopurinol and Azathioprine is classified as Major — avoid combination. Allopurinol inhibits xanthine oxidase, the enzyme responsible for inactivating 6-mercaptopurine (the active metabolite of azathioprine), leading to markedly elevated levels and risk of severe myelosuppression.

What should I do if I'm prescribed both?

Avoid combination if possible; if unavoidable, reduce azathioprine dose by 65-75% and monitor full blood count weekly initially. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

Last reviewed: by iMedic Medical Editorial Team. Our editorial process.