Allopurinol and Mercaptopurine: Drug Interaction Guide

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

Interaction severity: Major — avoid combination

How Allopurinol interacts with Mercaptopurine

Allopurinol inhibits xanthine oxidase, which is the primary enzyme metabolizing mercaptopurine, leading to markedly elevated mercaptopurine plasma concentrations and risk of severe myelosuppression.

What you should do

Avoid combination if possible. If unavoidable, reduce mercaptopurine dose to 25-33% of the standard dose and monitor full blood count weekly.

Key facts

Severity

Major — avoid combination

Mechanism

Allopurinol inhibits xanthine oxidase, which is the primary enzyme metabolizing mercaptopurine, leading to markedly elev...

Action

Avoid combination if possible. If unavoidable, reduce mercaptopurine dose to 25-33% of the standard dose and monitor ful...

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 Mercaptopurine together?

No — this combination should generally be avoided. Avoid combination if possible. If unavoidable, reduce mercaptopurine dose to 25-33% of the standard dose and monitor full blood count weekly.

What is the severity of this interaction?

The interaction between Allopurinol and Mercaptopurine is classified as Major — avoid combination. Allopurinol inhibits xanthine oxidase, which is the primary enzyme metabolizing mercaptopurine, leading to markedly elevated mercaptopurine plasma concentrations and risk of severe myelosuppression.

What should I do if I'm prescribed both?

Avoid combination if possible. If unavoidable, reduce mercaptopurine dose to 25-33% of the standard dose and monitor full blood count weekly. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

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