Methotrexate and Sulfamethoxazole Trimethoprim: Drug Interaction Guide

Quick answer: This is a major interaction — avoid combining Methotrexate and Sulfamethoxazole Trimethoprim unless specifically directed by your doctor.

Interaction severity: Major — avoid combination

How Methotrexate interacts with Sulfamethoxazole Trimethoprim

Trimethoprim and methotrexate both inhibit folate pathways, and sulfamethoxazole-trimethoprim may reduce renal tubular secretion of methotrexate. The combination can cause severe bone marrow suppression and mucositis.

What you should do

Avoid the combination whenever possible. If unavoidable, use specialist oversight with close full blood count, renal function and toxicity monitoring.

Key facts

Severity

Major — avoid combination

Mechanism

Trimethoprim and methotrexate both inhibit folate pathways, and sulfamethoxazole-trimethoprim may reduce renal tubular s...

Action

Avoid the combination whenever possible. If unavoidable, use specialist oversight with close full blood count, renal fun...

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 Methotrexate and Sulfamethoxazole Trimethoprim together?

No — this combination should generally be avoided. Avoid the combination whenever possible. If unavoidable, use specialist oversight with close full blood count, renal function and toxicity monitoring.

What is the severity of this interaction?

The interaction between Methotrexate and Sulfamethoxazole Trimethoprim is classified as Major — avoid combination. Trimethoprim and methotrexate both inhibit folate pathways, and sulfamethoxazole-trimethoprim may reduce renal tubular secretion of methotrexate. The combination can cause severe bone marrow suppression and mucositis.

What should I do if I'm prescribed both?

Avoid the combination whenever possible. If unavoidable, use specialist oversight with close full blood count, renal function and toxicity monitoring. Always consult your prescribing clinician — do not stop or change medications without medical guidance.

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