Drug interactions
Methotrexate + Sulfisoxazole
Severity: Major
Methotrexate and Sulfisoxazole: major interaction.
Last updated Sources: US FDA label
For healthcare professionals — reference only. This page is a brief summary, not medical advice and not a substitute for official labeling or clinical judgement. Always verify before prescribing or dispensing.
Summary
Sulfonamides such as sulfisoxazole can raise methotrexate levels and add to antifolate toxicity, risking myelosuppression. This is most relevant at higher methotrexate doses.
What this interaction means in plain words
Methotrexate and Sulfisoxazole can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Why it happens
Sulfonamides displace methotrexate from plasma proteins and reduce its renal tubular secretion.
What to do
Avoid the combination if possible and choose a non-sulfonamide antibiotic. If it must be used, monitor blood counts and renal function closely.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Methotrexate
- Acitretin + Methotrexate Contraindicated
- Adenovirus types 4 and 7 live + Methotrexate Contraindicated
- Influenza virus vaccine quadrivalent intranasal + Methotrexate Contraindicated
- Ketorolac + Methotrexate Contraindicated
- Measles mumps and rubella vaccine live + Methotrexate Contraindicated
- Measles mumps and rubella vaccine + Methotrexate Contraindicated
Frequently asked questions
Can I take Methotrexate with Sulfisoxazole?
MediHelp rates the interaction as major. Methotrexate and Sulfisoxazole can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Sulfonamides such as sulfisoxazole can raise methotrexate levels and add to antifolate toxicity, risking myelosuppression. This is most relevant at higher methotrexate doses.
How serious is the interaction between Methotrexate and Sulfisoxazole?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Avoid the combination if possible and choose a non-sulfonamide antibiotic. If it must be used, monitor blood counts and renal function closely.
What other medicines interact with Methotrexate?
MediHelp also lists interactions of Methotrexate with, for example, Acitretin, Adenovirus types 4 and 7 live, Influenza virus vaccine quadrivalent intranasal. The full list is on the Methotrexate page.
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