Can you take erythromycin with methotrexate?
Often, this combination is risky because erythromycin can raise methotrexate levels in the body, which increases the chance of methotrexate side effects (including low blood counts and liver or lung toxicity). This interaction is well known enough that clinicians typically avoid it or use close monitoring if a combination is unavoidable.
What makes the interaction dangerous?
Erythromycin can inhibit drug transport/metabolism pathways that help clear methotrexate. When methotrexate clearance slows, drug levels can build up faster than expected, especially in people who have reduced kidney function or who take higher-dose methotrexate.
What should you do if you were prescribed both?
Check with the prescriber or pharmacist before taking them together. They may recommend:
- switching to a different antibiotic,
- adjusting the methotrexate dose,
- or doing extra lab monitoring (often including complete blood counts and liver/kidney tests).
Do not start, stop, or change methotrexate on your own.
Are there situations where it’s sometimes used?
Sometimes it’s used only when there’s no good alternative, but that usually comes with tighter safety monitoring. The need for monitoring is higher for:
- kidney disease or dehydration,
- older age,
- higher-dose methotrexate (or combined use with other interacting medicines),
- concurrent NSAIDs or other drugs that can also affect methotrexate toxicity risk.
What side effects would suggest methotrexate toxicity?
Get medical attention urgently if you develop signs such as:
- unusual bruising or bleeding, frequent infections, extreme tiredness (possible low blood counts),
- mouth sores or severe sore throat,
- shortness of breath, persistent cough, or fever,
- yellowing of the skin/eyes or dark urine (possible liver injury),
- severe nausea/vomiting or worsening diarrhea.
What alternatives might doctors consider?
Your clinician may choose another antibiotic that does not raise methotrexate levels to treat the infection, depending on the type of infection and your allergy history.
Important check: what methotrexate regimen are you on?
The risk can differ a lot between low-dose methotrexate (common for autoimmune disease) and high-dose methotrexate (common in cancer treatment). Tell your pharmacist/prescriber:
- the dose of methotrexate,
- how often you take it,
- your kidney function history (if you know it),
- and the exact erythromycin product and dose.
If you share your methotrexate dose, why you take it, your kidney function (normal vs impaired), and which erythromycin you have, I can help you think through how to discuss the safest plan with your clinician.