Drug Interaction Report

Furosemide Injection and Methotrexate: Interaction Details

A pharmacist-reviewed analysis of the Furosemide Injection and Methotrexate interaction: the documented clinical effects, severity rating, onset, mechanism, and management considerations, with cited references throughout.

AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature

Furosemide Injection

Disal Furoscix Furoscix® Lasix Lasix® Salix - substance
+

Methotrexate

Jylamvo Otrexup Rasuvo Reditrex Rheumatrex® Trexall Trexall® Xatmep
Dr. Brian Staiger, PharmD, BCPS
Medically reviewed by
Dr. Brian Staiger, PharmD, BCPS
Updated Aug 8, 2026
Editorial policy · Data sources
LinkedIn
Interaction severity
Major
Potentially serious — often needs a change or close monitoring.
How we grade severity & evidence

Severity levels

  • Contraindicated: These should generally not be used together.
  • Major: Potentially serious — often needs a change or close monitoring.
  • Moderate: Can be significant — usually manageable with monitoring.
  • Minor: Usually limited clinical impact.

Evidence grades

  • Established: Well documented — supported by controlled studies or strong clinical data.
  • Probable: Good supporting evidence, though not definitively proven.
  • Suspected: Some evidence suggests this interaction, but it is not well established.
  • Possible: Limited or conflicting evidence; the interaction may occur.
  • Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.

Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.

Of 241 documented Furosemide Injection interactions, 195 are rated major — including this one.
Worried about symptoms right now? Contact your pharmacist or prescriber, or call Poison Control at 1-800-222-1222 (US). Call 911 for an emergency.
Onset
unspecified
Evidence
theoretical
Severity
Major

What happens

Increased methotrexate exposure, an increased risk of methotrexate-related toxicity, altered (increased/reduced) furosemide exposure, an increased risk of furosemide-related toxicity and reduced efficacy of furosemide

Interaction Deep Dive

Concomitant use of furosemide with methotrexate may reduce the effect of furosemide. Conversely, furosemide may reduce renal elimination of other drugs that undergo tubular secretion (methotrexate). High-dose treatment of furosemide may elevate methotrexate exposure and may potentiate the toxicity of methotrexate. High-dose treatment of methotrexate may increase furosemide exposure and may potentiate the toxicity of furosemide. Monitor for enhanced toxicity of furosemide. Also, monitor for the serum levels of furosemide/methotrexate and adjust the dose if needed21.

Why it happens (mechanism)

Reduced renal elimination of methotrexate; reduced renal elimination of furosemide

Common questions

Can I take Furosemide Injection and Methotrexate together?

Increased methotrexate exposure, an increased risk of methotrexate-related toxicity, altered (increased/reduced) furosemide exposure, an increased risk of furosemide-related toxicity and reduced efficacy of furosemide Always confirm with your pharmacist or prescriber before making any change.

How serious is the Furosemide Injection and Methotrexate interaction?

It is rated major. Potentially serious — often needs a change or close monitoring.

How quickly could this interaction happen?

The documented onset is "unspecified". The timing of this interaction is not well characterized.

How strong is the evidence for this interaction?

The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.

From our Q&A

Real reader questions about these medications, each personally answered by our pharmacist:

Questions for your pharmacist

  • Does my dose of Furosemide Injection or Methotrexate need adjusting while I take them together?
  • What symptoms should prompt me to call you or my prescriber right away?
  • Does the timing of my doses matter for this combination?
  • Is there a safer alternative to one of these medications for me?

References (2)

  1. Product Information: LASIX® ONYU subcutaneous injection, furosemide subcutaneous injection. SQ Innovation, Inc (per manufacturer), Burlington, MA, 2025. DailyMed
  2. Product Information: FUROSCIX(R) subcutaneous injection, furosemide subcutaneous injection. scPharmaceuticals Inc (per FDA), Burlington, MA, 2025. DailyMed
Was this write-up helpful?
Furosemide Injection

Keep reading about Furosemide Injection

All Furosemide Injection interactions (241) Furosemide Injection drug information
Also serious with: Methenamine Desmopressin Vonoprazan Dapagliflozin
Methotrexate

Keep reading about Methotrexate

All Methotrexate interactions (420) Methotrexate drug information
Also serious with: Rubella Virus Vaccine, Live Smallpox Monkeypox Vaccine Varicella Virus Vaccine, Live Typhoid Vaccine
Beyond drug–drug

These medications also interact with supplements

Prescription drugs aren't the whole picture — herbal and dietary supplements can interact with them too. From the evidence-graded Natural Medicines database:

Methotrexate + Activated Charcoal Apple Beer Grapefruit Siberian Cocklebur Sweet Orange Wine African Wild Potato + 74 more

major · moderate · minor — check everything you take with our drug–supplement interaction checker.

Check another combination

Our instant two-drug interaction checker is almost here.

Coming soon

The instant two-drug checker is on its way.

In the meantime, browse the directory below to look up any drug and see its documented interactions.

Still have questions about this combination?

Every question gets a real answer from a licensed pharmacist — free, and usually within a day.

Ask the pharmacist
This information is for education, not a substitute for professional medical advice. Do not start, stop, or change any medication without talking to your pharmacist or prescriber.