Methenamine and Furosemide Injection: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Furosemide Injection
Methenamine
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.
What happens
An increased risk of insoluble precipitate with formaldehyde in the urine
Interaction Deep Dive
Concurrent administration of methenamine and a sulfonamide is contraindicated. Concomitant use may form an insoluble precipitate with formaldehyde in the urine12.
Why it happens (mechanism)
Formation of an insoluble precipitate in urine
Common questions
Can I take Methenamine and Furosemide Injection together?
An increased risk of insoluble precipitate with formaldehyde in the urine Always confirm with your pharmacist or prescriber before making any change.
How serious is the Methenamine and Furosemide Injection interaction?
It is rated contraindicated. These should generally not be used together.
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.
Questions for your pharmacist
- Does my dose of Methenamine or Furosemide Injection 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)
- Product Information: METHENAMINE MANDELATE oral film coated tablets, methenamine mandelate oral film coated tablets. Chartwell RX LLC (per Dailymed), Congers, NY, 2023. DailyMed
- Product Information: HIPREX(R) oral tablets, methenamine hippurate oral tablets. Validus Pharmaceuticals LLC (per FDA), Parsippany, NJ, 2017. DailyMed
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