Drug interactions
Metformin + Trimethoprim
Severity: Moderate
Metformin and Trimethoprim: moderate interaction.
Last updated
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
Trimethoprim can raise metformin plasma concentrations by reducing its renal elimination. Higher metformin exposure may increase the risk of gastrointestinal effects and, particularly in patients with renal impairment, lactic acidosis.
What this interaction means in plain words
Metformin and Trimethoprim can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken.
Metformin belongs to Endocrine; Trimethoprim belongs to Anti Bacterial.
Why it happens
Trimethoprim inhibits renal tubular transporters OCT2 and MATE1/MATE2-K, reducing tubular secretion of metformin.
What to do
Monitor renal function and glycemic control, and watch for signs of metformin excess such as nausea or malaise. Consider reducing the metformin dose in patients with reduced eGFR or when trimethoprim is given long term.
What to ask your pharmacist
- Should I take them at different times of day?
- Does the dose of either medicine need to change?
- Is there anything I should avoid, such as alcohol or certain foods, while on both?
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Other interactions of Metformin
Other interactions of Trimethoprim
Frequently asked questions
Can I take Metformin with Trimethoprim?
MediHelp rates the interaction as moderate. Metformin and Trimethoprim can affect each other. The combination is often manageable, but it may need a change of dose, a change of timing, or extra checks while both are taken. Trimethoprim can raise metformin plasma concentrations by reducing its renal elimination. Higher metformin exposure may increase the risk of gastrointestinal effects and, particularly in patients with renal impairment, lactic acidosis.
How serious is the interaction between Metformin and Trimethoprim?
MediHelp rates it moderate, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Monitor renal function and glycemic control, and watch for signs of metformin excess such as nausea or malaise. Consider reducing the metformin dose in patients with reduced eGFR or when trimethoprim is given long term.
What other medicines interact with Metformin?
MediHelp also lists interactions of Metformin with, for example, Contrast media, Diatrizoate meglumine / diatrizoate, Diatrizoate. The full list is on the Metformin page.
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