Drug interactions
Metformin + Sulfamethoxazole
Severity: Moderate
Metformin and Sulfamethoxazole: 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 in co-trimoxazole inhibits renal tubular cation transporters (MATE and OCT2) and can raise metformin levels, while sulfonamides can occasionally cause hypoglycemia. Higher metformin exposure may raise the risk of gastrointestinal effects and rarely lactic acidosis, especially with renal impairment.
What this interaction means in plain words
Metformin and Sulfamethoxazole 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.
Why it happens
Inhibition of renal tubular secretion of metformin (via the trimethoprim component) reduces its clearance.
What to do
Monitor renal function and blood glucose during co-trimoxazole therapy and consider reducing the metformin dose in patients with reduced eGFR.
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
Frequently asked questions
Can I take Metformin with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Metformin and Sulfamethoxazole 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 in co-trimoxazole inhibits renal tubular cation transporters (MATE and OCT2) and can raise metformin levels, while sulfonamides can occasionally cause hypoglycemia. Higher metformin exposure may raise the risk of gastrointestinal effects and rarely lactic acidosis, especially with renal impairment.
How serious is the interaction between Metformin and Sulfamethoxazole?
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 blood glucose during co-trimoxazole therapy and consider reducing the metformin dose in patients with reduced eGFR.
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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