Drug interactions
Cimetidine + Trimethoprim
Severity: Moderate
Cimetidine 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
Cimetidine can reduce renal secretion of trimethoprim and raise its concentrations. Higher levels may increase the risk of hyperkalemia and bone marrow suppression, particularly in renal impairment or at high doses.
What this interaction means in plain words
Cimetidine 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.
Cimetidine belongs to Gastrointestinal Tract; Trimethoprim belongs to Anti Bacterial.
Why it happens
Competition for renal tubular cationic secretion lowers trimethoprim clearance.
What to do
Monitor serum potassium, creatinine and blood counts in at-risk patients receiving prolonged or high-dose trimethoprim.
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 Cimetidine
- Cimetidine + Dofetilide Contraindicated
- Cimetidine + Fezolinetant Contraindicated
- Alfentanil + Cimetidine Major
- Atazanavir + Cimetidine Major
- Carmustine + Cimetidine Major
- Cimetidine + Citalopram Major
Other interactions of Trimethoprim
Frequently asked questions
Can I take Cimetidine with Trimethoprim?
MediHelp rates the interaction as moderate. Cimetidine 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. Cimetidine can reduce renal secretion of trimethoprim and raise its concentrations. Higher levels may increase the risk of hyperkalemia and bone marrow suppression, particularly in renal impairment or at high doses.
How serious is the interaction between Cimetidine 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 serum potassium, creatinine and blood counts in at-risk patients receiving prolonged or high-dose trimethoprim.
What other medicines interact with Cimetidine?
MediHelp also lists interactions of Cimetidine with, for example, Dofetilide, Fezolinetant, Alfentanil. The full list is on the Cimetidine page.
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