Drug interactions
Captopril + Trimethoprim
Severity: Major
Captopril and Trimethoprim: major interaction.
Last updated Sources: UK SmPC
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 blocks epithelial sodium channels in the distal nephron and reduces potassium excretion, and captopril lowers aldosterone. Together they can cause clinically significant hyperkalemia, particularly in older adults or those with renal impairment.
What this interaction means in plain words
Captopril and Trimethoprim can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for.
Captopril belongs to Cardiovascular; Trimethoprim belongs to Anti Bacterial.
Why it happens
Additive reduction in renal potassium excretion via ENaC blockade and reduced aldosterone.
What to do
Check serum potassium and creatinine within a few days of starting trimethoprim and repeat as needed. Prefer an alternative antibiotic in high-risk patients.
What to ask your pharmacist
- Does the benefit of taking both outweigh the risk in my case?
- Do I need any blood test, ECG or other check while on both?
- What early warning signs should I watch for, and what should I do if they appear?
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References
Other interactions of Captopril
- Aliskiren + Captopril Contraindicated
- Captopril + Sacubitril / valsartan Contraindicated
- Captopril + Sacubitril-valsartan Contraindicated
- Amifostine + Captopril Major
- Amiloride + Captopril Major
- Amlodipine-hydrochlorothiazide-valsartan + Captopril Major
Other interactions of Trimethoprim
Frequently asked questions
Can I take Captopril with Trimethoprim?
MediHelp rates the interaction as major. Captopril and Trimethoprim can interact in a way that may be serious. Using them together is sometimes necessary, but it needs a deliberate decision by the prescriber, a plan for monitoring, and clear advice on the warning signs to watch for. Trimethoprim blocks epithelial sodium channels in the distal nephron and reduces potassium excretion, and captopril lowers aldosterone. Together they can cause clinically significant hyperkalemia, particularly in older adults or those with renal impairment.
How serious is the interaction between Captopril and Trimethoprim?
MediHelp rates it major, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: Check serum potassium and creatinine within a few days of starting trimethoprim and repeat as needed. Prefer an alternative antibiotic in high-risk patients.
What other medicines interact with Captopril?
MediHelp also lists interactions of Captopril with, for example, Aliskiren, Sacubitril / valsartan, Sacubitril-valsartan. The full list is on the Captopril page.
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