Drug interactions
Hydrochlorothiazide-losartan + Trimethoprim
Severity: Major
Hydrochlorothiazide-losartan and Trimethoprim: major 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 reduces potassium excretion and, with an ARB, can cause clinically significant hyperkalemia, particularly with renal impairment, diabetes, older age or high doses. Hydrochlorothiazide partly offsets this, but not reliably.
What this interaction means in plain words
Hydrochlorothiazide-losartan 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.
Hydrochlorothiazide-losartan belongs to Cardiovascular; Trimethoprim belongs to Anti Bacterial.
Why it happens
Trimethoprim blocks epithelial sodium channels in the distal nephron, impairing potassium secretion, additive to ARB-mediated reduction of aldosterone.
What to do
Check serum potassium and creatinine within several days of starting trimethoprim and avoid in high-risk patients where alternatives exist. Use the shortest course and lowest dose possible.
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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Other interactions of Hydrochlorothiazide-losartan
- Aliskiren + Hydrochlorothiazide-losartan Contraindicated
- Dofetilide + Hydrochlorothiazide-losartan Contraindicated
- Hydrochlorothiazide-losartan + Sparsentan Contraindicated
- Aceclofenac + Hydrochlorothiazide-losartan Major
- Aldesleukin + Hydrochlorothiazide-losartan Major
- Amifostine + Hydrochlorothiazide-losartan Major
Other interactions of Trimethoprim
Frequently asked questions
Can I take Hydrochlorothiazide-losartan with Trimethoprim?
MediHelp rates the interaction as major. Hydrochlorothiazide-losartan 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 reduces potassium excretion and, with an ARB, can cause clinically significant hyperkalemia, particularly with renal impairment, diabetes, older age or high doses. Hydrochlorothiazide partly offsets this, but not reliably.
How serious is the interaction between Hydrochlorothiazide-losartan 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 several days of starting trimethoprim and avoid in high-risk patients where alternatives exist. Use the shortest course and lowest dose possible.
What other medicines interact with Hydrochlorothiazide-losartan?
MediHelp also lists interactions of Hydrochlorothiazide-losartan with, for example, Aliskiren, Dofetilide, Sparsentan. The full list is on the Hydrochlorothiazide-losartan page.
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