Drug interactions
Fosinopril-hydrochlorothiazide + Trimethoprim
Severity: Major
Fosinopril-hydrochlorothiazide and Trimethoprim: major interaction.
Last updated Sources: US FDA label
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 with an ACE inhibitor this can cause clinically significant hyperkalemia. Risk is highest in older patients, those with renal impairment or diabetes, and with high trimethoprim doses.
What this interaction means in plain words
Fosinopril-hydrochlorothiazide 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.
Fosinopril-hydrochlorothiazide belongs to Cardiovascular; Trimethoprim belongs to Anti Bacterial.
Why it happens
Trimethoprim amiloride-like ENaC blockade combined with ACE inhibitor-induced aldosterone suppression reduces renal potassium excretion.
What to do
Avoid the combination in high-risk patients where alternatives exist. Otherwise check serum potassium and creatinine within a few days of starting and again during treatment.
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 Fosinopril-hydrochlorothiazide
- Aliskiren + Fosinopril-hydrochlorothiazide Contraindicated
- Dofetilide + Fosinopril-hydrochlorothiazide Contraindicated
- Fosinopril-hydrochlorothiazide + Protein a column Contraindicated
- Fosinopril-hydrochlorothiazide + Sacubitril / valsartan Contraindicated
- Aldesleukin + Fosinopril-hydrochlorothiazide Major
- Amifostine + Fosinopril-hydrochlorothiazide Major
Other interactions of Trimethoprim
Frequently asked questions
Can I take Fosinopril-hydrochlorothiazide with Trimethoprim?
MediHelp rates the interaction as major. Fosinopril-hydrochlorothiazide 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 with an ACE inhibitor this can cause clinically significant hyperkalemia. Risk is highest in older patients, those with renal impairment or diabetes, and with high trimethoprim doses.
How serious is the interaction between Fosinopril-hydrochlorothiazide 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: Avoid the combination in high-risk patients where alternatives exist. Otherwise check serum potassium and creatinine within a few days of starting and again during treatment.
What other medicines interact with Fosinopril-hydrochlorothiazide?
MediHelp also lists interactions of Fosinopril-hydrochlorothiazide with, for example, Aliskiren, Dofetilide, Protein a column. The full list is on the Fosinopril-hydrochlorothiazide page.
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