Drug interactions
Hydrochlorothiazide + Trimethoprim
Severity: Moderate
Hydrochlorothiazide 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
Both thiazides and trimethoprim can lower serum sodium, and the combination has been associated with clinically significant hyponatremia, particularly in older adults. Trimethoprim can also raise potassium through its amiloride-like effect, which may partly offset thiazide potassium loss.
What this interaction means in plain words
Hydrochlorothiazide 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.
Hydrochlorothiazide belongs to Cardiovascular; Trimethoprim belongs to Anti Bacterial.
Why it happens
Additive effects on sodium handling: thiazide inhibition of the distal NaCl cotransporter and trimethoprim blockade of epithelial sodium channels.
What to do
Check serum sodium and potassium within the first week or so of combined therapy, especially in elderly patients. Stop or change the antibiotic or diuretic if hyponatremia or hyperkalemia develops.
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 Hydrochlorothiazide
Other interactions of Trimethoprim
Frequently asked questions
Can I take Hydrochlorothiazide with Trimethoprim?
MediHelp rates the interaction as moderate. Hydrochlorothiazide 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. Both thiazides and trimethoprim can lower serum sodium, and the combination has been associated with clinically significant hyponatremia, particularly in older adults. Trimethoprim can also raise potassium through its amiloride-like effect, which may partly offset thiazide potassium loss.
How serious is the interaction between Hydrochlorothiazide 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: Check serum sodium and potassium within the first week or so of combined therapy, especially in elderly patients. Stop or change the antibiotic or diuretic if hyponatremia or hyperkalemia develops.
What other medicines interact with Hydrochlorothiazide?
MediHelp also lists interactions of Hydrochlorothiazide with, for example, Dofetilide, Amifostine, Amiodarone. The full list is on the Hydrochlorothiazide page.
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