Drug interactions
Losartan + Sulfamethoxazole
Severity: Moderate
Losartan and Sulfamethoxazole: 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
Sulfamethoxazole inhibits CYP2C9, which helps convert losartan to its active metabolite E-3174, so antihypertensive effect could be modestly reduced. The clinical significance is not well established. Trimethoprim in co-trimoxazole also adds a hyperkalemia risk with losartan.
What this interaction means in plain words
Losartan and Sulfamethoxazole 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.
Why it happens
Sulfamethoxazole inhibits CYP2C9-mediated conversion of losartan to E-3174.
What to do
Monitor blood pressure response. If co-trimoxazole is used, also check serum potassium and creatinine.
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 Losartan
- Aliskiren + Losartan Contraindicated
- Losartan + Sparsentan Contraindicated
- Amifostine + Losartan Major
- Amiloride + Losartan Major
- Amlodipine-benazepril + Losartan Major
- Amlodipine-hydrochlorothiazide-valsartan + Losartan Major
Frequently asked questions
Can I take Losartan with Sulfamethoxazole?
MediHelp rates the interaction as moderate. Losartan and Sulfamethoxazole 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. Sulfamethoxazole inhibits CYP2C9, which helps convert losartan to its active metabolite E-3174, so antihypertensive effect could be modestly reduced. The clinical significance is not well established. Trimethoprim in co-trimoxazole also adds a hyperkalemia risk with losartan.
How serious is the interaction between Losartan and Sulfamethoxazole?
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 blood pressure response. If co-trimoxazole is used, also check serum potassium and creatinine.
What other medicines interact with Losartan?
MediHelp also lists interactions of Losartan with, for example, Aliskiren, Sparsentan, Amifostine. The full list is on the Losartan page.
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