Drug interactions
Sulfamethoxazole + Valproic acid
Severity: Minor
Sulfamethoxazole and Valproic acid: minor 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
Valproate may weakly inhibit CYP2C9, which contributes to sulfamethoxazole metabolism, so levels could rise slightly. Clinical significance is likely small.
What this interaction means in plain words
Sulfamethoxazole and Valproic acid have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised.
Why it happens
Possible weak inhibition of CYP2C9 metabolism of sulfamethoxazole.
What to do
No routine action is needed; monitor for sulfonamide adverse effects such as rash or cytopenias during prolonged therapy.
What to ask your pharmacist
- Is there anything I should notice while taking both?
- Do I need to tell my doctor at the next visit?
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Other interactions of Valproic acid
- Ertapenem + Valproic acid Contraindicated
- Imipenem / cilastatin / relebactam + Valproic acid Contraindicated
- Imipenem / cilastatin + Valproic acid Contraindicated
- Meropenem / vaborbactam + Valproic acid Contraindicated
- Meropenem + Valproic acid Contraindicated
- Calcium / magnesium / potassium / sodium oxybates + Valproic acid Major
Frequently asked questions
Can I take Sulfamethoxazole with Valproic acid?
MediHelp rates the interaction as minor. Sulfamethoxazole and Valproic acid have a small, usually unimportant interaction. Most people can take both; the pharmacist may still mention it so that any unexpected effect is recognised. Valproate may weakly inhibit CYP2C9, which contributes to sulfamethoxazole metabolism, so levels could rise slightly. Clinical significance is likely small.
How serious is the interaction between Sulfamethoxazole and Valproic acid?
MediHelp rates it minor, on a four-level scale (minor, moderate, major, contraindicated) based on published labels and references. What to do, in brief: No routine action is needed; monitor for sulfonamide adverse effects such as rash or cytopenias during prolonged therapy.
What other medicines interact with Valproic acid?
MediHelp also lists interactions of Valproic acid with, for example, Ertapenem, Imipenem / cilastatin / relebactam, Imipenem / cilastatin. The full list is on the Valproic acid page.
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