Drug interactions
phenytoin + trimethoprim-sulfamethoxazole
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.
Overview
↑ phenytoin levels → toxicity.
Mechanism of action
CYP2C9 inhibition/displacement.
Clinical management
Avoid or reduce phenytoin with level monitoring.
Drug reference
References
Frequently asked questions
Can I take phenytoin with trimethoprim-sulfamethoxazole?
The interaction is rated: Major. ↑ phenytoin levels → toxicity.
How serious is the interaction between phenytoin and trimethoprim-sulfamethoxazole?
The interaction is rated: Major. Evidence level: High.
How is the interaction between phenytoin and trimethoprim-sulfamethoxazole managed?
Avoid or reduce phenytoin with level monitoring.
Why do phenytoin and trimethoprim-sulfamethoxazole interact?
CYP2C9 inhibition/displacement.
Full monographs, dosing and an interaction checker in the MediHelp app
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