Drug interactions
ciprofloxacin + phenytoin
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
Ciprofloxacin has been reported to alter phenytoin concentrations (increase or decrease), risking toxicity or breakthrough seizures; fluoroquinolones may also lower seizure threshold.
Mechanism of action
Unknown; variable effect on phenytoin exposure (possible altered metabolism/absorption). Fluoroquinolones can lower seizure threshold independent of phenytoin levels.
Clinical management
Monitor total and/or free phenytoin concentrations and clinical response when starting or stopping ciprofloxacin; adjust phenytoin dose as needed. Consider alternative antibiotic if seizure control is unstable.
Drug reference
References
- Ciprofloxacin: Drug Interactions — Lexicomp
- Phenytoin: Drug Interactions — Lexicomp
- Ciprofloxacin US Prescribing Information — FDA Label
Frequently asked questions
Can I take ciprofloxacin with phenytoin?
The interaction is rated: Moderate. Ciprofloxacin has been reported to alter phenytoin concentrations (increase or decrease), risking toxicity or breakthrough seizures; fluoroquinolones may also lower seizure threshold.
How serious is the interaction between ciprofloxacin and phenytoin?
The interaction is rated: Moderate. Evidence level: Moderate.
How is the interaction between ciprofloxacin and phenytoin managed?
Monitor total and/or free phenytoin concentrations and clinical response when starting or stopping ciprofloxacin; adjust phenytoin dose as needed. Consider alternative antibiotic if seizure control is unstable.
Why do ciprofloxacin and phenytoin interact?
Unknown; variable effect on phenytoin exposure (possible altered metabolism/absorption). Fluoroquinolones can lower seizure threshold independent of phenytoin levels.
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