Studies suggest that ciprofloxacin, clinafloxacin, and enoxacin do not usually have a clinically significant effect on
phenytoin levels. However, case reports describe both a rise and a fall in
phenytoin levels in patients given ciprofloxacin. Fosphenytoin, a prodrug of
phenytoin, may interact similarly.
The
clinical importance of these changes in levels is unknown, but bear them in mind in case of an unexpected response to treatment. It has been suggested that it may be prudent to monitor
phenytoin levels in those given ciprofloxacin.
Quinolones alone very occasionally cause convulsions, therefore they should be used with caution in patients with epilepsy.