Ticlopidine-induced phenytoin toxicity.

OBJECTIVE

To report a probable case of ticlopidine-induced phenytoin toxicity.

CASE SUMMARY

A 72-year-old white man suddenly developed combative behavior, refused to leave his room, stopped eating, and began falling to the floor 6 weeks after being given ticlopidine. The total phenytoin concentration was measured at 43.6 micrograms/mL; the dosage of phenytoin was decreased and the symptoms later resolved. After ticlopidine was discontinued, the patient was rechallenged with the same dose of phenytoin without symptoms of toxicity.

DISCUSSION

Possible mechanisms of the drug interaction are discussed with emphasis on cytochrome P450 metabolism.

CONCLUSIONS

Clinicians should be aware of this potentially serious drug interaction and either avoid the phenytoin-ticlopidine combination, or monitor closely for phenytoin toxicity.