Acute onset of a tonic seizure in a phenytoin-overdosed patient who had taken phenytoin and levetiracetam daily.

The 42-year-old woman who had been taking 300 mg phenytoin and 2,000 mg levetiracetam daily took 28.6 g of phenytoin and was transferred to our critical care center. The blood phenytoin concentration was 67.9 μg/mL on admission and decreased to 53.4 μg/mL on hospital day 2. Tonic seizures occurred several times on hospital day 2; thus, we resumed levetiracetam via a nasogastric tube. Thereafter, no further seizures were observed. We thought the seizure to have been caused by temporary withdrawal of levetiracetam because it did not occur on the day when the blood phenytoin concentration peaked and stopped altogether after resumption of levetiracetam. We considered that to treat the convulsion attack resulting from an overdose of the other antiepileptic drug with a different action mechanism, it was necessary to promptly restart the administration of the antiepileptic drug, which the patient was usually administered.