INTRODUCTION: We report a possible case of gabapentin induced phenytoin toxicity. CASE REPORT: White man, 26 years old, chronically treated with phenytoin (for the past 4 years) and gabapentin (for the past 17 months). He was seen after complaining of dysarthria, ataxia and vertigo for the past 3 months, although having noted slight dizziness and a general, though undefined, indisposition from the start of taking gabapentin. The total and free serum levels of phenytoin found were clearly toxic. Gabapentin was discontinued definitively, and phenytoin for the next 7 days. The clinical symptoms had disappeared completely and phenytoin returned to within therapeutic levels. According to the criteria of causation it can be considered a possible adverse reaction caused by phenytoin related to incorporation of gabapentin. The mechanisms of this possible drug interaction are discussed, with emphasis on cytochrome P450 metabolism. CONCLUSION: The present case is a warning of the possible interaction of a drug (gabapentin) not contemplated when starting or when monitoring an antiepileptic treatment.
INTRODUCTION: We report a possible case of gabapentin induced phenytointoxicity. CASE REPORT: White man, 26 years old, chronically treated with phenytoin (for the past 4 years) and gabapentin (for the past 17 months). He was seen after complaining of dysarthria, ataxia and vertigo for the past 3 months, although having noted slight dizziness and a general, though undefined, indisposition from the start of taking gabapentin. The total and free serum levels of phenytoin found were clearly toxic. Gabapentin was discontinued definitively, and phenytoin for the next 7 days. The clinical symptoms had disappeared completely and phenytoin returned to within therapeutic levels. According to the criteria of causation it can be considered a possible adverse reaction caused by phenytoin related to incorporation of gabapentin. The mechanisms of this possible drug interaction are discussed, with emphasis on cytochrome P450 metabolism. CONCLUSION: The present case is a warning of the possible interaction of a drug (gabapentin) not contemplated when starting or when monitoring an antiepileptic treatment.