Paradoxical seizures in phenytoin toxicity.

Phenytoin toxicity is an uncommon problem seen in clinical practice. The predisposing factors for toxicity are hypoalbuminemia, chronic renal failure, hepatic dysfunction and drugs which interfere with phenytoin metabolism. Common manifestations of toxicity, like confusion and ataxia, are well known. A less well known phenomenon is paradoxical seizures. In this condition, seizures develop as the serum phenytoin level rises and decrease in frequency as levels drop. It may or may not be accompanied by other features of toxicity. We present three patients with paradoxical seizures; their serum phenytoin levels were 43.5 mcg/mL, 46.5 mcg/mL and 38.3 mcg/mL. In all cases, seizures were controlled by withdrawal of phenytoin and reduction of drug levels.