Elimination of phenytoin in toxic overdose

Phenytoin is widely used for the management of seizures. Fortunately overdo sage with this drug is rare. We performed a prospective study to investigat e the elimination kinetics of phenytoin in toxic overdose. All patients wer e only on phenytoin and not on other anticonvulsants. Phenytoin toxicity wa s defined by clinical features and correlated with drug levels. Daily pheny toin levels were obtained until they were less than or equal to 15 mcg/ml. Nine patients with age ranging from 20 to 66-years-old were recruited. Sex ratio was male:female, 5:4. Initial phenytoin levels ranged from 34 to 57.5 mcg/ml. Serum phenytoin levels of three patients remained relatively const ant for 2-5 days before declining in a steady fashion. Phenytoin levels of the remaining patients declined in an almost linear manner. Regression anal ysis of all patients showed that the slope terms were highly significant (w ith low P-values) and corresponding R-2 values were close to 1. Different p atients have different rates of metabolism; in seven of nine patients, leve ls declined between 4.6 and 5.9 mcg/ml per day. Knowledge of the rate of el imination assists the clinician in deciding on the best time to reinstitute phenytoin therapy. (C) 2000 Elsevier Science B.V. All rights reserved.