Pharmacokinetics of phenytoin in acute adult and child intoxication

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Abstract
The pharmacokinetics of phenytoin was studied in 4 acute intoxications. Two patients were identical twins aged 2 years 5 months being concomitantly poisoned, whereas one adult male was admitted twice. Their maximal phenytoin plasma concentrations were 246, 200, 168 and 164 umol/1; the lowest values were in the twins. Despite this, consciousness in the children was more depressed whereas severe ataxia and involuntary movements dominated the course in the adult. All patients survived without any sequelae upon symptomatic treatment. Saturation kinetics of phenytoin could be demonstrated in all cases. For the twins, a Km in the range of 10.3 - 48.6 umol/1 was calculated, indicating saturation kinetics even within the therapeutic range of 40 - 80 umol/1. In the twins, the Vmax was in the range of 47.3 - 79.4 umol/1/day with a maximal elimination rate of 37.7 - 63.6 umol/kg/day. We suggest that these kinetic parameters for phenytoin probably are independent of age.