[Blood levels of phenytoin. Pharmacokinetics and individualization of dosages in controlled children with crises and with persistence of crises]. / Niveles séricos de fenitoína. Farmacocinética e individualización de dosis en niños con crisis controlados y con persistencia de las crisis.

The pharmacokinetics of phenytoin was evaluated using the Michaelis-Menten technique in children with seizures seen at the Outpatient Ward, in order to adjust their medication dosages based on a clinical-pharmacological relation. The children were divided into two groups: Group A (controlled seizures) and group B (persistent seizures). Each group of children were orally given 7 mg/kg of phenytoin. Their serum levels were measured using enzymatic immunoassay at one, two, four, eight and 12 hours after taking the medication. There was a significant correlation (P less than 0.05) between the average saturation constant (Km) and the maximum speed (Vmax) with age and the doses administered in group A, which showed a lesser metabolic capacity than group B. There was also a significant correlation (P less than 0.05) when predicting the levels in each group. Clinically, the patients group A were controlled while those in group B witnessed a lesser frequency and intensity of the seizures in six patients, two were controlled and two others remained the same. The data shows a clinical-pharmacological correlation in children difficult to control, and improves the dosaging criteria used each individuals needs.