Phenytoin therapy for epileptic children: evaluation of salivary and plasma concentrations and of methods of assessing compliance.

Monitoring phenytoin therapy in children is difficult because they fear blood sampling, yet frequent control of phenytoin levels may be necessary because of the age-dependence of phenytoin metabolism. In 22 patients aged between six and 15 years, phenytoin concentrations were studied in mixed saliva and parotid saliva and were compared with plasma levels from blood obtained at the same time. For mixed saliva, the saliva: plasma concentration ratio was 0.11 +/- SD 0.04 and in parotid saliva it was 0.10 +/- 0.06. In addition, compliance was studied in 13 children, each receiving between three and seven different quantities of phenytoin. Clinical judgement about compliance agreed well with the two laboratory measures. A graphic analysis of the relationship between plasma concentration and dosage is proposed as practical method of assessing compliance, because it appears to be both simple and reliable, and therefore suitable for routine use.