Comparison of phenytoin determinations in plasma, plasma dialysate and saliva for control of antiepileptic therapy in children.

Phenytoin was determined in plasma or serum, dialysate from plasma or serum and saliva in 45 children and 7 adults by gas chromatography. 200 microliter of plasma were necessary for dialysis. Close correlations were found between phenytoin concentrations in the different media (r greater than or equal to 0.95). Since in some cases the levels in saliva were extremely high in comparison to plasma and dialysate, precautions are advisable when using phenytoin determinations in saliva for therapeutic decisions. Clinical data from 15 children with high phenytoin levels suggest that there is no advantage in determining the unbound fraction of the drug in plasma for the control of antiepileptic therapy.