Correlation between the saliva and free serum concentration of phenobarbital in epileptic children.

Twenty epileptic children taking phenobarbital (PB) were evaluated for the concentration of PB in their saliva (Sa), total serum concentration (TS), free serum concentration (FS), and also the pH of the saliva samples. The Sa/TS ratio was 43.0 +/- 5.2% (mean +/- SD), and showed a close relationship between the two (r = 0.98). The free serum concentrations for PB were also observed to be closely correlated to the saliva concentration (r = 0.99), as well as to the total serum concentration, with the FS/TS ratio being 45.0 +/- 5.6%. However, no obvious relationship between the salivary pH and the Sa/TS ratio for PB was observed. This suggested the usefulness of monitoring the PB saliva concentrations in clinical management of epilepsy.