Phenobarbital therapy in neonatal seizures and the prognostic value of the EEG

High plasma levels of phenobarbital are known to produce profound effects on the EEG background activity. Phenobarbital therapy frequently is administered to the neonate with seizures prior to the first EEG recording. Therefore, it is questionable whether in these neonates alterations of the EEG background activity are related to anticonvulsive therapy. A total of 26 neonates with seizures had an EEG while on phenobarbital therapy. In five cases an EEG was available prior to this treatment. Suppression of the background activity in the EEG was seen in 17 neonates of whom two had an inactive tracing and three a burst-suppression pattern. Moderate suppression occurred in five infants, mild suppression is seven infants. The suppression of the background activity correlated with the clinical outcome. The phenobarbital plasma levels in the group with severe or moderate suppression, mild suppression and normal background activity did not show statistically significant differences. Thus, the suppression of the EEG background activity in neonates with phenobarbital plasma levels of 1.3 to 5.9 mg/dl are secondary to brain pathology rather than medication.