Phenobarbital in newborns with neonatal seizures. A study of plasma levels after intravenous administration.

Phenobarbital plasma levels were studied in a group of 25 newborn infants. Phenobarbital was administered i.v. in all cases throughout the study period. The mean loading dose was 19.4 mg/kg, ranging from 16.4 to 20.5, and the mean maintenance dose was 4.0 mg/kg/day, varying from 2.6 to 5.0. We obtained mean plasma levels of 22.9 micrograms/ml, 24 h after administering the loading dose. Mean plasma levels at 4, 7, 14 and 21 days were in the therapeutic range (15-40 micrograms/ml), with only a few cases falling outside of it. There was no difference in plasma phenobarbital levels between term and pre-term infants. Side effects were not seen in infants without a severe neurological impairment prior to drug administration.