Use of activated charcoal to reduce elevated serum phenobarbital concentration in a neonate. The course of a neonate administered activated charcoal orally for elevated phenobarbital concentration is described. The neonate required a serum concentration of phenobarbital eventually exceeding 80 micrograms/mL for seizure control. However, due to the severe CNS injury as a result of the asphyxia at birth, a diagnosis of cerebral death by electroencephalogram and apnea test was pursued. This required the phenobarbital concentration to be less than 30 micrograms/mL. Serial phenobarbital concentrations during this time indicated a 250 hour half-life, which would require two weeks for the phenobarbital to drop below 30 micrograms/mL. With the administration of six doses of activated charcoal at 0.7 g/kg/dose, the phenobarbital serum concentration decreased to 22 micrograms/mL, giving an estimated phenobarbital half-life of 22 hours. This, and two other subsequent cases, indicates repeated doses of activated charcoal are effective in augmenting the clearance of certain drugs in the neonatal age group. 