Subtherapeutic dicloxacillin levels in a neonate: Possible mechanisms

A neonate treated initially with oxacillin intravenously for two weeks and who was receiving phenobarbital for a seizure disorder subsequently failed to achieve therapeutic levels of orally administered dicloxacillin, even when the dosage was as high as 175 mg/kg/day. Intestinal absorption was documented by high serum peak levels. The low trough levels correlated with a high urinary excretion rate. The possibility that renal tubular transport of dicloxacillin was stimulated by administration of penicillin derivatives (and/or phenobarbital) is suggested, and the need for careful monitoring of serum levels of antibiotics in neonates is emphasized.