Effects of phenobarbital on early intellectual and behavioral development: a concordant twin case study.

A Monozygotic twin pair had febrile seizures, only one was treated with phenobarbital from 17-30 months of age. Standard intellectual and behavioral assessments were conducted during Treatment (30 months of age), and Post-Treatment (32, 41, 48, 66 months of age). Both twins showed normal global intelligence at all assessments, however, the phenobarbital twin scored lower at all assessments. Differences in specific abilities were also seen during Post-Treatment. When phenobarbital was withdrawn, the treated twin's behavior showed immediate improvement. This experience suggests that early phenobarbital treatment may affect global intelligence through the preschool period, but that the effect is not severe. Phenobarbital also may adversely affect behavior, although the effect disappears with termination of the drug.