[Effect of minimal doses of phenobarbital on bilirubinemia in the newborn infant].

To evaluate the effect of lower than usual doses of phenobarbital on prevention of hyperbilirubinemia in the neonate, a study was carried out in neonates with subnormal weight and of similar characteristics regarding gestational age, intrauterine growth, absence of pathology, type and amount of milk formula ingested and values for indirect serum bilirubin previous to the initiation of the administration of phenobarbital on their second day of life; they were separate at random into three groups according to the dose of phenobarbital given (1 mg, 3 mg and 5 mg per kilo and per day, respectively) and were numerically distributed in similar manner. In all groups, serum indirect bilirubin rate was confirmed to be practically the same; the differences did not show statistical significance from the 2nd to the 6th day of life, when the study was done. As preventive of neonatal hyperbilirubinemia, the drug is efficient at doses as low as 1 mg/kg/day. It is believed that similar responses with different low doses of phenobarbital is due to the fact that the drug enzymatic induction phenomenon is brought forward, even at minimal doses, such as has been demonstrated through experiences in animals where the effect is produced even with doses of micrograms per kilogram of weight.