Developmental changes in serum half-life of (EZ)-cyclobilirubin

Background Phototherapy has been a standard treatment for neonatal hyperbilirubinemia for more than 40 years, but it has remained sub-optimal. Aims To clarify the developmental changes in parameters of (4 E , 15 Z )-cyclobilirubin (( EZ )-C) elimination in order to obtain basic data for establishing optimal phototherapy. Study design Blood samples were taken at regular intervals after stopping phototherapy, and bilirubin fractions were analyzed by high-performance liquid chromatography. Subjects and methods The subjects were 46 infants with hyperbilirubinemia who underwent phototherapy. The gestational age and birth weight of the subjects ranged from 25.0 to 41.0 weeks and from 656 to 3810 g, respectively, and the age at cessation of phototherapy was a median of 5 days. A kinetic model of ( EZ )-C elimination was established, and the serum half-life of ( EZ )-C was calculated on the basis of the determined model. Relationships of the half-life of ( EZ )-C with birth weight and gestational age were investigated. Results Serum ( EZ )-C elimination followed a first-order kinetic model in 43 infants and a zero-order kinetic model in three extremely low birth weight infants. The half-life of ( EZ )-C calculated on the basis of a first-order elimination model in serum ranged from 68 to 274 min and showed weak negative correlations with birth weight and gestational age. Conclusions Serum ( EZ )-C excretion followed a first-order kinetic model in most of the neonates. The half-life of ( EZ )-C becomes more prolonged in the very low birth weight infant and early gestational age.