Metabolism of bilirubin and riboflavin in the course of phototherapy for hyperbilirubinaemia in the newborns.

The study of bilirubin photochemical degradation in the presence of riboflavin has shown that, in this case, the primary process is photooxidation during which riboflavin acts as a receptor and bilirubin as a donor of electrons. The reaction proceeds under anaerobic conditions in an equilibrated manner, under aerobic ones as a catalytic process during which the catalyst, i. e., riboflavin is regenerated. The primary intermediate product is biliverdin in vitro, later this is further broken down. For the purpose of studying the mechanism of this process liquid chromatography and computerized technique based on solving nonlinear differential equations have been used. It appears that during phototherapy in the newborn infant there develops a decrease of the blood level of riboflavin reaching up to hypovitaminotic values and a transient biliverdin level elevation. Oral riboflavin administration may maintain this level within physiological range and at the same time shorten the necessary duration of phototherapy. In severe cases of hyperbilirubinaemia a shift of the ratio between flavin-adenin-dinucleotide and free riboflavin, as compared to the physiological state, has been recorded. The results of this work are discussed in the light of our current knowledge concerning the mechanisms of bilirubin breakdown during prototherapy.