PHOTOTHERAPY OF SEVERE UNCONJUGATED HYPERBILIRUBINEMIA: FORMATION AND REMOVAL OF LABELED BILIRUBIN DERIVATIVES

Abstract

Formation and disposition of the photodegradation products of bilirubin was studied in two infants with severe unconjugated hyperbilirubinemia (Crigler-Najjar syndrome) who responded to phototherapy with a marked and sustained fall of serum bilirubin. During exposure to light, tracer amounts of ¹⁴C-bilirubin were infused at constant rates for periods of 10 and 24 hours. Radioactivity in bilirubin and in its photoderivatives was determined in serially collected samples of plasma, urine, and bile. Direct evidence was obtained that light converts bilirubin in vivo to more polar, predominantly diazonegative, and presumably less toxic derivatives which are rapidly excreted in bile and urine without detectable retention in the plasma. These findings provide experimental support for the use of phototherapy in the management of hyperbilirubinemia in infants.