Elimination of indocyanine green by the liver of infants with hypertrophic pyloric stenosis and the icteropyloric syndrome

The role of UGT1A1*28 mutation in jaundiced infants with hypertrophic pyloric stenosis

Hypertrophic pyloric stenosis (HPS) may be accompanied by jaundice, a condition referred to as the icteropyloric syndrome (IPS). It has long been suspected that the etiology of IPS is an early manifestation of Gilbert's syndrome (GS). Clinical features common to both GS and IPS include jaundice precipitated by fasting and improved with feeding. Prevalence of jaundice in HPS is similar to that of clinically apparent GS in the general population. Discovery of a mutation in the promoter region of the bilirubin uridine diphosphate glucuronosyl transferase gene (UGT1A1*28) as the most common cause of GS has provided a tool to determine the role of GS in IPS. The aims of this study were to determine 1) the prevalence of IPS in a large group of infants with HPS, 2) whether disease severity contributed to the manifestation of IPS, and 3) whether GS played a role in IPS. Radioactive PCR and sequencing were used to determine the presence of UGT1A1*28 mutations. We determined a prevalence of IPS of 14.3% in HPS. Infants with IPS had significantly higher levels of alkalosis than infants with HPS alone. GS mutations were 4-fold higher in IPS (43.8%) than HPS (10.7%). In conclusion, the frequency of jaundice in HPS is similar to that of clinically apparent GS in the general population. Manifestation of IPS results from a more severe degree of metabolic disturbance and the presence of GS mutations.

Ontogeny of hepatic and renal systemic clearance pathways in infants: part I

Dramatic developmental changes in the physiological and biochemical processes that govern drug pharmacokinetics and pharmacodynamics occur during the first year of life. These changes may have significant consequences for the way infants respond to and deal with drugs. The ontogenesis of systemic clearance mechanisms is probably the most critical determinant of a pharmacological response in the developing infant. In recent years, advances in molecular techniques and an increased availability of fetal and infant tissues have afforded enhanced insight into the ontogeny of clearance mechanisms. Information from these studies is reviewed to highlight the dynamic and complex nature of developmental changes in clearance mechanisms in infants during the first year of life. Hepatic and renal elimination mechanisms constitute the two principal clearance pathways of the developing infant. Drug metabolising enzyme activity is primarily responsible for the hepatic clearance of many drugs. In general, when compared with adult activity levels normalised to amount of hepatic microsomal protein, hepatic cytochrome P450-mediated metabolism and the phase II reactions of glucuronidation, glutathione conjugation and acetylation are deficient in the neonate, but sulfate conjugation is an efficient pathway at birth. Parturition triggers the dramatic development of drug metabolising enzymes, and each enzyme demonstrates an independent rate and pattern of maturation. Marked interindividual variability is associated with their developmental expression, making the ontogenesis of hepatic metabolism a highly variable process. By the first year of life, most enzymes have matured to adult activity levels. When compared with adult values, renal clearance mechanisms are compromised at birth. Dramatic increases in renal function occur in the ensuing postpartum period, and by 6 months of age glomerular filtration rate normalised to bodyweight has approached adult values. Maturation of renal tubular functions exhibits a more protracted time course of development, resulting in a glomerulotubular imbalance. This imbalance exists until adult renal tubule function values are approached by 1 year of age. The ontogeny of hepatic biliary and renal tubular transport processes and their impact on the elimination of drugs remain largely unknown. The summary of the current understanding of the ontogeny of individual pathways of hepatic and renal elimination presented in this review should serve as a basis for the continued accruement of age-specific information concerning the ontogeny of clearance mechanisms in infants. Such information can only help to improve the pharmacotherapeutic management of paediatric patients.