Neonatal hyperbilirubinemia

Effects of obstructive jaundice on the peripheral nerve: an ultrastructural study in rats

Obstructive jaundice (OJ) and hepatic disorders have been shown to be associated with peripheral neuropathy in several clinical studies. The study evaluated the effect of OJ on the ultrastructure of the rat sciatic nerve. In the OJ group, jaundice was created by ligation of common bile duct in Wistar-Albino rats. In the sham-operated control group the same procedure was performed without ligation of the bile duct. On day 7, all rats were re-operated and sciatic nerves were explored to harvest 2-cm-long nerve segments for quantitative and qualitative histopathological analysis by light and electron microscopy. Bilirubin was measured on serum samples. Bilirubin levels were significantly higher in jaundiced rats compared with that of controls (8.46 +/- 0.45 vs. 0.80 +/- 0.14 mmol/l, means +/- SD, p < 0.01). Control nerves did not show anything other than the normal histology. In the OJ group, degenerative changes such as irregularities, thinning, ruffling and invaginations, irregularshaped bodies, vacuolizations and focal segmental demyelination were observed in the myelin sheath. Myelin clusters were noted in the axoplasm. A varying degree of swelling was noted in the nucleus and cytoplasm of the Schwann cells. Morphometric analysis of specimens obtained from sciatic nerves showed that myelin injury (370.9 +/- 51.3 vs. 11.6 +/- 0.5 axons), axonal edema (142.1 +/- 24.2 vs. 10.6 +/- 0.5 edematous axons) and Schwann cell degeneration (50.3 +/- 11.6 vs. 3.2 +/- 0.2 Schwann cells) was significantly higher in the jaundiced rats than in the control group (p < 0.01). The ultrastructural alterations spotted in the rat peripheral nerve were attributed to hyperbilirubinemia and increased concentrations of several neurotoxic substances released from the Kupffer cells in OJ. Neuropathy in jaundiced patients seems to result from accompanying degenerative changes in the peripheral nervous system. However, the exact nature and initiating factors of this nerve injury remains to be unveiled.

Relation of peak total serum bilirubin concentrations to neurodevelopmental outcome at 2 years of age in premature African neonates

As part of a wider survey of the neurodevelopmental outcome of neonates who received intensive care for various morbidities in the Middle-Belt region of Nigeria, the relationship between peak total serum bilirubin (PTSB) concentrations in the neonatal period and neurodevelopmental status at 2 years of age was evaluated in 159 children available for follow-up and assessment. The prevalence of handicaps (minor and major) increased consistently with increase in the PTSB concentration, commencing in the range of 151-200 mumol/l. Major handicaps evolved in association with PTSB concentrations above 201 mumol/l. The handicaps consisted mainly of cerebral palsy and mental retardation. Children with handicaps (minor and major) experienced greater PTSB concentrations than those with a normal neurodevelopmental outcome. The emergence of major handicaps from a mean (SD) moderate peak hyperbilirubinaemia of 241.1 (35.9) mumol/l in the African neonate is worthy of note and cause for concern.

Auditory nerve of the normal and jaundiced rat. I. Spontaneous discharge rate and cochlear nerve histology

Hyperbilirubinemia is a major problem in neonatal intensive care. Hearing impairment is one of its sequelae. Although lesions of the central auditory pathways are known to be associated with this disorder in both humans and homozygous Gunn rats, the presence of cochler pathology is still controversial. The purpose of this study was to examine the functional integrity of the peripheral auditory system in the Gunn rat. The Gunn rat is a mutant of the Wistar strain with congenital deficiency of the liver enzyme uridine diphosphoglucuronyl transferase which is essential for bilirubin conjugation. This deficiency is inherited as an autosomal recessive trait, with the homozygous animals (jj) showing evidence of bilirubin encephalopathy. The heterozygotes (Jj) have 50% enzyme deficiency and are not jaundiced. The Long-Evans rat served as a control. The approach was to study the discharge characteristics fo single auditory nerve fibers using standard procedures in a closed and calibrated sound system. Various response measurements which would reveal pathological processes in the cochlea were analyzed. In this study, spontaneous discharge rate distribution and interspike interval statistics derived from Gunn rat auditory nerve recordings were found to be within the normal range, and cochlear nerve histology showed no evidence of neuropathy.

Breast mild jaundice: natural history, familial incidence and late neurodevelopmental outcome of the infant

Jaundice associated with breast feeding is a frequent problem facing the paediatrician. Despite numerous reports on this subject, the natural history, familial occurrence and late neurodevelopment of children with breast milk jaundice remain unclear. The follow up of 60 infants with breast milk jaundice showed that there are two bilirubin peaks, on the 4th and 5th day and on the 14th-15th day of life. In the infants with uninterrupted breast feeding, the hyperbilirubinaemia disappeared slowly and could still be detected 12 weeks after birth. The familial incidence of 13.9%, indicating that in some cases a unique genetic factor is expressed. Late neurodevelopment or hearing defects were not observed, thus enabling the paediatrician to encourage continuation of breast feeding in most cases of healthy infants with breast milk jaundice.

Drugs in human milk. Clinical pharmacokinetic considerations

Drugs ingested by a lactating mother would be expected to appear in human milk to some extent and be ingested by a breast-feeding infant. Drugs pass from maternal plasma into milk by passive diffusion and are distributed within the aqueous, protein and lipid phases of milk. Distribution into milk will be affected by physiochemical characteristics of the drug: acid-base characteristics, relative protein binding in plasma and milk, and lipid solubility, as well as milk composition. The milk-to-plasma concentration ratio is the most commonly quoted index of drug distribution into human milk. However, calculation of the daily infant dose of drug ingested in milk, and from this the dose in milk relative to the maternal dose on a weight-adjusted basis, is a more relevant indicator of infant exposure to a drug. This is particularly true for drugs with a high volume of distribution, for which only a small proportion of the mother's dose is contained within the plasma and available for distribution into milk. A better indication of infant exposure to a drug is the steady-state plasma drug concentration in a breast-feeding infant, the major determinants of which are the dose rate (via milk) and the oral availability and clearance in the infant. Although in neonates the rate of absorption may be different from adults, there is little evidence that its extent is significantly different. Clearance, however, is impaired in very young infants, particularly if premature. The decreased clearance would result in a proportional increase in steady-state plasma concentrations in the breast-feeding infant. Consideration of the dose ingested in milk and the approximate clearance in infants of different ages allows estimation of likely steady-state plasma concentrations in breast-feeding infants. From these considerations, recommendations regarding the safety of drugs during breast-feeding can be made. Drugs which are very toxic or have dose-independent toxicity should be considered separately. Recommendations regarding 'social' drugs such as nicotine, alcohol, caffeine and theobromine are particularly difficult, as doses are uncontrolled and vary variable.

Principles of drug biodisposition in the neonate. A critical evaluation of the pharmacokinetic-pharmacodynamic interface (Part I)

Rational pharmacotherapy is dependent upon an understanding of the clinical pharmacokinetic and pharmacodynamic properties of the drugs employed. Although the available data on drug biodisposition and action in the neonate have increased considerably in the last few years, pharmacokinetic-pharmacodynamic interactions for many drugs remain poorly understood. The ontogeny of drug absorption, distribution, metabolism, and elimination are addressed in this review. Drug absorption from any site depends upon both the physicochemical properties of the drug and a variety of patient factors. Absorption of orally administered drugs may be affected by changes in gastric acidity and emptying time as well as by bile salt pool size, bacterial colonisation, and extraintestinal disease states such as congestive heart failure. Factors affecting drug absorption following intramuscular, percutaneous, and rectal administration are also discussed. Drug distribution in the neonate is influenced by a variety of important and predictable age-dependent factors. The developmental aspects of protein binding and body water compartments are described. Additionally, hepatic drug metabolism assumes an important role in understanding the pharmacokinetic and pharmacodynamic properties of many compounds. Certain biotransformation pathways, including hydroxylation by the P450 mono-oxygenase system and glucuronidation, demonstrate only limited activity at birth, while other pathways, such as sulphate or glycine conjugation, appear very efficient at birth. Elimination of drugs excreted unchanged in the urine is dramatically reduced in the newborn, compared with older infants and children, due to immaturity of both glomerular filtration and tubular secretory processes. The glomerular filtration rate remains markedly reduced prior to 34 weeks gestational age, increasing as a function of post-conceptual age until adult values are achieved by approximately 2.5 to 5 months of age. Tubular secretory capacity is also limited at birth, approaching adult values by approximately 7 months of age. Published reports describing the pharmacokinetics and pharmacodynamics of commonly used drugs in the neonatal period, as well as differences in drug biodisposition among premature infants, full term neonates, and older infants and children, are reviewed. Our recommendations for neonatal drug therapy are based upon a critical interpretation of these data, an understanding of fetal development and maturational processes, and an understanding of how disease states may affect drug biodisposition in the neonate.

Serum bilirubin levels in Melanesian neonates

The pattern of early neonatal serum bilirubin levels in a population of normal fullterm healthy Melanesian babies was determined. The mean (and standard deviation) of cord blood serum bilirubin from 98 babies was 1.2 (1.4) mg/dl (20.5 (23.9) mumol/l). Between 24 and 60 h of age the mean serum bilirubin from 99 babies was 8 (3.5) mg/dl (136.8 (59.85) mumol/l). Seventeen babies excluded from the main study group because of factors known to predispose to neonatal jaundice had a mean serum bilirubin of 10.7 mg/dl (183 mumol/l). In the early neonatal period, Melanesian babies have a mean serum bilirubin level higher than that reported for Caucasian but lower than that reported for Asian babies. Genetic factors are the most likely explanation for these differences.

Incidence of hyperbilirubinemia in breast- vs. formula-fed infants

A retrospective study of 233 consecutively born full-term infants was performed to determine the effect of several variables on the development of hyperbilirubinemia. Thirty-five (15%) of the infants developed peak bilirubin levels greater than 12 mg/dl in the first week of life. Step-wise multiple regression analysis revealed that breast-feeding was the most predictive of a group of eight variables for the development of hyperbilirubinemia greater than 12 mg/dl. The correlation between type of feeding and hyperbilirubinemia was significant (p less than 0.02). None of the other factors evaluated was significantly associated with hyperbilirubinemia. Breast-fed infants also were found to have a significantly higher incidence of hyperbilirubinemia greater than 15 mg/dl; 12 of 101 (12%) infants compared with 2 of 117 (2%) formula-fed infants (p less than 0.002). This group of infants accounted for the increased incidence of hyperbilirubinemia greater than 12 mg/dl in breast-fed infants. There was no significant correlation between weight loss and development of hyperbilirubinemia in the breast-fed infants.