Bilirubin-albumin Binding Research Articles

Effect of Cloxacillin on Bilirubin-albumin Binding

Cloxacillin is usually given to newborn infants with sepsis in particular for penicillinase-producing staphylococcus aureus. The effect of cloxacillin on bilirubin-albumin binding was investigated in vitro using the peroxidase oxidation method with human albumin (bilirubin 0.255 mM, albumin 0.45 mM, billalb 0.56, pH 7.4, temperature 3 0°C). Sulfisoxazole, a drug which is capable of displacing bilirubin from albumin was used as control.
 The displacement constant of cloxacillin was 4.86 x 1o5 Nr1, stronger than that of sulfisoxazole (1. 72 x 104 M-1). Both drugs were capable of displacing bilirubin as determined by their maximal displacement factors of 2.21 and 2.29, respectively. Since cloxacillin apparently increases the risk of bilirubin encephalopathy the use of this drug in jaundiced newborns with sepsis, especially in the premature infants, should be reconsidered.

The uncomfortable problem of unbound bilirubin in extremely preterm infants

Unbound, unconjugated bilirubin is neurotoxic and increased levels lead to bilirubin encephalopathy in newborn infants. Clinical evaluation of unbound bilirubin is not typically available and potentially neurotoxic levels must be inferred from the total serum bilirubin level that reflects both albumin-bound unconjugated bilirubin and unbound bilirubin. Inferring safe levels of unbound bilirubin is less reliable in preterm compared with full term infants, and in this volume of The Journal, Amin et al explore this problematic situation. Unbound bilirubin was measured prospectively during the first postnatal week in preterm infants and as expected, infants born at <30 weeks of gestation had reduced bilirubin binding affinity. More unexpectedly, the authors observed an uncoupling of the relationship between unbound bilirubin and total serum bilirubin: even as total serum bilirubin levels decreased, unbound bilirubin continued to rise, potentially increasing the risk of neurotoxicity. The confidence limits for this finding were broad, suggesting considerable individual variation that needs further investigation. This study adds to the uncomfortable problem of jaundice in extremely preterm infants. It is not clear whether neonatologists should have a high level of concern about unbound bilirubin in routine patient care as we seldom identify extremely preterm infants with symptoms of acute bilirubin encephalopathy. We do not know if this is because symptoms rarely occur or if they are just very difficult to identify in this population. The long-term implications have not been evaluated, and the balance of risks and benefits of phototherapy may be more complicated than is currently understood (Clin Perinatol 2016;43:291-5). This study should spur further investigation in many directions with a goal to better understand the causes and effects of unbound hyperbilirubinemia in extremely preterm infants. Article page 47 ▶ Bilirubin Albumin Binding and Unbound Unconjugated Hyperbilirubinemia in Premature InfantsThe Journal of PediatricsVol. 192PreviewTo evaluate the associations between unbound bilirubin (UB) and total serum bilirubin (TSB), bilirubin:albumin molar ratio (BAMR), and bilirubin albumin binding affinity (Ka) as a function of gestational age (GA) in infants born at 24-33 weeks GA. Full-Text PDF

Bilirubin Albumin Binding and Unbound Unconjugated Hyperbilirubinemia in Premature Infants

To evaluate the associations between unbound bilirubin (UB) and total serum bilirubin (TSB), bilirubin:albumin molar ratio (BAMR), and bilirubin albumin binding affinity (Ka) as a function of gestational age (GA) in infants born at 24-33 weeks GA. In a prospective observational study, TSB and UB were measured twice daily at least 8 hours apart during the first postnatal week. Serum albumin was measured to calculate BAMR on each day. The highest UB on each day, corresponding TSB, and serum albumin were used to calculate the Ka on each day. For the 166 infants studied, peak UB significantly correlated with concomitant Ka (r = -0.44, P = .001) but not with concomitant TSB or BAMR after adjusting for GA. On multiple regression analyses, there was a significant association of concomitant Ka (-0.06, 95% CI -0.08 to -0.04, P = .0001), but not concomitant TSB or BAMR with peak UB after controlling for GA, birth weight, race, and sex. GA group was a significant effect modifier for the association between Ka and peak UB (0.03, 95% CI 0.02-0.04, P < .001). Interaction analyses showed the association between concomitant Ka and peak UB was significant for the 24-30 weeks GA group infants, but not for the 301/7-33 weeks GA group infants. Peak UB was primarily associated with a decrease in binding affinity in infants ≤30 weeks GA. Interventions aimed at improving binding affinity may be important in decreasing the risk of bilirubin-induced neurotoxicity.

Editor's Note MS#20162317 El Houchi et al - Neonatal jaundice: more than a number

Severe neonatal jaundice (unconjugated hyperbilirubinemia) may cause permanent brain injury and hearing loss in infants worldwide, including those born in developed countries. Bilirubin neurotoxicity is due to the effects of unbound unconjugated bilirubin in the central nervous system. The risk of kernicterus depends not only on the total serum bilirubin, but also factors such as the bilirubin-albumin binding capacity, prematurity, and other neonatal illnesses. In this volume of The Journal, El Houchi et al describe their use of the Bilirubin Induced Neurologic Dysfunction (BIND) Score to evaluate neurotoxicity in infants with severe hyperbilirubinemia, with the hope of improving our ability to detect infants who require timely exchange transfusions. The BIND score evaluates three aspects of the physical examination including mental status,muscle tone and cry pattern on a 0- to 3-point rating scale. In 220 near-term and full-terminfants admitted to their hospital with severe hyperbilirubinemia, El Houchi et al noted that regardless of the total serum bilirubin, infants with BIND scores of 3-4 or more were at increased risk for persistent neurologic abnormalities at 3-5 months of age. The etiology of jaundice for the infants in this study was not described, and the gestational age of the infants was not precisely known. These two factors suggest that further replication of these findings is needed to understand the usefulness of the BIND score across a variety of at-risk populations. However, in this study, El Houchi et al have shown that serial neurologic examinations are an important and cost-effective adjunct to the total serum bilirubin in the evaluation and management of jaundice that should be useful to pediatricians worldwide. Article page 51 ▶ Prediction of 3- to 5-Month Outcomes from Signs of Acute Bilirubin Toxicity in Newborn InfantsThe Journal of PediatricsVol. 183PreviewTo evaluate the ability of the bilirubin-induced neurologic dysfunction (BIND) score to predict residual neurologic and auditory disability and to document the relationship of BIND score to total serum bilirubin (TSB) concentration. Full-Text PDF

The Biological Effects of Bilirubin Photoisomers.

Although phototherapy was introduced as early as 1950’s, the potential biological effects of bilirubin photoisomers (PI) generated during phototherapy remain unclear. The aim of our study was to isolate bilirubin PI in their pure forms and to assess their biological effects in vitro. The three major bilirubin PI (ZE- and EZ-bilirubin and Z-lumirubin) were prepared by photo-irradiation of unconjugated bilirubin. The individual photoproducts were chromatographically separated (TLC, HPLC), and their identities verified by mass spectrometry. The role of Z-lumirubin (the principle bilirubin PI) on the dissociation of bilirubin from albumin was tested by several methods: peroxidase, fluorescence quenching, and circular dichroism. The biological effects of major bilirubin PI (cell viability, expression of selected genes, cell cycle progression) were tested on the SH-SY5Y human neuroblastoma cell line. Lumirubin was found to have a binding site on human serum albumin, in the subdomain IB (or at a close distance to it); and thus, different from that of bilirubin. Its binding constant to albumin was much lower when compared with bilirubin, and lumirubin did not affect the level of unbound bilirubin (Bf). Compared to unconjugated bilirubin, bilirubin PI did not have any effect on either SH-SY5Y cell viability, the expression of genes involved in bilirubin metabolism or cell cycle progression, nor in modulation of the cell cycle phase. The principle bilirubin PI do not interfere with bilirubin albumin binding, and do not exert any toxic effect on human neuroblastoma cells.

Raltegravir In Vitro Effect on Bilirubin Binding

Drugs that displace bilirubin from albumin may increase the risk of kernicterus in neonates. We evaluated the effect of raltegravir on bilirubin-albumin binding in pooled neonatal serum using the peroxidase method. Raltegravir had minimal effect on bilirubin-albumin binding at concentrations of 5 and 10 µM, caused a small but statistically significant increase in unbound bilirubin at 100 µM and caused potentially harmful increases at 500 and 1000 µM. Our data suggest that the effect of raltegravir on neonatal bilirubin binding is unlikely to be clinically significant at typical peak concentrations reached with usual dosing.

Effect of ibuprofen on bilirubin-albumin binding affinity in premature infants

To evaluate the effect of ibuprofen on bilirubin-albumin binding affinity and unbound bilirubin in premature infants. A prospective study with subjects serving as their own controls was performed on <30 weeks' gestational age infants with unconjugated hyperbilirubinemia and who received ibuprofen for patent ductus arteriosus. Infants with congenital malformation, TORCH infections, and conjugated hyperbilirubinemia were excluded. Total serum bilirubin (TSB) and unbound bilirubin (modified peroxidase test) were measured prior to (baseline) and after (follow-up) initiation of ibuprofen. The bilirubin/albumin equilibrium association binding constant was calculated using albumin, TSB, and unbound bilirubin. Ten infants were studied. The mean TSB between baseline (5.9±1.7 mg/dL) was higher than that at follow-up [4.9±1.7 mg/dL]. Mean unbound bilirubin at baseline (0.75±0.65 μg/dL) was similar to that at follow-up (0.63±0.46 μg/dL). No difference existed between mean baseline binding constant (49±50 L/μmol) and that at follow-up (44±36 L/μmol). The ratio of unbound bilirubin with and without ibuprofen, index of displacing effect, was 0.88 (95% CI 0.63-1.14). Ibuprofen may not be associated with bilirubin displacing effect in relatively stable premature infants with mild to moderate unconjugated hyperbilirubinemia.

Cucurbitacin E, a tetracyclic triterpenes compound from Chinese medicine, inhibits tumor angiogenesis through VEGFR2-mediated Jak2-STAT3 signaling pathway

Cucurbitacin E (CuE, α-elaterin), a tetracyclic triterpenes compound from folk traditional Chinese medicine plants, has been shown to inhibit cancer cell growth, inflammatory response and bilirubin-albumin binding. However, the effects of CuE on tumor angiogenesis and its potential molecular mechanism are still unknown. Here, we demonstrated that CuE significantly inhibited human umbilical vascular endothelial cell (HUVEC) proliferation, migration and tubulogenesis in vitro and blocked angiogenesis in chick embryo chorioallantoic membrane assay and mouse corneal angiogenesis model in vivo. Furthermore, we found that CuE remarkably induced HUVEC apoptosis, inhibited tumor angiogenesis and suppressed human prostate tumor growth in xenograft tumor model. Finally, we showed that CuE blocked vascular endothelial growth factor receptor (VEGFR) 2-mediated Janus kinase (Jak) 2-signal transducer and activator of transcription (STAT) 3 signaling pathway in endothelial cells and suppressed the downstream protein kinases, such as extracellular signal-regulated kinase and p38 mitogen-activated protein kinases. Therefore, our studies provided the first evidence that CuE inhibited tumor angiogenesis by inhibiting VEGFR2-mediated Jak-STAT3 and mitogen-activated protein kinases signaling pathways and CuE is a potential candidate in angiogenesis-related disease therapy.

Effect of Free Fatty Acids on Bilirubin–Albumin Binding Affinity and Unbound Bilirubin in Premature Infants

The author has previously shown that intravenous lipid intake may be associated with an increase in unbound bilirubin in infants < or =28 weeks gestational age. The objective of this study was to evaluate whether this increase in unbound bilirubin is mediated by free fatty acids and to examine the secondary effect of free fatty acids on bilirubin-albumin binding affinity. A prospective study was conducted to include 26 infants < or =32 weeks gestational age with indirect hyperbilirubinemia and receiving intravenous lipids during the first 10 postnatal days. Blood samples were collected for unbound bilirubin, binding affinity, and free fatty acid measurement at varying intravenous lipid intakes (1-3 g/kg/d). Regression analyses were performed to evaluate the roles of free fatty acids and binding affinity as mediators. Intravenous lipid intake was significantly associated with an increase in free fatty acids and unbound bilirubin in infants < or =28 weeks but not >28 weeks gestational age. In infants < or =28 weeks gestational age, each unit increase in free fatty acids was significantly associated with a decrease in binding affinity, which was significantly associated with an increase in unbound bilirubin. In infants < or =28 weeks gestational age, intravenous lipid intake may be associated with an increase in unbound bilirubin, and this is mediated by an increase in free fatty acids and a secondary decrease in binding affinity. In infants >28 weeks gestational age, higher intravenous lipid intake may be used because it is unassociated with increases in free fatty acids and unbound bilirubin.

Effect of ibuprofen on bilirubin–albumin binding in vitro at concentrations observed during treatment of patent ductus arteriosus

Background In vitro studies have shown that ibuprofen (IBU) may interfere with bilirubin–albumin binding at concentrations of 100 µg/mL and above. Objectives The present study evaluates the in vitro bilirubin displacement over the range of IBU plasma concentrations observed in vivo during curative treatment of patent ductus arteriosus in preterm infants. Methods Considering that individual plasma concentrations obtained during the clinical development of IBU in preterm infants were ranging between 10 and 70 µg/mL and exceptionally above 100 µg/mL, we used the modified peroxidase method to determine total and unbound bilirubin concentrations without IBU and with IBU over this specific concentration range. Results Total bilirubin and albumin concentrations were respectively 6.6 mg/dL and 2.87 g/dL in pooled newborn plasma. No displacement of bilirubin from its albumin binding sites by IBU was observed over a range of concentrations from 10 to 100 µg/mL. Only a concentration of 200 µg/mL significantly increased the unbound bilirubin by 1.5-fold ( p = 0.0008). Conclusions This in vitro study confirms displacement of bilirubin by a high IBU concentration of 200 µg/mL, however it retrieves no significant displacement over a range of concentrations up to and including 100 µg/mL, i.e. within the range of in vivo concentrations at the recommended dose regimen.

Intravenous Lipid and Bilirubin-Albumin Binding Variables in Premature Infants

The lipid intake at which a significant bilirubin-displacing effect occurs as a function of gestational age (GA) is unclear. To determine the effect of gradual increase in IL intake from 1.5 to 3 g/kg per day on bilirubin-albumin binding variables as a function of GA in premature infants with indirect hyperbilirubinemia. Infants of 24 to 33 weeks' gestation at birth who received IL (20% Intralipid [Fresenius Kabi, Uppsala, Sweden]) doses of 1.5, 2, 2.5, and 3 g/kg per day over 4 consecutive days were prospectively evaluated. The blood samples were drawn twice at least 8 hours apart on each IL intake to measure total serum bilirubin and free bilirubin by the peroxidase test. The highest free bilirubin on each IL intake, the corresponding total serum bilirubin, and serum albumin were used to calculate the bilirubin/albumin binding constant or binding affinity. Sixty-two infants (median GA: 28 weeks) were studied during the first 10 days of life. None of the subjects had culture-proven sepsis, had triglyceride levels of >2.05 mmol/L, or were receiving steroids. Infants were grouped in 2-week GA intervals. The cumulative frequency of elevated free bilirubin concentration (>or=90th percentile or B(f) >or= 32 nmol/L) as a function of IL intake was inversely related to GA and was significantly different among 2-week GA groups. There was significant decrease in binding affinity and increase in free bilirubin concentration with higher IL intake for <or=28 week but not for >28 week GA groups. The IL intake may be associated with a significant fall in the binding affinity of bilirubin for plasma protein and a concomitant increase in free bilirubin concentration in premature infants. The lipid intake at which this occurs depends on GA.

Ibuprofen Augments Bilirubin Toxicity in Rat Cortical Neuronal Culture

Premature infants are at risk for bilirubin-associated brain damage. In cell cultures bilirubin causes neuronal apoptosis and necrosis. Ibuprofen is used to close the ductus arteriosus, and is often given when hyperbilirubinemia is at its maximum. Ibuprofen is known to interfere with bilirubin-albumin binding. We hypothesized that bilirubin toxicity to cultured rat embryonic cortical neurons is augmented by coincubation with ibuprofen. Incubation with ibuprofen above a concentration of 125 microg/mL reduced cell viability, measured by methylthiazole tetrazolium reduction, to 68% of controls (p < 0.05). Lactate dehydrogenase (LDH) release increased from 29 to 38% (p < 0.01). The vehicle solution did not affect cell viability. Coincubation with 10 microM unconjugated bilirubin (UCB)/human serum albumin in a molar ratio of 3:1 and 250 microg/mL ibuprofen caused additional loss of cell viability and increased LDH release (p < 0.01), DNA fragmentation, and activated caspase-3. Preincubation with the pan-caspase inhibitor z-val-ala-asp-fluoromethyl ketone abolished ibuprofen- and UCB-induced DNA fragmentation. The study demonstrates that bilirubin in low concentration of 10 microM reduces neuron viability and ibuprofen increases this effect. Apoptosis is the underlying cell death mechanism.

Calculated free bilirubin levels and neurotoxicity

Although most bilirubin in the circulation is bound to albumin, a relatively small fraction remains unbound. The concentration of this 'free' bilirubin (B(F)) is believed to dictate the biologic effects of bilirubin in jaundiced newborns, including its neurotoxicity. The threshold at which B(F) produces changes in cellular function culminating in permanent cell injury and cell death has been the subject of considerable debate. The objective of this study was to compare calculated central nervous system (CNS) B(F) levels in Gunn rat pups during (i) peak postnatal hyperbilirubinemia and (ii) sulfadimethoxine-induced acute bilirubin encephalopathy (ABE) previously reported from our laboratory with those predicted in human neonates with peak total serum bilirubin (TSB) levels of 35 mg per 100 ml (599 micromol l(-1)), a clinical cohort that often evidence moderate-to-severe adverse post-icteric neurodevelopmental sequelae. Homozygous j/j Gunn rat pups with neonatal hyperbilirubinemia due to a deficiency of the bilirubin conjugating enzyme uridine-diphosphate-glucuronosyl transferase 1A1 were studied along with non-jaundiced littermate heterozygous J/j controls. Sulfadimethoxine was used to displace bilirubin from albumin in hyperbilirubinemic j/j Gunn rat pups to increase their brain bilirubin content and induce ABE. Calculated Gunn rat CNS B(F) levels were determined as a function of genotype, sulfadimethoxine exposure and albumin-bilirubin binding constant. These data were compared with the human CNS B(F) predicted from the calculated serum B(F) in human neonates with a TSB of 35 mg per 100 ml as a function of albumin-bilirubin binding constant, albumin concentration and the assumption that at this hazardous bilirubin level there may be rapid equilibration of B(F) between serum and brain. There was a large gap between the upper limit of the calculated CNS B(F) 95% confidence interval (CI) range in non-jaundiced J/j pups (for example, 112 nM at k=9.2 l micromol(-1)) and the lower limit seen in the saline-treated hyperbilirubinemic j/j pups (556 nM at k=9.2 l micromol(-1)) as well as between the upper limit in saline-treated hyperbilirubinemic j/j pups (1110 nM at k=9.2 l micromol(-1)) and the lower limit seen in sulfadimethoxine-treated jaundiced j/j littermates (3461 nM at k=9.2 l micromol(-1)). There was considerable overlap and remarkable similarity between the predicted human CNS B(F) values at a TSB of 35 mg per 100 ml for a range of reported human serum bilirubin-albumin binding constants and albumin concentrations, and those calculated for saline-treated hyperbilirubinemic j/j Gunn rat pups. This exercise yielded strikingly similar apparent calculated neurotoxic B(F) levels for Gunn rat pups and human neonates rather than orders of magnitude differences that might have been predicted at the outset and add to a growing literature aimed at defining clinically germane neurotoxic B(F) thresholds.Journal of Perinatology (2009) 29, S14-S19; doi:10.1038/jp.2008.218.

Effect of ibuprofen L-lysinate on bilirubin binding to albumin as measured by saturation index and horseradish peroxidase assays

To demonstrate, in vitro, the influence of increasing ibuprofen (IBU) concentration on bilirubin-albumin (B-A) binding. The influence of IBU on B-A binding was measured by saturation index and horseradish peroxidase assays. B-A solutions were prepared at B:A ratios of 0.5, 1.0, 1.5 and 2.0 and bilirubin concentrations of 5 and 10 mg per 100 ml. Drug concentrations used were 142.5, 200 and 285 mg l(-1) for IBU and 100 and 200 mg l(-1) for acetyl salicylic acid (ASA). Similar tests were performed on premature newborn sera with bilirubin concentrations of 5 to 10 mg per 100 ml. By the saturation index test, significant displacement of bilirubin from albumin with IBU was demonstrated only on B-A solution with high B:A ratio of 2.0 and IBU concentration of 285 mg l(-1) and was less as compared to ASA. No displacement was observed in the sera of jaundiced neonates. By the horseradish peroxidase assay using B-A solutions, free bilirubin was significantly increased at (1) increasing concentrations of bilirubin in solution and (2) increasing B:A ratios in a solution containing 5 mg per 100 ml of bilirubin. In the sera of jaundiced neonates, significantly higher free bilirubin concentrations were observed when IBU was added to serum with bilirubin concentration of 10 mg per 100 ml as compared to 5 mg per 100 ml (0.062+/-0.004 versus 0.026+/-0.005, P<0.001 by Student's t-test). Displacement of bilirubin was demonstrated only at high IBU concentration and high B:A ratio. However, free bilirubin levels were not shown to increase with increasing IBU concentration.

Bilirubin-albumin binding capacity in term and preterm infants

Background The risk of kernicterus remains a problem injaundiced newborn especially in low birth weight infants.Kernicterus can develop at low bilirubin levels. Bilirubin-albuminbinding plays an important role in its pathogenesis. Bilirubinalbumin binding concentration can also be used as the cut-offpoint in the administration of phototeraphy.Objective To determine the pattern of albumin bindingconcentration in serum model in vitro and in serum of prematureand term newborn infants from cord blood sample.Methods This study was conducted in Installation of Maternal-Perinatal Dr. Sardjito Hospital from August-September 2004.Blood cord samples from 20 term and 17 preterm infants wereanalysed. Total bilirubin was measured spectrophotometrically andunbound bilirubin concentration was determined by horseradishperoxidase oxidation using UB-analyzer apparatus micromethod.Student t test and linear regression analysis were performed.Results Bilirubin-albumin binding capacity of term infants showeda statistically significant difference compared to that of prematureinfants (18.9±2.1 mg/dl vs 10.2±3.6 mg/dl, P&lt;0.001). This cut-off level approximately reflected a value of unbound bilirubin of1 mg/dl in term and 0.5 mg/dl in premature infants.Conclusions There is a different pattern of bilirubin-albuminbinding capacity between term and preterm infants which is higherin term infants. Bilirubin level of 19 mg/dl and 10 mg/dl in termand preterm newborn, respectively, can be used as cut-off pointto perform more aggressive intervention, such as phototeraphy,and to lower the risk of kernicterus.

Effect of cucurbitacins on bilirubin–albumin binding in human plasma

The aim of this study is to investigate the effect of three cucurbitacins (Cuc) E, D and I on the bilirubin–albumin binding, both in human serum albumin (HSA) and in plasma. Bilirubin–HSA solution and plasma free of cucurbitacins were prepared as well as others containing serial concentrations of cucurbitacins. The concentration of unbound bilirubin was determined in bilirubin–HSA solution and the direct and total bilirubin concentrations were measured in plasma (with normal or elevated bilirubinemia) by Jendrassik and Grof method. In the conditions we adopted Cuc E and D (to a lesser extent), decreased the levels of unbound bilirubin in bilirubin–HSA solution and decreased direct bilirubin concentration and total bilirubin concentration in plasma in a dose-dependent manner while Cuc I had no effect. The effect of Cuc is related to the presence of native HSA. Thus, when albumin was absent or has been denatured by heating or by urea, Cuc E did not modify bilirubin levels, suggesting that the native structure of albumin is essential for such activity. The interaction of HSA with Cuc E was investigated by fluorescence spectroscopy. Cuc E increased the intrinsic fluorescence of the protein and the magnitude of fluorescence intensity of bilirubin–albumin complex. We concluded that Cuc E and D produced a rearrangement in the structure of albumin, particularly in the domain-II, resulting in an increase in the binding of bilirubin to albumin regardless to whether it's conjugated to glucuronic acid or unconjugated.

A Modeling Study of Bilirubin Kinetics During Molecular Adsorbent Recirculating System Sessions

This work presents a quantitative description, by means of a mathematical model, of bilirubin removal during Molecular Adsorbent Recirculating System sessions. The model includes four compartments: two for the patient, and two for the albumin circuit. Equations in each compartment express mass preservation, mass exchange between compartments, and bilirubin-albumin binding kinetics. Model development and validation are based on in vivo data of bilirubin concentration acquired in eight sessions at different times during the session. The accuracy of the model in reproducing real data is high (error in blood = -0.3 +/- 0.93 mg/dL), if three parameters, representing the depurative efficacy of the system (the dialysance of the blood filter and the initial and final clearance of the depurative elements in the albumin circuit), are estimated on each single session. However, model accuracy is only slightly deteriorated (error in blood = -0.4 +/- 0.99 mg/dL) if a single set of parameters (fixing the three parameters at their mean values) is adopted. These results suggest that the model may be used a priori (i.e., using a single set of parameters) to achieve a satisfactory prediction of the overall bilirubin removal, as well as a posteriori for the estimation of device parameters. The latter use may allow the investigation of the dependence of these parameters on the operative and clinical conditions, in the effort to arrive at a rationalization and optimization of the treatment.

Effect of ibuprofen on bilirubin-albumin binding

Ibuprofen is used for closing the ductus arteriosus in premature newborn infants. Ibuprofen interferes with bilirubin-albumin binding and increases the unbound bilirubin in pooled newborn plasma to levels similar to those produced by sulfisoxazole, a drug that causes kernicterus in premature newborn infants.

Unbound Bilirubin in a Term Newborn With Kernicterus

In premature newborns, bilirubin-induced changes in the auditory brainstem response (ABR) begin at unbound (nonalbumin-bound or “free”) bilirubin levels above .5 μg/dL,1 and kernicterus becomes likely at levels between ∼1 and 1.5 μg/dL (.017-.026 μmol/L).2,3 In term newborns, however, unbound bilirubin levels between .9 and 2 μg/dL, which would be associated kernicterus in premature newborns, produce only subtle, reversible changes in ABR wave latency and amplitude.4 Although the unbound bilirubin levels associated with kernicterus in term newborns are unknown, they clearly are greater than the levels associated with kernicterus in premature infants. This indicates that, as with the total bilirubin and total bilirubin/albumin ratio, the unbound bilirubin levels associated with kernicterus increase as birth weight and gestation increase.1,5 We have been using a Food & Drug Administration-approved method6 for measuring unbound bilirubin in jaundiced newborns as an adjunct to their clinical care since 1998. We use a weight-based unbound bilirubin reference value of 1.3 μg/dL/kg (the level of unbound bilirubin at which exchange transfusion should be considered) up to a maximum of 4 μg/dL to accommodate the need to increase the reference unbound bilirubin as birth weight increases and to incorporate the solubility limits of unbound bilirubin at ph 7.4 (∼4 μg/dL) into the reference criteria.1–5,7–9 We recently encountered a term, jaundiced newborn that developed acute shock and died, apparently from kernicterus. This report describes the infant’s clinical course and bilirubin-albumin binding data. This case provides insight into the levels of unbound bilirubin associated with kernicterus in term infants as well as the acute changes in distribution of the bilirubin load (miscible bilirubin pool) between the tissues and the vascular space following the onset of kernicterus. A 110-hour-old (4.5-day-old) Nigerian male newborn presented to … Reprint requests to (C.E.A.) Division of Neonatology, Department of Pediatrics, California Pacific Medical Center, 3850 California St, San Francisco, CA 94118. E-mail: ligand{at}centurytel.net

Reply. Ibuprofen for closure of patent ductus arteriosus: is it really safe in hyperbilirubinaemic infants?

Sir: The safety and efficacy of ibuprofen versus indomethacin for the treatment of patent ductus arteriosus (PDA) in premature infants has been investigated in at least five randomised trials, with a view to describing the different cerebral, renal and mesenteric effects of both drugs [2, 4, 5, 6, 7]. It has already been well demonstrated that ibuprofen does not reduce cerebral, renal or mesenteric blood flow by comparison with indomethacin, and that it has fewer short-term side-effects. An important next step would be to study the longterm effects of ibuprofen versus indomethacin for PDA closure. The purported effect of ibuprofen on the displacement of bilirubin from albumin [1], which would increase the risk of kernicterus, needs to be evaluated in a clinical randomised controlled trial. Moreover, although proof that indomethacin has no significant effects on bilirubin-albumin binding at therapeutic concentrations has already emerged from an ‘‘in vitro’’ study [3], it is important to bear in mind that the conditions may be different in sick preterm infants. It is only by conducting adequate randomised controlled trials studying the long-term effects of ibuprofen versus indomethacin for PDA closure will we be able to settle our doubts. References