Individualized dosing of aminoglycosides in neonates: mission accomplished or work in progress?

Cytochrome P450 genetic polymorphism in neonatal drug metabolism: role and practical consequences towards a new drug culture in neonatology

The cytochrome P450 superfamily (CYP450) in humans is formed by 57 functional monooxygenases critical for the metabolism of numerous endogenous and exogenous compounds. The superfamily is organized into 18 families and 44 subfamilies. CYP nomenclature is based on the identity of amino acids. The most important functions of the CYP450 are related to metabolism of endogenous compounds, detoxification of exogenous xenobiotics and decomposition of the vast majority of currently used drugs. The expression of CYP450 enzymes in the human body is characterized by a marked substrate and tissue specificity, the most important being localized in the liver, but also present in kidney, lung, brain, breast, prostate and in the small intestine. The human cytochrome P450 3A gene family (CYP3A) accounts for the largest portion of CYP450 proteins in human liver and includes 4 genes: CYP3A4, CYP3A5, CYP3A7, CYP3A43. Multiple and complex genetic variations, marked interindividual, interethnic and gender variability have been reported regarding CYP3A isoform expression and activity. Multiple factors may affect CYP3A expression and activity, such as inducers like rifampicin, phenobarbital, 3-methylcholantrene, beta-naphtoflavone, and dexamethasone. The maturation of organ systems, paralleled by ontogeny of drug-metabolizing enzymes during fetal life and in the first months of postnatal life, surely exerts profound effects on drug disposition, probably being the predominant factor accounting for age-associated changes in drug clearance. In fact, drug dosage in the perinatal period represents a continuous challenge for neonatologists. The purpose of this article is to provide a brief review of the pharmacokinetic differences between neonates and adults, showing the peculiarities of liver CYP450-related drug metabolism in the perinatal period and at birth, and to report the toxic mechanisms of liver injury in neonates, due to the most frequently utilized drugs in NICU centers.

Educational paper: do we need neonatal clinical pharmacologists?

Effective and safe drug administration in young infants should be based on integrated knowledge concerning the evolving physiological characteristics of the infant who will receive the drug and the pharmacokinetic and pharmacodynamic characteristics of a given drug. Consequently, clinical pharmacology in neonates is as dynamic and diverse as the neonates we are entitled to take care of. Even more than median estimates, covariates of variability within the population are of clinical relevance. We aim to illustrate the complexity and the need for neonatal clinical pharmacology based on the gap between current and likely best clinical practice for two commonly administered compounds (aminoglycosides for infection and ibuprofen for patent ductus arteriosus) and one new compound (bevacizumab, to treat threshold retinopathy of prematurity). Progression has been made to render pharmacokinetic studies child size, e.g., low volume samples, optimal study design, and population pharmacokinetics. Challenges to further improve clinical pharmacology in neonates include, when appropriate, the validation of off-patent drug dosing regimens and of infant-tailored formulations. Knowledge integration, i.e., the use of available data to improve current drug use and to predict pharmacokinetics/pharmacodynamics for similar compounds is needed. Development of clinical research networks is helpful to achieve these goals.

Creatinine reference values in ELBW infants: impact of quantification by Jaffe or enzymatic method

OBJECTIVE

Serum creatinine (Scr) reflects to a certain extent glomerular filtration rate in neonates, but postnatal observations also depends on the technique used to quantify Scr (Jaffe colorimetry or enzymatic quantification).

METHODS

In an attempt to quantify differences between these techniques, we compared postnatal Scr trends in two consecutive cohorts of extremely low birth-weight (ELBW) neonates before and following a switch from uncompensated Jaffe to enzymatic Scr quantification. Postnatal Scr (Days 1, 2, 3, 4, 5, 6, 7, 8, 9, 14, 21, 28, and 42) in 151 ELBW neonates (uncompensated Jaffe) was compared to 116 more recently admitted ELBW neonates (enzymatic).

RESULTS

Although clinical characteristics were similar between both cohorts, median postnatal Jaffe Scr values were significantly higher compared to enzymatic quantification (all days, at least p < 0.001) throughout postnatal life. While both cohorts displayed a similar trend with an initial increase with a Scr peak on Days 3 and 4 and a subsequent decrease, the difference in within-day median values fluctuated between 11 and 24 mmol.L(-1). There is neither fixed nor relative difference in Scr between both techniques.

CONCLUSIONS

When using Scr to estimate renal function in ELBW neonates, clinicians should in addition to the postnatal changes and other covariates of renal function, also consider the technique applied. We provide reference values and comparison between both techniques.

Postnatal trends in creatinemia and its covariates in extremely low birth weight (ELBW) neonates

To document trends and covariates of creatinemia (Scr) in extremely low birth weight (ELBW, < 1,000 g) neonates, maternal characteristics [betamethasone, premature preterm rupture of membranes (PPROM), pre-eclampsia, maternal Scr], characteristics at delivery [gestational age (GA), birth weight (BW), small for GA (SGA), Apgar, intubation] and during neonatal stay [ventilation, oxygen, parenteral nutrition, ibuprofen, steroids, intraventricular hemorrhage, retinopathy of prematurity (ROP), phototherapy] were linked with Scr observations. Data were reported by median and range or incidence. Characteristics in ELBW neonates with raised peak Scr (>P75) were compared to controls (<P75). In 151 ELBW neonates, an initial increase in Scr was observed, resulting in a peak Scr on day 3 or 4 of 99.9 (46.8-221.8) μmol/l with subsequent decrease. In cases (n  = 37) with a peak Scr >P75 (112.3 μmol/l), Scr remained elevated until day 28. Mothers of cases received less betamethasone, neonates had a lower GA, lower BW, lower Apgar, and needed more often intubation. Postnatal ventilation, oxygen, parenteral nutrition, ibuprofen, steroids, ROP, and intraventricular hemorrhage were different. GA and ventilation or Apgar were independent factors for raised peak Scr. ELBW neonates display trends similar to heavier neonates, but peak Scr is higher, and the subsequent decrease slower. Raised creatinemia in ELBW neonates reflects immaturity (GA) and morbidity (ventilation, Apgar).

Creatinaemia at birth is equal to maternal creatinaemia at delivery: does this paradigm still hold?

OBJECTIVE

The paradigm that creatinaemia at birth is equal to maternal creatinaemia may also depend upon the quantification technique applied. Paired maternal-neonatal creatinaemia samples in whom Jaffe in both or compensated Jaffe (maternal) and enzymatic quantification (neonate) were applied.

METHODS

Extreme low birth weight infants in two time intervals were included when paired maternal-neonatal creatinaemia samples were available. In cohort 1 (2000-2005), creatinaemia (mothers and neonates) was based on Jaffe assay. In cohort 2 (2007-2010), maternal creatinaemia was based on compensated Jaffe. In neonates, an enzymatic technique was applied. Unpaired Mann Whitney U, paired Wilcoxon and Bland-Altman were used.

RESULTS

Based on 80 and 52 paired creatinaemia samples, there was no significant difference between maternal (0.80, 0.41-1.6 mg.dl(-1)) and neonatal creatinaemia (0.78, 0.31-1.46 mg.dl(-1)) in cohort 1 while a significant difference (p < 0.001) between maternal (0.6, 0.29-2.24 mg.dl(-1)) and neonatal creatinaemia (0.67, 0.4-2.2 mg.dl(-1)) was observed for cohort 2. Using Bland-Altman, the fit was perfect for cohort 1 (mean diff -0.02 mg.dl(-1)), but not for cohort 2 (-0.08 mg.dl(-1)).

CONCLUSIONS

The quantification method affects the paradigm that creatinaemia at birth is similar to maternal creatinaemia. Maternal and neonatal creatinaemia values depend on the method used. Consequently, method-specific reference values are needed.