Pharmacogenomics and renal drug disposition in the newborn

Drug-induced renal damage in preterm neonates: state of the art and methods for early detection

Only a small fraction of drugs widely used in neonatal intensive care units (NICU) are specifically authorized for this population. Even if unlicensed or off-label use is necessary, it is associated with increased adverse drug reactions, which must be carefully weighed against expected benefits. In particular, renal damage is frequent among preterm babies, and is considered a predisposing factor for the development of chronic kidney disease in adulthood. Apart from specific conditions affecting premature neonates (e.g. respiratory distress syndrome, perinatal asphyxia), drugs play an important role in impairing renal function because of well-known nephrotoxicity and/or interaction with renal developmental factors. From a review of the available studies on drug use in NICU patients, we identified and described the most commonly administered drugs that are correlated to renal damage. Early detection of kidney injury is becoming an essential aspects for clinicians because of the limited number of biomarkers applicable in the neonatal population. Postnatal changes of biochemical processes that influence pharmacokinetic and pharmacodynamic aspects need to be further investigated in order to better understand the mechanisms of drug toxicity in this population. The most promising strategies for dose adjustment and therapeutic schemes are discussed. The purpose of this review was to describe current knowledge on drug use among premature babies and their implication in kidney injury development, as well as to highlight available strategies for early detection of renal damage.

Pharmacokinetics in neonatal prescribing: evidence base, paradigms and the future

Paediatric patients, particularly preterm neonates, present many pharmacological challenges. Due to the difficulty in conducting clinical trials in these populations dosing information is often extrapolated from adult populations. As the processes of absorption, distribution, metabolism and excretion of drugs change throughout growth and development extrapolation presents risk of over or underestimating the doses required. Information about the development these processes, particularly drug metabolism pathways, is still limited with weight based dose adjustment presenting the best method of estimating pharmacokinetic changes due to growth and development. New innovations in pharmacokinetic research, such as population pharmacokinetic modelling, present unique opportunities to conduct clinical trials in these populations improving the safety and effectiveness of the drugs used. More research is required into this area to ensure the best outcomes for our most vulnerable patients.

Pharmacogenomics and pharmacoepigenomics in pediatric medicine

In the past several years, human genetics studies have progressed from monogenic to complex and common diseases because of the advancement in technologies. There is increased knowledge of the pharmacokinetics and pharmacogenomics of the drugs in adults as well as in children. These technological developments provided new diagnostic, prognostic, and therapeutic opportunities. We are now in a position to address many additional ambitious questions. For instance, in clinical medicine, interindividual variation in drug response is a major problem. Some of the heterogeneity of drug safety and efficacy among individuals can be explained by pharmacogenomics. It has also the potential to improve the treatment in both adults and children. In pediatrics however, there is ontogeny and metabolic capacity in children is different compared to adults. Several specific developmental changes may underlie some of the variability in drug response seen in children. They may also be responsible for adverse drug reactions (ADRs). Therefore, much of the diversity in drug effects cannot be explained by studying the genomic diversity alone. It is necessary to include the effect of growth (involves variations in gene expression) along with genetic differences when explaining the variability in treatment response. In this respect epigenomics may expand the scope of pharmacogenomics towards optimization of drug therapy. Future studies must focus on periods of maturation of the drug-metabolizing enzymes and polymorphisms in their genes by using candidate gene approach, gene expression analysis, genome-wide haplotype mapping, and proteomics. The integration of genetic data and clinical phenotypes along with the role of other factors is necessary to evaluate both efficacy and ADRs of any drug. It may require extensive genetic epidemiological studies spanning over many years.

Clinical pharmacology of furosemide in neonates: a review

Furosemide is the diuretic most used in newborn infants. It blocks the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb of the loop of Henle increasing urinary excretion of Na⁺ and Cl⁻. This article aimed to review the published data on the clinical pharmacology of furosemide in neonates to provide a critical, comprehensive, authoritative and, updated survey on the metabolism, pharmacokinetics, pharmacodynamics and side-effects of furosemide in neonates. The bibliographic search was performed using PubMed and EMBASE databases as search engines; January 2013 was the cutoff point. Furosemide half-life (t_1/2) is 6 to 20-fold longer, clearance (Cl) is 1.2 to 14-fold smaller and volume of distribution (Vd) is 1.3 to 6-fold larger than the adult values. t_1/2 shortens and Cl increases as the neonatal maturation proceeds. Continuous intravenous infusion of furosemide yields more controlled diuresis than the intermittent intravenous infusion. Furosemide may be administered by inhalation to infants with chronic lung disease to improve pulmonary mechanics. Furosemide stimulates prostaglandin E2 synthesis, a potent dilator of the patent ductus arteriosus, and the administration of furosemide to any preterm infants should be carefully weighed against the risk of precipitation of a symptomatic patent ductus arteriosus. Infants with low birthweight treated with chronic furosemide are at risk for the development of intra-renal calcifications.

Ontogeny and drug metabolism in newborns

In pediatric age and particularly in newborn infants the drug efficacy and safety are influenced by the growth and development on drug Absorption, Distribution, Metabolism and Excretion (ADME). Thanks to the fast development of pharmacogenomics and pharmacogenetics, the drug therapy promises to be adapted to the genetic profile of the individual, reducing considerably the side effects of drugs and increasing their efficacy. Interindividual variability in drug response is well known in both adults and children. Such a variability is multifactorial considering both intrinsic and extrinsic factors. Drug distribution in the neonate is influenced by a variety of age-dependent factors as a total body water content and distribution variations, role of drug transporters, blood/tissue protein binding, blood and tissue pH and perfusion. The development of enzymes involved in human metabolism were classified in 3 categories: 1) those expressed during the whole or part of the fetal period, but silenced or expressed at low levels within 1-2 years after birth; 2) those expressed at relatively constant levels throughout fetal development, but increased to some extent postnatally; and 3) those whose onset of expression can occur in the third trimester, but substantial increase is noted in the first 1-2 years after birth. Besides this intrinsic aspects influencing pharmacokinetics during the neonatal period there are other important events such as inborn or acquired diseases, environment and finally pharmacogenetics and pharmacogenomics. Thousands of deaths every years are caused by fatal drug reactions; among the potential causes there are not only the severity of the disease being treated, drug interactions, nutritional status, renal and liver functions, but also the inherited differences in drug metabolism and genetic polymorphism. Adverse drug reactions (ADRs) among pediatric patients have been shown to be three times more frequent than in adults. On August 2010 The National Institute of Child Health and Human Development (NICHD) addressed patient safety issues in the NICU, recognizing that to understand and prevent adverse events, systematic research and education in safety issues needed. From all these concepts in terms of ADME, pharmacogenetics (relative to a single gene) and pharmacogenomics (relative to many genes) it is becoming more evident the perspective of the new concept of individualized medicine. The goal of this should be to identify which group of patients responds positively, which patients are nonresponders and who experiences adverse reaction for the same drug and dose. The interindividual variability in response to any drug is mostly dependent on DNA sequence variations across the human genome, the haplotype map (HAPMAP). At present there is still a big distance beween the knowledge in genetic and the practical application to model the drug profile to the genetic/genomic profile of the single patient. In the neonatal period the effects of growth in the pharmacodynamic, processes can help optimizing the dosage of neonatal frequently used medicines, thereby, minimizing their toxicity and increasing their efficacy. It should be useful to create accurate dosage adjustments according to the week of development.

Neonatal pharmacology: extensive interindividual variability despite limited size

Providing safe and effective drug therapy to neonates requires knowledge of the impact of development on the pharmacokinetics and pharmacodynamics of drugs. Although maturational changes are observed throughout childhood, they are most prominent during the first year of life. Several of these processes overlap, making development an extremely dynamic system in the newborn compared with that in infants, children, or adults. Changes in body composition and porportions, liver mass, metabolic activity, and renal function collectively affect the pharmacokinetic behavior of medications. Instead of simply adapting doses by scaling adult or pediatric doses on the basis of a patient's weight and/or body surface area, integrated knowledge of clinical maturation and developmental pharmacology is critical to the safe and effective use of medications in neonates. Unfortunately, the effects of human ontogeny on both pharmacokinetics and pharmacodynamics have not been well established in these early stages of life, and information regarding the influence of developmental changes on the pharmacodynamics of medications is even more limited. Theoretically, age-dependent variations in receptor number and affinity for drugs have significant potential to influence an individual's response to drug therapy. In this review, some of the relevant covariates of pharmacokinetics and pharmacodynamics in neonates are reviewed and illustrated based on the published literature.

Mother-infant antidepressant concentrations, maternal depression, and perinatal events

OBJECTIVE

The authors explored the relationship of cord-maternal antidepressant concentration ratios and maternal depression with perinatal events and preterm birth.

METHOD

The investigators examined 21 mother-infant pairs that had antidepressant exposure during pregnancy. The antidepressants included serotonin reuptake inhibitors (SRIs) and nortriptyline (a norepinephrine inhibitor and mild SRI). The mothers were evaluated with the Structured Clinical Interview for DSM-IV. Depression ratings were repeated at 20, 30, and 36 weeks' pregnancy. At delivery, investigators assessed cord and maternal antidepressant concentrations, neonatal outcomes on the Peripartum Events Scale (PES), and gestational weeks at birth. The investigators performed this study at the Women's Behavioral HealthCARE Program, Western Psychiatric Institute and Clinic, University of Pittsburgh Medical Center, Pennsylvania, from April 2003 until September 2006.

RESULTS

Mean ± SD cord-to-maternal concentration ratios were 0.52 ± 0.35 (range, 0.00-1.64) for the parent drug and 0.54 ± 0.17 (range, 0.28-0.79) for the metabolite. Nine of 21 mothers (43%) had a major depressive episode. From examining the maximum depression ratings, the mean ± SD Structured Interview Guide for the Hamilton Depression Rating Scale, Atypical Depression Symptoms Version score was 16.0 ± 7.6. One third (7/21) of infants had at least 1 perinatal event (PES ≥ 1). The frequency of deliveries complicated by any perinatal event was similar in depressed and nondepressed mothers. There was no significant association between perinatal events and cord-to-maternal antidepressant concentration ratios or maternal depression levels. Exposure to short half-life antidepressants compared to fluoxetine resulted in more perinatal events (7/16 = 44% vs 0/5 = 0%; P = .06). Fourteen percent (3/21) of infants were preterm. Preterm birth was not associated with cord-to-maternal metabolite concentration ratios, depression levels, or exposure to fluoxetine.

CONCLUSIONS

Antidepressant-exposed infants experienced a limited number of transient perinatal events. No association between cord-maternal concentration ratios or maternal depression and perinatal events could be identified. Contrary to other reports, we detected no increased risk for perinatal events with fluoxetine therapy compared to the short half-life antidepressants.

TRIAL REGISTRATION

clinicaltrials.gov Identifier: NCT00279370.

Drug transporters and renal drug disposition in the newborn

The individual response to a drug in terms of drug efficacy and toxicity is highly variable; this represents a major problem in clinical practice. Potential causes for such variability include pathogenesis and severity of the disease being treated, drug interactions, patient age, nutritional status, renal and liver function and concomitant illness. Inherited differences in drug metabolism and genetic polymorphism of targets of drug therapy can have even greater influence on the efficacy and toxicity of medications. We will discuss the role of drug transporters (organic anion transporting polypeptides and Pgp), drug-related gene polymorphisms and pathologies, renal function and drug metabolism in a very special patient population, the newborn. Reliable predictions of drug pharmacokinetics in the newborn, derived from an understanding of the transport mechanisms, should allow therapeutic agents to be used more safely in this special population.

Pharmacogenomics: a new paradigm to personalize treatments in nephrology patients

Although notable progress has been made in the therapeutic management of patients with chronic kidney disease in both conservative and renal replacement treatments (dialysis and transplantation), the occurrence of medication-related problems (lack of efficacy, adverse drug reactions) still represents a key clinical issue. Recent evidence suggests that adverse drug reactions are major causes of death and hospital admission in Europe and the United States. The reasons for these conditions are represented by environmental/non-genetic and genetic factors responsible for the great inter-patient variability in drugs metabolism, disposition and therapeutic targets. Over the years several genetic settings have been linked, using pharmacogenetic approaches, to the effects and toxicity of many agents used in clinical nephrology. However, these strategies, analysing single gene or candidate pathways, do not represent the gold standard, being the overall pharmacological effects of medications and not typically monogenic traits. Therefore, to identify multi-genetic influence on drug response, researchers and clinicians from different fields of medicine and pharmacology have started to perform pharmacogenomic studies employing innovative whole genomic high-throughput technologies. However, to date, only few pharmacogenomics reports have been published in nephrology underlying the need to enhance the number of projects and to increase the research budget for this important research field. In the future we would expect that, applying the knowledge about an individual's inherited response to drugs, nephrologists will be able to prescribe medications based on each person's genetic make-up, to monitor carefully the efficacy/toxicity of a given drug and to modify the dosage or number of medications to obtain predefined clinical outcomes.

Developmental pharmacology: neonates are not just small adults

Neonatal drug dosing needs to be based on the physiological characteristics of the newborn and the pharmacokinetic parameters of the drug. Size-related changes can in part be modelled based on allometry and relates to the observation that metabolic rate relates to weight by a kg 0.75 trend. Until adult metabolic activity has been reached, ontogeny, i.e. isoenzyme-specific maturation and maturation of renal clearance also contributes to drug metabolism, making isoenzyme-specific documentation of maturation necessary. Changes in body composition and ontogeny are most prominent in neonates. The body fat content (/kg) is markedly lower and the body water content (/kg) is markedly higher in neonates. These findings have an impact on the distribution volume of both lipophilic and hydrophilic drugs. Drugs are cleared either by metabolism or elimination. While the first is mainly hepatic, the second route is mainly renal. Both hepatic metabolism and renal clearance display maturation in early life although other covariables (e.g. polymorphisms, co-administration of drugs, first pass metabolism, disease characteristics) further contribute to the interindividual variability in drug disposition. Documentation of these maturational processes based on in vivo 'case' studies is of value since these drug-specific observations can subsequently be extrapolated to other drugs which are either already being prescribed or even considered for use in neonates by the introduction of these observations in 'generic physiologically-based pharmacokinetic' models.

Renal drug clearance in preterm neonates: relation to prenatal growth

Aminoglycosides and glycopeptides are almost exclusively eliminated by renal excretion. Postmenstrual age (PMA) is the best predictor of their clearance, presumably because it predicts the time course of development of the glomerular filtration rate (GFR). Intrauterine growth restriction has an impact on the normalized weight of the kidney, on the number of nephrons, on GFR, and on tubular function in human perinatal life. We investigated whether prenatal growth also affects clearance of drugs such as aminoglycosides or glycopeptides that are eliminated through the kidney. Observations collected in two population pharmacokinetic studies involving preterm neonates and investigating amikacin and vancomycin in the first month of postnatal life were used to estimate the impact of prenatal growth (as judged by birth weight for gestational age) on the clearance of these drugs. Data from 1212 drug measurements (vancomycin, 648; amikacin, 564) in 531 subjects (vancomycin, 249; amikacin, 282) were available for study. Neonates born small for gestational age (SGA) were found to have a 16.2% (coefficient of variation, 12.2%) reduction in drug clearance. This effect was present from birth up to the postnatal age of 4 weeks. The covariate size (weight 0.75) explained 47.3% of drug clearance; PMA, 25.2%; coadministration of a nonselective cyclo-oxygenase inhibitor, 3.5%; renal function, 7.6%; and SGA, 1.7%. Renal drug clearance is significantly lower in preterm neonates born SGA than in appropriate-for-gestational-age (AGA) controls. This reduced clearance was observed not only at birth but also up to the postnatal age of 4 weeks.

Evidence of excessive concentrations of 5-flucytosine in children aged below 12 years: a 12-year review of serum concentrations from a UK clinical assay reference laboratory

5-flucytosine (5-FC) is an antifungal drug used for the treatment of serious infections caused by Candida or Cryptococcus spp. In the UK, the recommended pre- and post-dose serum therapeutic ranges are 30-40 mg/L and 70-80 mg/L, respectively. A 12-year retrospective review of serum concentrations of 5-FC in three groups of children aged 1-30 days (n=167), 31-60 days (n=102) and 91 days to 12 years (n=122) was conducted. In these three age groups, 65.1%, 44.4% and 21.3% of pre-dose samples and 39.3%, 29.2% and 19.7% of post-dose samples were above the recommended ranges. Both the mean concentration and the percentage of concentrations above the recommended ranges were significantly higher in the youngest age group (1-30 days old), suggesting that the standard dose of 100 mg/kg daily may not be an appropriate dose in this age group.