Intravenous indometacin in preterm infants with symptomatic patent ductus arteriosus. A population pharmacokinetic study

Developmental pharmacokinetics of indomethacin in preterm neonates: Severely decreased drug clearance in the first week of life

Indomethacin is used commonly in preterm neonates for the prevention of intracranial hemorrhage and closure of an abnormally open cardiac vessel. Due to biomedical advances, the infants who receive this drug in the neonatal intensive care unit setting have become younger, smaller, and less mature (more preterm) at the time of treatment. To develop a pharmacokinetics (PK) model to aid future dosing, we designed a prospective cohort study to characterize indomethacin PK in a dynamically changing patient population. A population PK base model was created using NONMEM, and a covariate model was developed in a primary development cohort and subsequently was tested for accuracy in a validation cohort. Postnatal age was a significant covariate for hepatic clearance (CL_H ) and renal clearance (CL_R ). The typical value of the total clearance (CL, the sum of CL_R and CL_H ) was 3.09 ml/h and expressed as CL/WT_median  = 3.96 ml/h/kg, where WT_median is the median body weight. The intersubject variability of CL_R and CL_H were 61% and 207%, respectively. The typical value of the volume of distribution V_p  = 366 ml (V_p /WT_median  = 470 ml/kg), and its intersubject variability was 38.8%. Half-life was 82.1 h. Compared with more mature and older preterm populations studied previously, indomethacin CL is considerably lower in this contemporary population. Model-informed precision dosing incorporating important covariates other than weight alone offers an opportunity to individualize dosing in a susceptible patient undergoing rapid change.

Patent Ductus Arteriosus: A Contemporary Perspective for the Pediatric and Adult Cardiac Care Provider

The burden of patent ductus arteriosus (PDA) continues to be significant. In view of marked differences in preterm infants versus more mature, term counterparts (viewed on a continuum with adolescent and adult patients), mechanisms regulating ductal patency, genetic contributions, clinical consequences, and diagnostic and treatment thresholds are discussed separately, when appropriate. Among both preterm infants and older children and adults, a range of hemodynamic profiles highlighting the markedly variable consequences of the PDA are provided. In most contemporary settings, transcatheter closure is preferable over surgical ligation, but data on longer-term outcomes, particularly among preterm infants, are lacking. The present review provides recommendations to identify gaps in PDA diagnosis, management, and treatment on which subsequent research can be developed. Ultimately, the combination of refined diagnostic thresholds and expanded treatment options provides the best opportunities to address the burden of PDA. Although fundamental gaps remain unanswered, the present review provides pediatric and adult cardiac care providers with a contemporary framework in PDA care to support the practice of evidence-based medicine.

Genetics of the patent ductus arteriosus (PDA) and pharmacogenetics of PDA treatment

Patent ductus arteriosus (PDA) is a frequent, complex, and difficult to treat clinical syndrome among preterm infants in the neonatal intensive care unit. In addition to known clinical risk factors, there are emerging data about genetic predisposition to PDA in both animal and human models. Clinical response and toxicity from drugs used to treat PDA are highly variable. Developmental and genetic aspects of pharmacokinetics and pharmacodynamics influence exposure and response to pharmacologic therapies. Given the variable efficacy and toxicity of known drug therapies, novel therapeutic targets for PDA treatment offer the promise of precision medicine. This review addresses the known genetic contributions to prolonged ductal patency, variability in response to drug therapy for PDA, and potential novel drug targets for future PDA treatment discovery.

Population Pharmacokinetics of Trimethoprim-Sulfamethoxazole in Infants and Children

Trimethoprim (TMP)-sulfamethoxazole (SMX) is used to treat various types of infections, including community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) and Pneumocystis jirovecii infections in children. Pharmacokinetic (PK) data for infants and children are limited, and the optimal dosing is not known. We performed a multicenter, prospective PK study of TMP-SMX in infants and children. Separate population PK models were developed for TMP and SMX administered by the enteral route using nonlinear mixed-effects modeling. Optimal dosing was determined on the basis of the matching adult TMP exposure and attainment of the surrogate pharmacodynamic (PD) target for efficacy, a free TMP concentration above the MIC over 50% of the dosing interval. Data for a total of 153 subjects (240 samples for PK analysis) with a median postnatal age of 8 years (range, 0.1 to 20 years) contributed to the analysis for both drugs. A one-compartment model with first-order absorption and elimination characterized the TMP and SMX PK data well. Weight was included in the base model for clearance (CL/F) and volume of distribution (V/F). Both TMP and SMX CL/F increased with age. In addition, TMP and SMX CL/F were inversely related to the serum creatinine and albumin concentrations, respectively. The exposure achieved in children after oral administration of TMP-SMX at 8/40 mg/kg of body weight/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 320/1,600 mg/day divided into administration every 12 h and achieved the PD target for bacteria with an MIC of 0.5 mg/liter in >90% of infants and children. The exposure achieved in children after oral administration of TMP-SMX at 12/60 and 15/75 mg/kg/day divided into administration every 12 h matched the exposure achieved in adults after administration of TMP-SMX at 640/3,200 mg/day divided into administration every 12 h in subjects 6 to <21 years and 0 to <6 years of age, respectively, and was optimal for bacteria with an MIC of up to 1 mg/liter.

Polymorphisms in CYP2C9 are associated with response to indomethacin among neonates with patent ductus arteriosus

BackgroundPatent ductus arteriosus (PDA) is a common complication seen in preterm infants. Indomethacin is routinely used to treat PDA. Evidence suggests that the response of indomethacin is highly heritable. This study investigated the association between single-nucleotide polymorphisms (SNPs) in CYP2C9 and the closure of PDA in response to indomethacin.MethodsSix SNPs in CYP2C9 were analyzed for association with indomethacin response. A case-control analysis was performed among neonates who responded to indomethacin (responders) and among those who required surgical ligation (non-responders). Independent transmission disequilibrium tests were performed among parent-child trios of responders and non-responders.ResultsThe G allele of rs2153628 was associated with increased odds of response to indomethacin in the case-control analysis (odds ratios (OR): 1.918, 95% confidence interval (CI): 1.056, 3.483). Among indomethacin responders, the G allele of rs2153628 and the T allele of rs1799853 were overtransmitted from the parents to their child (OR: 2.667, 95% CI: 1.374, 5.177 and OR: 2.375, 95% CI: 1.040, 5.425, respectively), consistent with the case-control analysis.ConclusionWe identified an association between two SNPs in CYP2C9, rs2153628 and rs1799853, and indomethacin response for the treatment of PDA. These findings suggest that response to indomethacin in the closure of PDA may be influenced by polymorphisms associated with altered indomethacin metabolism.

Mechanisms of peroxisome proliferator activated receptor γ regulation by non-steroidal anti-inflammatory drugs

Non-steroidal anti-inflammatory drugs (NSAIDs) display anti-inflammatory, antipyretic and analgesic properties by inhibiting cyclooxygenases and blocking prostaglandin production. Previous studies, however, suggested that some NSAIDs also modulate peroxisome proliferator activated receptors (PPARs), raising the possibility that such off target effects contribute to the spectrum of clinically relevant NSAID actions. In this study, we set out to understand how peroxisome proliferator activated receptor-γ (PPARγ/PPARG) interacts with NSAIDs using X-ray crystallography and to relate ligand binding modes to effects on receptor activity. We find that several NSAIDs (sulindac sulfide, diclofenac, indomethacin and ibuprofen) bind PPARγ and modulate PPARγ activity at pharmacologically relevant concentrations. Diclofenac acts as a partial agonist and binds to the PPARγ ligand binding pocket (LBP) in typical partial agonist mode, near the β-sheets and helix 3. By contrast, two copies of indomethacin and sulindac sulfide bind the LBP and, in aggregate, these ligands engage in LBP contacts that resemble agonists. Accordingly, both compounds, and ibuprofen, act as strong partial agonists. Assessment of NSAID activities in PPARγ-dependent 3T3-L1 cells reveals that NSAIDs display adipogenic activities and exclusively regulate PPARγ-dependent target genes in a manner that is consistent with their observed binding modes. Further, PPARγ knockdown eliminates indomethacin activities at selected endogenous genes, confirming receptor-dependence of observed effects. We propose that it is important to consider how individual NSAIDs interact with PPARγ to understand their activities, and that it will be interesting to determine whether high dose NSAID therapies result in PPAR activation.

Clinical pharmacology of indomethacin in preterm infants: implications in patent ductus arteriosus closure

Indomethacin is a non-steroidal anti-inflammatory drug that is a potent inhibitor of prostaglandin E(2) synthesis. After birth, the ductus arteriosus closes spontaneously within 2-4 days in term infants. The major factor closing the ductus arteriosus is the tension of oxygen, which increases significantly after birth. Prostaglandin E(2) has the opposite effect to that of oxygen; it relaxes smooth muscle and tends to inhibit the closure of the ductus arteriosus. In preterm infants with respiratory distress syndrome, the ductus arteriosus fails to close (patent ductus arteriosus [PDA]) because the concentration of prostaglandin E2 is relatively high. PDA occurs in more than 70 % of neonates weighing less than 1,500 g at birth. The aim of this article was to review the published data on the clinical pharmacology of indomethacin in preterm infants in order to provide a critical analysis of the literature and a useful tool for physicians. The bibliographic search was performed electronically using the PubMed and EMBASE databases as search engines and February 2012 was the cutoff point. A remarkable interindividual variability was observed for the half-life (t(½)), clearance (CL), and volume of distribution (V(d)) of indomethacin. Prophylactic indomethacin consists of a continuous infusion of low levels of indomethacin and may be useful in preterm infants. Extremely preterm infants are less likely to respond to indomethacin. Infants with a postnatal age of 2 months do not respond to treatment with indomethacin. Indomethacin has several adverse effects, the most common of which is renal failure. An increase in serum creatinine of ≥0.5 % mg/dL after indomethacin was observed in about 10-15 % of the patients and creatinine returns to a normal level about 1 week after cessation of therapy. Indomethacin should be administered intravenously by syringe pump for at least 30 min to minimize adverse effects on cerebral, gastrointestinal, and renal blood flow velocities. A prolonged course of indomethacin appears to reduce the risk of severe intracranial hemorrhage and renal impairment in patients with PDA. In conclusion, indomethacin is a useful drug to treat PDA.

A pharmacokinetic standard for babies and adults

The pharmacokinetic behavior of medicines used in humans follows largely predictable patterns across the human age range from premature babies to elderly adults. Most of the differences associated with age are in fact due to differences in size. Additional considerations are required to describe the processes of maturation of clearance processes and postnatal changes in body composition. Application of standard approaches to reporting pharmacokinetic parameters is essential for comparative human pharmacokinetic studies from babies to adults. A standardized comparison of pharmacokinetic parameters obtained in children and adults is shown for 46 drugs. Appropriate size scaling shows that children (over 2 years old) are similar to adults. Maturation changes are generally completed within the first 2 years of postnatal life; consequently babies may be considered as immature children, whereas children are just small adults.

Population pharmacokinetic analysis during the first 2 years of life: an overview

Three decades after its introduction, pharmacokinetic population approaches have become a reference method for drug modelling, particularly in paediatrics. The main practical limitation in this specific population is the collected blood volume. Pharmacokinetic population approaches using sparse sampling may resolve this issue. The pharmacokinetics of many drugs have been studied during the last 25 years using such methods. This review summarizes all of the published studies concerning population pharmacokinetic approaches in paediatric subjects from neonate to 2 years old. A literature search was conducted using the PubMed database, from 1985 to December 2010, using the following terms: pharmacokinetic(s), population, paediatric/pediatric and neonate(s). Articles were excluded if they were not pertinent according to our criteria. References of all relevant articles were also evaluated. Ninety-eight studies were included in this review. The following information was extracted from the articles: drug name, therapeutic class, population size, age of patients, number of samples per patient, covariates used for clearance and volume of distribution estimates, software used for modelling and validation methods. An increasing rate of publications over the years was observed; 44 different drugs were studied using a pharmacokinetic population approach. Antibacterials were the most studied class of drugs, including a large number of studies devoted to vancomycin and gentamicin. It must be underlined that few studies have been performed on anticonvulsant drugs and anaesthetics used in clinical daily practice conditions.

Evidence-based use of indomethacin and ibuprofen in the neonatal intensive care unit

Indomethacin and ibuprofen are potent inhibitors of prostaglandin synthesis. Neonates have been exposed to these compounds for more than 3 decades. Indomethacin is commonly used to prevent intraventricular hemorrhage (IVH), and both drugs are prescribed for the treatment or prevention of patent ductus arteriosus (PDA). This review examines the basis for indomethacin and ibuprofen use in the neonatal intensive care population. Despite the call for restrained use of each drug, the most immature infants are likely to need pharmacologic approaches to reduce high-grade IVH, avoid the need for PDA ligation, and preserve the opportunity for an optimal outcome.

Pharmacologic, pharmacodynamic, and pharmacokinetic considerations with intravenous Ibuprofen lysine

Patent ductus arteriosus (PDA) is a common complication in preterm infants. An intravenous (IV) cyclooxygenase (COX) inhibitor is the pharmacotherapy of choice. Concerns over adverse effects associated with the traditional treatment, IV indomethacin, have led to the investigation of other COX inhibitors to assist closure of PDA. IV ibuprofen lysine is a COX inhibitor that demonstrates similar efficacy to indomethacin with few adverse effects. In addition, IV ibuprofen lysine does not cause reductions in cerebral, renal, and mesenteric blood flow that can be seen with indomethacin, and thus ibuprofen therapy is not associated with reduced renal function. Ibuprofen is primarily metabolized by cytochrome P450 (CYP) 2C9. The immaturity of neonatal biotransformation pathways has a pronounced effect on the pharmacokinetic parameters of ibuprofen, particularly because CYP2C9 enzyme activity is known to be very low at birth and to increase rapidly over the first several days of life. Ibuprofen is highly bound to albumin, raising concern that ibuprofen may displace bilirubin and subsequently increase free bilirubin concentrations. However, the ibuprofen concentrations achieved with approved dosing with IV ibuprofen lysine are lower than those expected to result in displacement of bilirubin and related adverse effects. Factors such as gestational age and CYP2C9 polymorphism may affect ibuprofen metabolism and therefore optimal dosing, but further clinical investigation is needed in these areas. Other areas for future investigation include prolonged dosing regimens, prophylactic administration, and alternate indications. At the approved dose, IV ibuprofen lysine is a safe, effective pharmacologic agent to promote closure of PDAs in preterm infants.

Pain control: non-steroidal anti-inflammatory agents

The non-steroidal anti-inflammatory drugs (NSAIDs) and acetaminophen (paracetamol) are the most common analgesic drugs used in neonates and infants despite limited pharmacodynamic data. Both drugs act through inhibition of cyclooxygenase enzymes. Neonatal acetaminophen clearance is reduced in premature neonates (0.7 L h(-1) x 70 kg(-1)) and increases to 5 L h(-1) x 70 kg(-1) at term (40% adult rates); adult rates are reached within the first year of life; NSAID clearance follows similar trends. Volume of distribution is increased in the neonatal period. Dosing of both drug groups is tempered by concerns about toxicity. Acetaminophen hepatotoxicity is less common in neonates than in older children and adults, possibly due to reduced oxidative enzyme activity (e.g. CYP 2E1). Data concerning NSAID adverse effects in the neonatal period are few. Renal function is reduced 20% after NSAID use for patent ductus arteriosus closure in premature neonates and there is no increased frequency of intraventricular haemorrhage. No significant difference in the change in cerebral blood volume, change in cerebral blood flow, or tissue oxygenation index was found between administration of ibuprofen or placebo in neonates. Future studies should define concentration-response relationships for these drugs that are age and pathology specific.

Recent pharmacological advances in paediatric analgesics

Growth and development are two linked processes that distinguish children from adults. The use of size as the primary covariate during pharmacokinetic (PK) analyses allows exploration of the effects of age. Allometric scaling models have assisted understanding of the developmental clearance changes in common analgesic drugs such as paracetamol, morphine, tramadol and local anaesthetics agents. Single nucleotide polymorphisms (pharmacogenomics [PG]) and their impact on hepatic drug metabolism for opioids, tramadol, non-steroidal anti-inflammatory drugs (NSAIDs) and drug receptor responses are increasingly reported. Altered chemical structure or formulations of common analgesics alter pharmacodynamic (PD) effects enhancing safety and efficacy for NSAIDs by stereoselectivity and the addition of nitric oxide, for intravenous paracetamol by formulation and structural difference from propacetamol and for local anaesthetics through stereoselectivity. This article focuses upon recent data for analgesics used in paediatric pain management including paracetamol, NSAIDs, morphine, tramadol, amide local anaesthetics and ketamine. It centres on PK and clinical studies in neonates, infants and children. PG studies are acknowledged as potentially allowing individual drug therapy tailoring through a decrease in between-patient population variability, although the impact of PG in the very young is less certain. There are few data describing age-related PD changes in children despite recognition that the number, affinity and type of receptors or the availability of natural ligands changes with age.

Recent developments in the pharmacological management of pain in children

PURPOSE OF REVIEW

This review explores progress in developmental pharmacokinetics, pharmacogenomics and formulations of analgesic agents, and discusses potential implications for pain therapy.

RECENT FINDINGS

Characterization of the developmental pharmacokinetics of morphine, tramadol, paracetamol and nonsteroidal anti-inflammatory drugs has improved dosing in children. Oral sugar solutions have replaced the brandy/sugar pacifier and are effective for single painful events in neonates. Intravenous paracetamol offers increased dosing accuracy, and avoids absorption and bioavailability variability. New nitric-oxide-releasing versions of paracetamol and nonsteroidal anti-inflammatory drugs offer safer alternatives to their parent drugs with enhanced potency. Ketamine has come under a cloud for its possible effects on the neonatal developing brain, but it is being used increasingly in children to supplement opioids for pain after major surgery. Hopes that morphine analgesia may improve neurological outcome in premature babies have not materialized. Reports concerning chronic pain are generally case series and controlled trials are rare and nearly nonexistent in children.

SUMMARY

Unlicensed drug use in the very young will increase as familiarity increases. Pharmacogenomic studies have the potential to tailor drug therapy to the individual and decrease between-patient variability. Unfortunately, the pharmacodynamic knowledge in children of analgesic agents remains neglected and is usually extrapolated from adult data.