Antimicrobial therapy in neonates, infants and children

Potential implications of DMET ontogeny on the disposition of commonly prescribed drugs in neonatal and pediatric intensive care units

Introduction: Pediatric patients, especially neonates and infants, are more susceptible to adverse drug events as compared to adults. In particular, immature small molecule drug metabolism and excretion can result in higher incidences of pediatric toxicity than adults if the pediatric dose is not adjusted.Area covered: We reviewed the top 29 small molecule drugs prescribed in neonatal and pediatric intensive care units and compiled the mechanisms of their metabolism and excretion. The ontogeny of Phase I and II drug metabolizing enzymes and transporters (DMETs), particularly relevant to these drugs, are summarized. The potential effects of DMET ontogeny on the metabolism and excretion of the top pediatric drugs were predicted. The current regulatory requirements and recommendations regarding safe and effective use of drugs in children are discussed. A few representative examples of the use of ontogeny-informed physiologically based pharmacokinetic (PBPK) models are highlighted.Expert opinion: Empirical prediction of pediatric drug dosing based on body weight or body-surface area from the adult parameters can be inaccurate because DMETs are not mature in children and the age-dependent maturation of these proteins is different. Ontogeny-informed-PBPK modeling provides a better alternative to predict the pharmacokinetics of drugs in children.

Prediction of Clearance, Volume of distribution, and Half-life of Drugs in Extremely Low to Low Birth Weight Neonates: An Allometric Approach

BACKGROUND AND OBJECTIVES

More than 20 million infants worldwide (15.5 % of all births) are born with low birth weight. Low birth weight is associated with poor growth in childhood and a higher incidence of adult diseases, such as type 2 diabetes, hypertension and cardiovascular disease. The objective of this study was to evaluate the predictive performance of allometric models to predict clearance, volume of distribution, and half-life in extremely low to low birth weight neonates (<1 to 2.5 kg body weight).

METHODS

Several allometric models were used to predict clearance (4 models), volume of distribution (2 models), and half-life (2 models) in extremely low to low birth weight neonates. From the literature, clearance, volume of distribution, and half-life values for 16 drugs for these neonates were obtained. The predictive performance of these allometric models was evaluated by comparing the predicted values of the aforementioned pharmacokinetic parameters with the observed pharmacokinetic parameters in an individual neonate. For the evaluation of the predictive performance of these allometric models, there were 16 drugs with 36 (n = 279), 34 (n = 261), and 31 (n = 197) weight groups for clearance, volume of distribution, and half-life, respectively.

RESULTS

The prediction error of ≤50 % for mean clearance, volume of distribution, and half-life values were 69, 79, and 58 %, respectively, by proposed allometric models. The prediction error of ≤50 % for mean clearance, volume of distribution, and half-life values by theoretical allometric exponents were 0 % (exponent = 0.75), 71 % (exponent = 1.0), and 0 % (exponent = 0.25), respectively. In this analysis, out of 16 drugs, there were three drugs (ibuprofen, zidovudine, and buprenorphine) which are metabolized by glucuronidation and one drug (furosemide) is renally secreted. The predicted clearances of these four drugs were substantially higher by the proposed allometric methods. It seems that drugs of these physiological characteristics may require different method(s) to improve the prediction of clearance in the neonates.

CONCLUSIONS

Overall, the proposed allometric methods can predict mean pharmacokinetic parameters of drugs in extremely low to low birth weight neonates with reasonable accuracy and are of practical value during neonatal drug development.

Drugs pharmacokinetics during veno-venous extracorporeal membrane oxygenation in pediatrics

Data evaluating pharmacokinetic/pharmacodynamic (PK/PD) aspect in the pediatric population are scarce especially regarding the pediatric intensive care unit. Dosing of frequently used drugs (sedatives, analgesics, antibiotics and cardiovascular drugs) are mainly based on non "pediatric intensive care unit (PICU)" patients, and sometimes are translated from adult patients. Among PICU patients, the most complex patients are the ones who are critically ill and are receiving mechanical circulatory/respiratory support for cardiac and/or respiratory failure. The use of extracorporeal membrane oxygenation is associated with major PK and PD changes, especially in neonates and children. The objective of this review is to assess the current literature for pediatric PK data in patients receiving extracorporeal membrane oxygenation (ECMO).

Paediatric pharmacokinetics: key considerations

A number of anatomical and physiological factors determine the pharmacokinetic profile of a drug. Differences in physiology in paediatric populations compared with adults can influence the concentration of drug within the plasma or tissue. Healthcare professionals need to be aware of anatomical and physiological changes that affect pharmacokinetic profiles of drugs to understand consequences of dose adjustments in infants and children. Pharmacokinetic clinical trials in children are complicated owing to the limitations on blood sample volumes and perception of pain in children resulting from blood sampling. There are alternative sampling techniques that can minimize the invasive nature of such trials. Population based models can also limit the sampling required from each individual by increasing the overall sample size to generate robust pharmacokinetic data. This review details key considerations in the design and development of paediatric pharmacokinetic clinical trials.

Factors and Mechanisms for Pharmacokinetic Differences between Pediatric Population and Adults

Many physiologic differences between children and adults may result in age-related changes in pharmacokinetics and pharmacodynamics. Factors such as gastric pH and emptying time, intestinal transit time, immaturity of secretion and activity of bile and pancreatic fluid among other factors determine the oral bioavailability of pediatric and adult populations. Anatomical, physiological and biochemical characteristics in children also affect the bioavailability of other routes of administration. Key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein binding and total body water. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I and phase II metabolic enzymes. Immaturity of glomerular filtration, renal tubular secretion and tubular reabsorption at birth and their maturation determine the different excretion of drugs in the pediatric population compared to adults.

Differences in absorption, distribution, metabolism and excretion of xenobiotics between the paediatric and adult populations

In children, the therapeutic benefits and potential risks associated with drug treatment may be different from those in adults and will depend on the exposure, receptor sensitivity and relationship between effect and exposure. In this paper, key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the paediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, secretion and activity of bile and pancreatic fluid, bacterial colonisation and transporters, such as P-glycoprotein (P-gp), are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the paediatric population and adults are organ size, membrane permeability, plasma protein concentration and characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and transporters such as P-gp, which is present not only in the gut, but also in liver, kidney, brain and other tissues. As far as drug metabolism is concerned, important differences have been found in the paediatric population compared with adults both for phase I enzymes (oxidative [e.g., cytochrome P450 (CYP)1A2, and CYP3A7 versus -3A4], reductive and hydrolytic enzymes) and phase II enzymes (e.g., N-methyltransferases and glucuronosyltransferases). Generally, the major enzyme differences observed in comparison with the adult age are in newborn infants, although for some enzymes (e.g., glucuronosyltransferases and other phase II enzymes) important differences still exist between infants and toddlers and adults. Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the paediatric population compared with adults are glomerular filtration and tubular secretion. The ranking of the key factors varies according to the chemical structure and physicochemical properties of the drug examined, as well as to the characteristics of its formulation. It would be important to generate additional information on the developmental aspects of renal P-gp and of other renal transporters, as has been done and is still being done with the different -isozymes involved in drug metabolism.

Clinical trials in children with Down syndrome: Issues from a cognitive research perspective

Clinical and translational research play a key role in the transition of basic research discoveries to effective therapies. In Down syndrome (DS), these research approaches are not well utilized or developed to test new therapies to improve cognitive and/or adaptive function in this population. This article reviews the history of clinical trial research in children with DS from a cognitive research perspective and discusses important issues relevant to the conduct of well designed clinical trials for this population. Specific issues addressed include: funding, study design, study medication, subject recruitment and retention, safety, and efficacy challenges. The Duke Down Syndrome Research Team's program of clinical research of cholinesterase inhibitors for individuals with DS serves as the model application for the identified research principles. It is hoped that this article will raise awareness of the unmet need for clinical research in the cognitive and adaptive function of individuals with DS, especially children with DS.

Vancomycin elimination in human infants with intrauterine growth retardation

BACKGROUND

Intrauterine growth retardation (IUGR) results in substantial decrease in nephron number and renal and hepatic organ mass in experimental animals and newborn infants. Because the liver and the kidneys are the major organs for drug biotransformation and elimination, any decrease in their size and function may lead to impaired metabolism and elimination of drugs in newborns with IUGR. Our objective was to test the hypothesis that IUGR results in prolonged renal elimination of vancomycin in newborns.

METHODS

Small for gestational age (SGA) infants (n = 20) were matched with appropriate for gestational age (AGA) infants (n = 123). Steady state peak and trough serum concentrations were used to calculate vancomycin clearance (Cl), volume of distribution (Vd) and half-life (t(1/2)) for each subject. Pharmacokinetic profiles were compared between groups.

RESULTS

Overall, Cl, Vd and t(1/2) of vancomycin were the same between groups. However, stratification showed decreased Cl in those SGA versus AGA newborns 3-4 weeks old and in those newborns with a postconceptional age of 27-29 weeks. There was no difference in Vd, normalized for weight, between SGA and AGA babies. The half-life of vancomycin was similar across most groups but was prolonged in SGA newborns aged 3-4 weeks.

CONCLUSIONS

Vancomycin Cl differs between SGA and AGA newborns. This difference is greatest early in life and normalizes between groups after the fourth week of life or after 29 weeks postconceptionally. Normalized Vd is similar between SGA and AGA newborns. The elimination of vancomycin is comparable between SGA and AGA infants, except before the fifth week of life, when SGA newborns may eliminate the drug more slowly. Specific vancomycin dose recommendations for SGA versus AGA neonates may therefore be justified during the first month of life.

Synthesis and characterization of novel 6-fluoro-4-piperidinyl-1,2-benzisoxazole amides and 6-fluoro-chroman-2-carboxamides: antimicrobial studies

Novel derivatives of 6-fluoro-4-piperidinyl-1,2-benzisoxazole amides 4(I-VI) were obtained by the condensation of different acid chlorides with 6-fluoro-3-piperidin-4yl-benzo[d]isoxazole. Also, 6-fluoro-chroman-2-carboxamides 6(I-III) were synthesized by using nebulic acid chloride with different amines in presence of triethylamine as acid scavenger and dichloroethane as solvent. The synthesized compounds were characterized by IR, 1H NMR, and CHN analysis. These molecules were evaluated for their efficacy as antimicrobials in vitro by disc diffusion and microdilution method against pathogenic strains such as Bacillus substilis, Escherichia coli, Pseudomonas fluorescens, Xanthomonas campestris pvs, X. oryzae, Aspergillus niger, A. flavus, Fusarium oxysporum, Trichoderma species, F. monaliforme, and Penicillum species. Compounds 4I, 4IV, 4V, 6I, 6II and 6III showed better inhibitory activity than compared to standard drugs. Among these compounds, 4IV and 6III showed potent inhibitory activity against all the strains and found to be nonstrain dependent. The title compounds represent a novel class of potent antimicrobial agents.

The Food and Drug Administration's deliberations on antidepressant use in pediatric patients

On February 2, 2004, the Food and Drug Administration organized a joint meeting of the Neuro-Psychopharmacologic Advisory Committee and Pediatric Subcommittee of the Anti-Infective Drugs Advisory Committee to examine the occurrence of suicidality in clinical trials that investigate the use of the newer antidepressant drugs in pediatric patients. Committee members reconvened on September 13-14, 2004, and concluded that there was a causal link between the newer antidepressants and pediatric suicidality. This article provides a summary of the Food and Drug Administration deliberations for the pediatric clinician. We also provide research, regulation, education, and practice implications for care for children and adolescents who may be eligible for treatment with these medications.

Role of biokinetics in risk assessment of drugs and chemicals in children

Whether children incur different risks from xenobiotics than adults will depend on the exposure, biokinetics, and dynamics of compound. In this paper, current knowledge on developmental physiology and possible effects on biokinetics are evaluated and the role of biokinetics in risk assessment both for drugs and chemicals is discussed. It is concluded that most dramatic age-related physiological changes that may affect biokinetics occur in the first 6-12 months of age. The difference in internal exposure between children and adults can generally be predicted from already known developmental physiological differences. However, for risk assessment it will also be necessary to determine whether internal exposure is within the drug's therapeutic window or if it will exceed the NOAEL of a chemical. Furthermore, the effects of internal exposure of potentially harmful compounds on developing organ systems is of utmost importance. However, knowledge on this aspect is very limited. Risk assessment in children could be improved by: (1) application of pediatric PBPK-models in order to gain insight into internal exposure in children, (2) studies in juvenile animals for studying effects on developing systems, and (3) extrapolation of knowledge on the relationship between internal exposure and dynamics for drugs to other chemicals.

Drug metabolism and disposition in children

Key factors undergoing maturational changes accounting for differences in drug metabolism and disposition in the pediatric population compared with adults are reviewed. Gastric and duodenal pH, gastric emptying time, intestinal transit time, bacterial colonization and probably P-glycoprotein are important factors for drug absorption, whereas key factors explaining differences in drug distribution between the pediatric population and adults are membrane permeability, plasma protein concentration and plasma protein characteristics, endogenous substances in plasma, total body and extracellular water, fat content, regional blood flow and probably P-glycoprotein, mainly that present in the gut, liver and brain. As far as drug metabolism is concerned, important differences have been found in the pediatric population compared with adults both for phase I enzymes [oxidative (e.g. cytochrome CYP3A7 vs. CYP3A4 and CYP1A2), reductive and hydrolytic enzymes] and phase II enzymes (e.g. N-methyltransferases and glucuronosyltransferases). Finally, key factors undergoing maturational changes accounting for differences in renal excretion in the pediatric population compared with adults are glomerular filtration and tubular secretion. It would be important to generate information on the developmental aspects of renal P-glycoprotein and of other renal transporters as done and still being done with the different isozymes involved in drug metabolism.

Prescription of antimicrobial drugs to hospitalized children

OBJECTIVE

To analyze with regard to age, gender, and diagnosis, the profile, frequency of prescribing, and cost of antimicrobial drugs (AMDs) in hospitalized children.

DESIGN

Retrospective study of medical records of children hospitalized during 1987 and 1988.

SETTING

First Pediatric Clinic, Children's Teaching Hospital, Bratislava, Czechoslovakia (now Slovakia).

PATIENTS

One thousand randomly selected hospitalized children.

MAIN OUTCOME MEASURES

Patterns of AMD prescribing. Consumption is expressed by the number of drugs and cost per child.

RESULTS

AMDs were prescribed to 69.9 percent of the patients (average 1.91 per patient). Ampicillin was the drug most frequently prescribed (20.0 percent), followed by oxacillin (12.8 percent). The mean length of stay was 15.9 days. An average of 3.61 drugs from other pharmacotherapeutic categories were prescribed per patient. Most children who received AMD treatment were in the 1-year group (patients between six months and 1.5 years of age [88.6 percent]).

CONCLUSIONS

This study provides an overview of the prescribing of AMDs and other drugs in hospitalized children in Bratislava.

Considerations in dosage selection for third generation cephalosporins

Pharmacokinetic parameters of third generation cephalosporins vary widely, requiring different dosage regimens and adjustment methods for each agent. Although their antibacterial spectrum favours their usage in infections caused by aerobic Gram-negative organisms, due to their limited post-antibiotic effect against these organisms, dosage regimens should ensure that free drug concentrations at the site of infection remain above the minimum inhibitory concentration for as much of the dosage interval as possible in patients with normal host defence mechanisms and for the entire dosage interval in immunocompromised patients. Altered protein binding encountered in various disease states can affect both microbiological and pharmacokinetic properties especially for drugs with high protein binding. Since the concentrations at the site of action are often different from those in serum, a higher or lower range of dosages needs to be selected depending on the target site. Decreased renal function affects the elimination of most third generation cephalosporins, whereas the presence of hepatic disease does not generally necessitate dosage adjustment. Because of the complex age-related physiological changes in paediatric and elderly patients, dosage should be adjusted on the basis of the reported pharmacokinetic data in these populations. The usual recommended dose may or may not be optimal in a given condition depending on the complex interactions between pharmacokinetic, microbiological and other host factors.