Pharmacokinetic and pharmacodynamic data collection in children and neonates. A quiet frontier

Paediatric Rheumatology Fails to Meet Current Benchmarks, a Call for Health Equity for Children Living with Juvenile Idiopathic Arthritis, Using Digital Health Technologies

PURPOSE OF REVIEW

This critical review begins by presenting the history of Juvenile Idiopathic Arthritis (JIA) management. To move the conversation forward in addressing the current shortcomings that exist in the clinical management of children living with JIA, we argue that to date, the advancement of successful treatments for JIA has been historically slow. Factors implicated in this situation include a lack of rigorous research, JIA being considered a rare disease, and JIA's idiopathic and complex pathophysiology.

RECENT FINDINGS

Despite the well-intended legislative changes to increase paediatric research, and the major advancements seen in molecular medicine over the last 30 years, globally, paediatric rheumatology services are still failing to meet the current benchmarks of best practice. Provoking questions on how the longstanding health care disparities of poor access and delayed treatment for children living with JIA can be improved, to improve healthcare outcomes. Globally, paediatric rheumatology services are failing to meet the current benchmarks of best practice. Raising awareness of the barriers hindering JIA management is the first step in reducing the current health inequalities experienced by children living with JIA. Action must be taken now, to train and well-equip the paediatric rheumatology interdisciplinary workforce. We propose, a resource-efficient way to improve the quality of care provided could be achieved by embedding digital health into clinical practice, to create an integrative care model between the children, general practice and the paediatric rheumatology team. To improve fragmented service delivery and the coordination of interdisciplinary care, across the healthcare system.

Survey of off-label prescribing in a university paediatric outpatient in Brazil

Ours is a cross-sectional, descriptive, retrospective study evaluating the extent of off-label prescribing for patients attending a university paediatric outpatient department in Goiás, Brazil. 391 patients were treated in the outpatient, and 668 medicines were prescribed. Of these, 70.4% followed the terms of the marketing authorization; 0.3% were unlicenced, and 11% were off-label. Dose was the main factor in off-label prescribing. Infants (0-2 years) received 37.8% of the off-label prescriptions. Vitamins and drugs for the treatment of respiratory diseases were the most prevalent culprits. Of the total prescriptions, 23 different drugs were defined as off-label. Salbutamol was the most prescribed (41.9%). Owing to practical and legal difficulties in carrying out clinical trials, medicines are inadequately studied in children; cooperation between industry, regulatory authorities, and healthcare professionals is required to improve treatment safety. Our results may help guide clinical researcher on off-label prescripting in future trials.

Providing Pharmaceutical Care to the Pediatric Patient

The purpose of this article is to provide the pharmacist with direction in providing pharmaceutical care to pediatric patients. A major component of the provision of pharmaceutical care is minimizing the risk for adverse drug effects such as medication errors. Dosage calculation errors are the most common type of medication error encountered in pediatric pharmacy practice. It is imperative that the pharmacist verify the dosages for all medication orders with appropriate dosage references. Establishing basic procedures for the processing of pediatric medication orders can reduce the risk for medication errors. One of the challenges in pediatric pharmacy practice is providing a drug product that is suitable for administration to infants and small children, because many of the commercial products are not. This may entail preparing a liquid formulation from a solid dosage form or instructing the caregiver on how to extract the contents out of a liquid-containing capsule. Providing the caregiver with suggestions on ways to improve the palatability of the medication can make a significant impact on patient compliance. The pediatric population is a very dynamic group of individuals who are constantly changing from the time of conception through adolescence. The physiological changes that occur with normal growth and development alter the pharmacodynamics and pharmacokinetics of therapeutic agents. The pharmaceutical care team must be versed in the unique aspects of these patients to best meet their drug therapy needs and achieve the desired therapeutic outcomes. As the expert in pharmacotherapy and pharmaceutics, the pharmacist is a key member of the pharmaceutical care team. Copyright © 1996 by W.B. Saunders Company

Comparative Effectiveness Research Through a Collaborative Electronic Reporting Consortium

The United States lacks a system to use routinely collected electronic health record (EHR) clinical data to conduct comparative effectiveness research (CER) on pediatric drug therapeutics and other child health topics. This Special Article describes the creation and details of a network of EHR networks devised to use clinical data in EHRs for conducting CER, led by the American Academy of Pediatrics Pediatric Research in Office Settings (PROS). To achieve this goal, PROS has linked data from its own EHR-based "ePROS" network with data from independent practices and health systems across the United States. Beginning with 4 of proof-of-concept retrospective CER studies on psychotropic and asthma medication use and side effects with a planned full-scale prospective CER study on treatment of pediatric hypertension, the Comparative Effectiveness Research Through Collaborative Electronic Reporting (CER(2)) collaborators are developing a platform to advance the methodology of pediatric pharmacoepidemiology. CER(2) will provide a resource for future CER studies in pediatric drug therapeutics and other child health topics. This article outlines the vision for and present composition of this network, governance, and challenges and opportunities for using the network to advance child health and health care. The goal of this network is to engage child health researchers from around the United States in participating in collaborative research using the CER(2) database.

Population pharmacokinetics of etomidate in neonates and infants with congenital heart disease

BACKGROUND

Etomidate is a rapid-onset, short-acting hypnotic medication administered for the induction of anesthesia. It is currently approved by the Food and Drug Administration for use in older children and adults. Pharmacokinetic data to help guide dosing in neonates and infants are lacking.

OBJECTIVE

The aim of this study was to determine the pharmacokinetics of etomidate in neonates and infants with congenital heart disease undergoing cardiac surgery.

METHODS

Four neonates and 16 infants, postnatal age 0.3-11.7 months, requiring open-heart surgery received 0.3 mg/kg of etomidate administered as a single intravenous dose prior to surgery. Blood sampling for plasma etomidate concentration occurred immediately following etomidate administration until the initiation of cardiopulmonary bypass. A population pharmacokinetic approach using nonlinear mixed-effects modeling was applied to characterize etomidate pharmacokinetics.

RESULTS

The pharmacokinetics of etomidate was described by a two-compartment model with first-order elimination. An allometric weight-based model was applied to scale results to a 70 kg adult. Covariates including age and cardiac physiology were not found significantly to impact etomidate pharmacokinetics. The study population was found to have a central and intercompartmental clearance of 0.624 l/min/70 kg and 0.44 l/min/70 kg, respectively; central and peripheral distribution volume of 9.47 l/70 kgand 22.8 l/70 kg, respectively. Inter-individual variability was 94-142% for all parameters and the residual variability was 29%.

CONCLUSIONS

The clearance of etomidate is lower in neonates and infants with congenital heart disease compared with published values for older children without congenital heart disease. In addition, etomidate pharmacokinetics is highly variable in this pediatric cardiac population.

Medication errors--new approaches to prevention

Medication errors in pediatric anesthesia represent an important risk to children. Concerted action to reduce harm from this cause is overdue. An understanding of the genesis of avoidable adverse drug events may facilitate the development of effective countermeasures to the events or their effects. Errors include those involving the automatic system of cognition and those involving the reflective system. Errors and violations are distinct, but violations often predispose to error. The system of medication administration is complex, and many aspects of it are conducive to error. Evidence-based practices to reduce the risk of medication error in general include those encompassed by the following recommendations: systematic countermeasures should be used to decrease the number of drug administration errors in anesthesia; the label on any drug ampoule or syringe should be read carefully before a drug is drawn up or injected; the legibility and contents of labels on ampoules and syringes should be optimized according to agreed standards; syringes should always be labeled; formal organization of drug drawers and workspaces should be used; labels should be checked with a second person or a device before a drug is drawn up or administered. Dosage errors are particularly common in pediatric patients. Causes that should be addressed include a lack of pediatric formulations and/or presentations of medication that necessitates dilution before administration or the use of intravenous formulations for oral administration in children, a frequent failure to obtain accurate weights for patients and a paucity of pharmacokinetic and pharmacodynamic data. Technological innovations, including the use of bar codes and various cognitive aids, may facilitate compliance with these recommendations. Improved medication safety requires a system-wide strategy standardized at least to the level of the institution; it is the responsibility of institutional leadership to introduce such strategies and of individual practitioners to engage in them.

Limited capacity in US pediatric drug trials: qualitative analysis of expert interviews

BACKGROUND

The recently renewed Best Pharmaceuticals for Children and Pediatric Research Equity Acts (BPCA/PREA) have continued industry incentives and opportunities for pediatric drug trials (PDTs). However, there is no current assessment of the capacity to perform PDTs.

OBJECTIVE

The aim of this study was to deepen understanding of the capacity for US PDTs by assessing PDT infrastructure, present barriers to PDTs, and potential approaches and solutions to identified issues.

DESIGN METHODS

Pediatric clinical research experts participated in semi-structured interviews on current US pediatric research capacity (February-July 2007). An initial informant list was developed using purposive sampling, and supplemented and refined to generate a group of respondents to explore emerging themes. Each phone interview included a physician researcher and two health researchers who took notes and recorded the calls. Health researchers produced detailed summaries, which were verified by the physician researcher and informants. We then undertook qualitative analysis of the summaries, employing multiple coding, with the two health researchers and the physician researcher independently coding each summary for themes and subthemes. Coding variations were resolved by physician researcher/health researcher discussion and consensus achieved on themes and subthemes.

RESULTS

The 33 informants' primary or secondary roles included academia (n = 21), federal official (5), industry medical officer (8), pediatric research network leader (10), pediatric specialist leader (8), pediatric clinical pharmacologist (5), and practitioner/research site director (9). While most experts noted an increase in PDTs since the initial passage of BPCA/PREA, a dominant theme of insufficient US PDT capacity emerged. Subthemes included (i) lack of systems for finding, incentivizing, and/or maintaining trial sites; (ii) complexity/demands of conducting PDTs in clinical settings; (iii) inadequate numbers of qualified pediatric pharmacologists and clinician investigators trained in FDA Good Clinical Practice; and (iv) poor PDT protocol design resulting in operational and enrollment difficulties in the pediatric population. Suggested potential solutions for insufficient PDT capacity included (i) consensus-building among stakeholders to create PDT systems; (ii) initiatives to train more pediatric pharmacologists and educate clinicians in Good Clinical Practice; (iii) advocacy for PDT protocols designed by individuals sensitive to pediatric issues; and (iv) physician and public education on the importance of PDTs.

CONCLUSIONS

Insufficient US PDT capacity may hinder the development of new drugs for children and limit studies on the safety and efficacy of drugs presently used to treat pediatric conditions. Further public policy initiatives may be needed to achieve the full promise of BPCA/PREA.

Dosing information in a standard drug reference: are pediatrics still therapeutically neglected?

BACKGROUND

In many countries, the most readily accessible drug information resources, such as the Monthly Index of Medical Specialties (MIMS), lack information concerning use in children. We reviewed the product information (PI) of medications in the most widely used drug information reference in Malaysia in an effort to determine the extent and the nature of available information related to pediatric dosing.

METHODS

The products listed in the 2007 Malaysian MIMS Annual were reviewed for PI on pediatric use as per inclusion and exclusion criteria. The dosing information for each PI was extracted according to age groups. Product information that claimed suitability for use in pediatrics was further evaluated for information on pediatric dosage formulations.

RESULTS

A total of 421 PI items from seven categories of therapeutic classes were reviewed. Of these, 69% gave inadequate pediatric dosing information. The proportions, for each age group of PI items that gave adequate pediatric dosing information were: neonates (13.1%), infants (23.3%), and children (32.2%). Therapeutic classes of drugs differed significantly in terms of dosing information adequacy for all pediatric age groups (P < 0.05). Most PI reviewed under all legal categories provided inadequate pediatric dosing information, but suitable pediatric formulations were commonly (70.1-85.5%) available where the dosing information existed. Overall, category B (prescription only) products did not differ significantly from category C (pharmacy only medicine) products in terms of pediatric dosing information adequacy, except for children.

CONCLUSION

This study has managed to contribute substantial additional information regarding the extent of pediatric dosing information and dosage formulations available in the MIMS Annual, stressing that the majority of PI for the products reviewed did not provide adequate dosing information for pediatric patients, subjecting this population to a therapeutically disadvantaged status.

Safety and transparency of pediatric drug trials

OBJECTIVES

To quantify the frequency and type of new safety information arising from studies performed under the auspices of the Pediatric Exclusivity Program, to describe the dissemination of these findings in the peer-reviewed literature and compare this with the US Food and Drug Administration (FDA) review, and to describe their effect on pediatric labeling.

DESIGN

Cohort study of the 365 trials performed for 153 drugs.

SETTING

The Pediatric Exclusivity incentive from December 1997 through September 2007.

PARTICIPANTS

Food and Drug Administration publicly available records and peer-reviewed literature retrievable by MEDLINE search. Main Exposures New safety findings obtained from the trials completed for exclusivity.

OUTCOME MEASURES

Concordance of the information highlighted in the peer-reviewed article abstracts with the information in the FDA labeling and drug reviews.

RESULTS

There were 137 labeling changes; we evaluated 129 of these (the 8 selective serotonin reuptake inhibitors were excluded from review). Thirty-three products (26%) had pediatric safety information added to the labeling. Of these, 12 products had neuropsychiatric safety findings and 21 had other important safety findings. Only 16 of 33 of these trials (48%) were reported in the peer-reviewed literature; however, 7 of 16 focused on findings substantively different from those highlighted in the FDA reviews and labeling changes.

CONCLUSIONS

Medication adverse events in children often differ from those in adults, particularly those that are neuropsychiatric in nature. Labeling changes for pediatric use demonstrate that pediatric drug studies provide valuable and unique safety data that can guide the use of these drugs in children. Unfortunately, most of these articles are not published, and almost half of the published articles focus their attention away from the crucial safety data.

Safety monitoring of drugs receiving pediatric marketing exclusivity

OBJECTIVES

The Food and Drug Administration Modernization Act provided for an additional 6-month period of marketing exclusivity to companies that perform pediatric drug trials in response to a Food and Drug Administration-issued written request. Because many safety concerns cannot be detected until after the introduction of a product to a larger and more diverse market, the Best Pharmaceuticals for Children Act required the Food and Drug Administration to report to the Pediatric Advisory Committee on adverse events occurring during the 1-year period after granting pediatric exclusivity. We sought to describe the Pediatric Advisory Committee's recommendations made in response to safety reviews informed by data from the Food and Drug Administration Adverse Event Reporting System in 67 drugs granted exclusivity.

PATIENTS AND METHODS

Pediatric Advisory Committee meetings and data presented by the Food and Drug Administration for all drugs were reviewed from June 2003 through April 2007. We divided the drugs into 2 groups: those that were returned to routine adverse event monitoring and those that had specific Pediatric Advisory Committee recommendations.

RESULTS

Forty-four (65.7%) drugs were returned to routine monitoring for adverse events. The Pediatric Advisory Committee, sometimes working with other advisory committees, recommended label changes for 12 (17.9%) drugs, continued monitoring for 10 (14.9%), production of MedGuides for 9 (13.4%), and an update on label changes resulting from discussions with the sponsor for 1 (1.5%) drug. Some drugs had >1 action. Several of the adverse events revealed during this process were rare and life-threatening.

CONCLUSIONS

Safety monitoring during the early postmarketing period is crucial to detect rare, serious, or pediatric-specific adverse events. Fortunately, the majority of drugs given exclusivity had no adverse events of a frequency or severity that prevented a return to routine adverse event monitoring.

Off-label and unlicensed drug utilization in hospitalized children in Fortaleza, Brazil

OBJECTIVES

To investigate the use of drugs, the extent and pattern of unlicensed and off-label use, and the potential relationship between off-label drug use and adverse drug reactions in northeastern Brazil.

METHODS

A follow-up study of drug utilization in a general ward of a pediatric reference hospital, involving patients hospitalized for more than 24 h. Prescriptions and medical records were reviewed daily from August to December 2001. Drug licensing status of all prescriptions given to these patients was determined.

RESULTS

A total of 272 patients were admitted during the study, 265 (97.4%) of whom received one or more drugs. The median number of drugs/patient was 6 (1-18), and the most frequent diagnosis was pneumonia (29.4% of patients). The therapeutic class most prescribed was anti-infectives for systemic use (68.8% of all children). In all, 82.6% of children received at least one unlicensed or off-label drug, and 17% received both an unlicensed and an off-label drug. Dose/frequency was the most common form of off-label drug use. Off-label drug use was significantly associated with adverse drug reactions (relative risk 2.44; 95% CI 2.12, 2.89).

CONCLUSIONS

Although off-label drug use is a complex issue and is not synonymous with inappropriate drug use, a high rate of unlicensed/off-label drug use was found and was also associated with an increased risk of adverse drug reactions. More efforts are needed to increase rational drug use in children.

Pharmacokinetics and pharmacodynamics of gatifloxacin in children with recurrent otitis media: application of sparse sampling in clinical development

Gatifloxacin is a 4th-generation fluoroquinolone previously under investigation for the treatment of otitis media in infants and children. These analyses were designed to evaluate the extent of drug exposure relative to adult populations and to examine the relationship between drug exposure and response to therapy in children with recurrent otitis media or early treatment failures of acute otitis media. The patient population included 187 patients from an open-label, multicenter, noncomparative study using gatifloxacin 10 mg/kg once daily. Gatifloxacin exposure was estimated using a single steady-state blood sample in conjunction with a pharmacostatistical model developed using a separate pediatric data set. Gatifloxacin exposure was equivalent to that in adults given 400 mg daily. Of the 41 patients who had Streptococcus pneumoniae from middle ear culture, there were only 3 bacteriologic failures; there was no relationship between plasma fu AUC(0-24):MIC ratio and outcome. In conclusion, population pharmacokinetic/pharmacodynamic methods allowed estimation of drug exposure using one sample per patient.

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.

Reported medication use in the neonatal intensive care unit: data from a large national data set

OBJECTIVES

The objectives were (1) to identify the drugs reported most commonly during NICU care, (2) to examine how different methods of documenting drug use could influence prioritization of drugs for future research aimed at evaluating safety and efficacy, (3) to describe the demographic differences in the population samples for some specific medications, (4) to identify which reported medications are used for patient populations with >20% mortality rates, and (5) to examine how reports of drug use change over time.

METHODS

A retrospective review of a large national data set was performed.

RESULTS

The 10 medications reported most commonly for the NICU were ampicillin, gentamicin, ferrous sulfate, multivitamins, cefotaxime, caffeine citrate, furosemide, vancomycin, surfactant, and metoclopramide. Medications used for patient populations with >20% mortality rates included amphotericin, clonazepam, dobutamine, epinephrine, ethacrynic acid, insulin, lidocaine, metolazone, milrinone, inhaled nitric oxide, nitroglycerin, octreotide, pancuronium, phenytoin, sodium nitroprusside, sodium polystyrene sulfonate (Kayexalate), tris-hydroxymethylaminomethane acetate buffer, and tolazoline. Several of these drugs (eg, amphotericin B and bumetanide) were used primarily for extremely premature neonates, and this usage might explain the high mortality rates for the population of neonates treated with these medications. Other medications (clonazepam, milrinone, inhaled nitric oxide, and phenytoin) were used primarily for near-term and term infants. The explanation for the high mortality rates for these neonates is less clear and may be related primarily to the severity of illness for which the medications are used. Utilization rates for several different medications (eg, cisapride, metoclopramide, and dexamethasone) changed by >50% during the past 5 years.

CONCLUSIONS

Data reported here are the first from a large national data set on the use of different medications for neonates admitted for intensive care and should be helpful in establishing priority agendas for future drug studies in this population.

Population pharmacokinetics of pyrimethamine and sulfadoxine in children treated for congenital toxoplasmosis

The population pharmacokinetics of pyrimethamine (PYR) and sulfadoxine (SDX) for a group of 32 children with congenital toxoplasmosis was investigated by nonparametric modeling analysis. A one-compartment model was used as the structural model, and individual pharmacokinetic parameters were estimated by Bayesian modeling. PYR (1.25 mg/kg of body weight) and SDX (25 mg/kg) were administered orally every 10 days for 1 year, with adjustment of the dose to body weight every 3 months. Drug concentrations were measured by high-performance liquid chromatography. A total of 101 measurements in serum were available for both drugs. Mean absorption rate constants, volumes of distribution, elimination rate constants, and half-lives were 0.915 h(-1), 4.379 liters/kg, 0.00839 h(-1), and 5.5 days for PYR and 1.659 h(-1), 0.392 liters/kg, 0.00526 h(-1), and 6.6 days for SDX, respectively. Wide interindividual variability was observed. The estimated minimum and maximum concentrations of PYR in serum differed 8- and 25-fold among patients, respectively, and those of SDX differed 4- and 5-fold, respectively. Increases in the concentration of PYR were observed for eight children, and increases in the SDX concentration were observed for seven children. Serum PYR-SDX concentrations are unpredictable even when the dose is standardized for body weight. The concentrations of the PYR-SDX combination that are most efficacious for children have not yet been established. A model such as ours, associated with long-term follow-up, is needed to study the correlation between exposure to these two drugs and clinical outcome in children.

Transdermal reverse iontophoresis of valproate: a noninvasive method for therapeutic drug monitoring

PURPOSE

The objectives of this work were (a) to explore the potential of transdermal reverse iontophoresis for therapeutic drug monitoring and (b) to develop an "internal standard" calibration procedure so as to render the technique completely noninvasive.

METHODS

A series of in vitro iontophoresis experiments was performed in which the subdermal concentration of sodium valproate was varied from 21 microM to 1 mM. Glutamic acid was also introduced into the subdermal donor at a fixed concentration to act as an "internal standard" for the calibration method.

RESULTS

Both valproate and glutamate anions were recovered, as expected, at the anodal receptor chamber. The iontophoretic extraction flux of valproate was linearly correlated with the subdermal concentration. Glutamate flux was constant. It follows that the ratio of extracted fluxes (valproate/glutamate) was directly dependent upon (a) the subdermal valproate concentration and (b) the subdermal concentration ratio (valproate/glutamate), offering a means, thereby, to a completely noninvasive methodology.

CONCLUSIONS

This work demonstrates the potential of reverse iontophoresis for noninvasive therapeutic monitoring. The simultaneous quantification of the analyte of interest and of an "internal standard" renders the withdrawal of a blood sample unnecessary.

Population pharmacokinetics of arbekacin, vancomycin, and panipenem in neonates

Immature renal function in neonates requires antibiotic dosage adjustment. Population pharmacokinetic studies were performed to determine the optimal dosage regimens for three types of antibiotics: an aminoglycoside, arbekacin; a glycopeptide, vancomycin; and a carbapenem, panipenem. Eighty-three neonates received arbekacin (n = 41), vancomycin (n = 19), or panipenem (n = 23). The postconceptional ages (PCAs) were 24.1 to 48.4 weeks, and the body weights (BWs) ranged from 458 to 5,200 g. A one-compartment open model with first-order elimination was applied and evaluated with a nonlinear mixed-effect model for population pharmacokinetic analysis. In the fitting process, the fixed effects significantly related to clearance (CL) were PCA, postnatal age, gestational age, BW, and serum creatinine level; and the fixed effect significantly related to the volume of distribution (V) was BW. The final formulas for the population pharmacokinetic parameters are as follows: CL(arbekacin) = 0.0238 x BW/serum creatinine level for PCAs of <33 weeks and CL(arbekacin) = 0.0367 x BW/serum creatinine level for PCAs of > or = 33 weeks, V(arbekacin) = 0.54 liters/kg, CL(vancomycin) = 0.0250 x BW/serum creatinine level for PCAs of <34 weeks and CL(vancomycin) = 0.0323 x BW/serum creatinine level for PCAs of > or = 34 weeks, V(vancomycin) = 0.66 liters/kg, CL(panipenem) = 0.0832 for PCAs of <33 weeks and CL(panipenem) = 0.179 x BW for PCAs of > or = 33 weeks, and V(panipenem) = 0.53 liters/kg. When the CL of each drug was evaluated by the nonlinear mixed-effect model, we found that the mean CL for subjects with PCAs of <33 to 34 weeks was significantly smaller than those with PCAs of > or = 33 to 34 weeks, and CL showed an exponential increase with PCA. Many antibiotics are excreted by glomerular filtration, and maturation of glomerular filtration is the most important factor for estimation of antibiotic clearance. Clinicians should consider PCA, serum creatinine level, BW, and chemical features when determining the initial antibiotic dosing regimen for neonates.

Dosing information for paediatric patients: are they really "therapeutic orphans"?

OBJECTIVES

To review the approved product information (PI) of prescription medicines to determine the extent and nature of information available on paediatric dosing and the availability of paediatric dosage formulations in Australia.

METHODS

The PIs for all prescription medicines listed in the Australian Monthly Index of Medical Specialties (MIMS) were reviewed. Dosing information for each PI was categorised according to age groupings. PIs claiming suitability for use in paediatric patients were reviewed for information on the availability of paediatric dosage forms.

MAIN OUTCOME MEASURES

Proportion of PIs providing paediatric dosing information; availability of dosage forms suitable for children.

RESULTS

A total of 1497 PIs were reviewed. The proportions, for each age group, of PIs with inadequate paediatric dosing information were: < 1 month (80.5%), 1-3 months (79.1%), 3 months-2 years (77.5%), 2-6 years (73.2%), and 6-12 years (71.6%). The proportions, for each age group, of PIs that gave specific paediatric dosing information but did not provide a paediatric dosage form were: < 1 month (26.5%), 1-3 months (25.1%), 3 months-2 years (23.3%), 2-6 years (21.9%), and 6-12 years (24.0%).

CONCLUSIONS

The PIs for many prescription products listed in MIMS do not adequately detail paediatric doses. Many medicines for which specific paediatric dosing information is given are not available in dosage forms appropriate for children.

Pharmacokinetic considerations in the treatment of childhood epilepsy

Organogenesis throughout childhood affects almost every aspect of pediatric pharmacotherapy. The antiepileptic drugs (AEDs) are particularly impacted since most elimination rates are diminished for the first 6 months of infancy, but quickly attain and supersede adult values. When children enter a hypermetabolic stage, large doses of AEDs may be necessary to maintain effective serum concentrations. Medication noncompliance is frequently confused as hypermetabolism, since both present with low serum drug concentrations. Amazingly, noncompliance among children with chronic illness approaches a similar incidence to that reported in the adult population. It is obviously important to include this in the differential diagnosis of the etiology of subtherapeutic serum AED concentrations. Maturational differences also affect gastrointestinal drug absorption. Intestinal transit time and absorptive surface area are both diminished in young children. Drug delivery systems suitable in adults may not deliver the total dosage in children. Differences in the composition of body compartments and protein binding can alter the volume of drug distribution and, consequently, serum concentrations. In addition to pathophysiologic changes, there is evidence to suggest differences between a mature and immature brain. These differences include quantitative and qualitative responses to neurotransmitters. Hence, it is understandable why seizure semiology is different in children compared with adults. This constellation of factors contributes to the challenges of caring for children with epilepsy.

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.

Developmental and pediatric pharmacogenomics

Children, as well as adults, should benefit from the discoveries of the genomic era. Many diseases with complex etiologies originate during childhood (e.g., asthma, autism, attention deficit/hyperactivity disorder, epilepsy and juvenile rheumatoid arthritis) and persist into adulthood. Attempts to better understand the genetic basis of age-specific disease processes requires an appreciation that the period of human development encompasses the prenatal period through adolescence, and is a rapidly changing, dynamic process. As a result, pharmacologic modulation of developing gene networks may have unintended and unanticipated consequences that do not become apparent or relevant until later in life. Thus, there is considerable potential for large-scale pharmacogenomic technologies to impact the development and utilization of new therapeutic strategies in children.

Determinants for drug prescribing to children below the minimum licensed age

OBJECTIVES

In the light of the undesired effects that unlicensed and off-label drug use might have, it is necessary to study the determinants affecting the prescribing of such drugs. Prescription of drugs to children younger than the minimum licensed age may carry the highest risk of adverse reactions. To obtain insight into the factors that affect prescription of drugs to children below the minimum licensed age, we conducted a population-based case-control study.

METHODS

The case-control study was nested in a cohort of 13,426 children aged 0-16 years, who were registered in the Integrated Primary Care Information (IPCI) project, a longitudinal observational general practitioners' database in the Netherlands. "Cases" were children who received a drug prescription for which they were below the minimum licensed age. To each case we matched up to four controls based on GP practice and patient age. As potential risk factors we evaluated the use of health care resources, and acute and chronic morbidity.

RESULTS

We identified 447 cases who were matched to 1355 controls. The cases consulted their GPs significantly more often during the preceding half year, had more drug prescriptions, and had more specialist referrals than the controls. Respiratory diseases were the most important determinants for the prescription of drugs to children below the minimum licensed age. In adolescents, migraine and other headaches were the most important reasons.

CONCLUSIONS

This study showed that children suffering from respiratory disease or migraine have the highest risk of receiving a drug prescription for which the patient is below the minimum licensed age. Regulatory authorities and the pharmaceutical industry should be stimulated to improve the evaluation of drug efficacy and safety in children.

Ontogeny of hepatic and renal systemic clearance pathways in infants: part I

Dramatic developmental changes in the physiological and biochemical processes that govern drug pharmacokinetics and pharmacodynamics occur during the first year of life. These changes may have significant consequences for the way infants respond to and deal with drugs. The ontogenesis of systemic clearance mechanisms is probably the most critical determinant of a pharmacological response in the developing infant. In recent years, advances in molecular techniques and an increased availability of fetal and infant tissues have afforded enhanced insight into the ontogeny of clearance mechanisms. Information from these studies is reviewed to highlight the dynamic and complex nature of developmental changes in clearance mechanisms in infants during the first year of life. Hepatic and renal elimination mechanisms constitute the two principal clearance pathways of the developing infant. Drug metabolising enzyme activity is primarily responsible for the hepatic clearance of many drugs. In general, when compared with adult activity levels normalised to amount of hepatic microsomal protein, hepatic cytochrome P450-mediated metabolism and the phase II reactions of glucuronidation, glutathione conjugation and acetylation are deficient in the neonate, but sulfate conjugation is an efficient pathway at birth. Parturition triggers the dramatic development of drug metabolising enzymes, and each enzyme demonstrates an independent rate and pattern of maturation. Marked interindividual variability is associated with their developmental expression, making the ontogenesis of hepatic metabolism a highly variable process. By the first year of life, most enzymes have matured to adult activity levels. When compared with adult values, renal clearance mechanisms are compromised at birth. Dramatic increases in renal function occur in the ensuing postpartum period, and by 6 months of age glomerular filtration rate normalised to bodyweight has approached adult values. Maturation of renal tubular functions exhibits a more protracted time course of development, resulting in a glomerulotubular imbalance. This imbalance exists until adult renal tubule function values are approached by 1 year of age. The ontogeny of hepatic biliary and renal tubular transport processes and their impact on the elimination of drugs remain largely unknown. The summary of the current understanding of the ontogeny of individual pathways of hepatic and renal elimination presented in this review should serve as a basis for the continued accruement of age-specific information concerning the ontogeny of clearance mechanisms in infants. Such information can only help to improve the pharmacotherapeutic management of paediatric patients.

Potential benefit of Bayesian forecasting for therapeutic drug monitoring in neonates

Therapeutic drug monitoring in neonate has been hampered by invasiveness of blood samplings raising ethical problems. A methodologic approach has been developped in adults and in children that is still unsufficiently developped in neonates, the Bayesian forecasting of drug plasma concentration. This method is particularly attractive in neonates using a few blood samples from an individual patient and more informations from a prior patient sample representative of the population the individual patient belongs to. The present article aims at reviewing the different procedures and methods to minimize invasiveness during therapeutic drug monitoring in neonate and at reviewing the methods for improving the quality of different dose adjustments using a Bayesian approach.

A survey of the use of off-label and unlicensed drugs in a Dutch children's hospital

BACKGROUND

The treatment of pediatric patients with drugs in hospitals is being impeded by a shortage in the availability of licensed drugs in an appropriate formulation. We have studied the extent of use of drugs that are not licensed for use in children (unlicensed) and drugs that are used outside the terms of the product license (off-label). We conducted this study in a Dutch academic children's hospital.

METHODS

In a prospective study of 5 weeks' duration, we reviewed drug prescriptions in a pediatric ward and 3 intensive care units. We classified the prescribed drugs in 3 main categories-licensed, unlicensed, and off-label-and determined the nature of their unlicensed and off-label use.

RESULTS

Two thousand one hundred thirty-nine courses of drugs were administered to 237 patients in 442 patient-days. Of 2139 prescriptions, 725 (34%) were licensed, 1024 (48%) were unlicensed, and 390 (18%) were off-label. In 392 (90%) of 435 patient-days, children received 1 or more courses of an unlicensed or off-label drug prescription in hospital.

CONCLUSION

With regard to the availability of drugs of proven quality and adequate license for pediatric patients in hospital, dramatic shortcomings exist. As a result, drug legislation originally designed to protect patients and prescribing physicians against unsafe drug use and unjustified claims has turned into an insurmountable threshold to make proper drugs available for a vulnerable minority of patients.

Population kinetics of tobramycin in neonates

The population kinetics of tobramycin were studied in 140 neonates (100/40 patients for the index/validation groups, respectively) of 30 to 42 weeks' gestational age and 0.8 to 4.25 kg current body weight in their first 2 weeks of life, undergoing routine therapeutic drug monitoring of their tobramycin serum levels. The 365 tobramycin concentration measurements obtained were analyzed by use of NONMEM according to a one-compartment open model with zero-order absorption and first-order elimination. The effect of a variety of demographic, developmental, and clinical factors (gender, height, birth weight, current weight, gestational age, postnatal age, postconceptional age, and serum creatinine concentration) on clearance and volume of distribution was investigated. Forward selection and backward elimination regression identified significant covariates. The final pharmacostatistical model with influential covariates was as follows (full population): clearance (L/h) = 0.0508 x current weight (kg), multiplied by 0.843 if birth weight was 2.5 kg or less (low-birthweight infants), and volume of distribution (L) = 0.533 x current weight (kg). Using the proportional error model for the random-effects parameters, interindividual variability for clearance and for volume of distribution was determined to be 25.8% and 21.9%, respectively, and the residual variability was 19.2%. In this study, the use of the NONMEM gave significant and consistent information on the pharmacokinetics and the determinants of the pharmacokinetic variability of tobramycin in neonates when compared with available bibliographic information. Moreover, the final population pharmacokinetic model may be used to design a priori recommendations for tobramycin and to improve the dosing readjustments through Bayesian estimation.

Clinical pharmacology research in the pediatric patient: the challenge continues

For most of the 20th century, most drugs labeled by the United States Food and Drug Administration (USFDA) have not been adequately studied in the pediatric population. This lack of data has necessitated the continued dependence of practitioners on sub-optimal prescribing data placing pediatric patients at great risk of serious therapeutic misadventures. Recently, the USFDA has enacted and begun to enforce the Final Rule of 1997 which became effective on 1 April 1999. This rule is the culmination of the persistent efforts of numerous professional organizations, clinicians, academicians, the USFDA and others, to ensure the ready availability of appropriate data for medications intended for or that will be used in children. Unlike the 1994 Rule which voluntarily required pharmaceutical manufacturers to submit pediatric data, the Final Rule mandates submission of such data and, most importantly, empowers the USFDA to afford incentives and penalties for non-compliance including possible removal of already marketed products. This overview addresses many of the important components which must be included in the performance of a comprehensive clinical pharmacologic evaluation serving as the foundation for optimal dosing across the broad age range encompassing pediatric practice. Furthermore, the possible risk and/or benefits of the study must be reasonably defined prior to undertaking the study and clearly shared with the patient's caregivers. Consent should always be obtained from the caregiver and, when appropriate, assent obtained from the underage child. To facilitate such clinical investigations and to foster collaborative efforts with innovators and clinical research programs, the National Institutes of Health through the National Institute of Child Health and Human Development of the NIH established a network of Pediatric Pharmacology Research Units. These units have worked closely together and with other pediatric research centers to facilitate USFDA labeling of a number of commonly used medications. All of these very positive efforts highlight the many challenges that remain for the pediatric investigator and practitioner while underscoring the very positive environment in support of these efforts.

Impact of developmental pharmacology on pediatric study design: overcoming the challenges

The need to establish drug-dosing guidelines in children highlights the challenges associated with the development of phases I and II pediatric clinical trials. These challenges are the consequence of significant developmental changes that characterize childhood and adolescence and can affect drug absorption, binding, renal elimination, and, especially, metabolism. In addition, genetic polymorphism can contribute to the variations in the expression of activity for specific drug-metabolizing enzymes. These developmental and genetic variations in pharmacokinetics are the major determinants of drug exposure over time and are thus directly related to the safety, efficacy, and toxicity of a drug dose. Therefore, in the development of pediatric protocols and appropriate dosing in children, it is essential to develop a strategy for addressing the developmental variables that affect drug exposure and to incorporate them into study design.

Incentive to study drugs in children and other governmental initiatives: will patients with asthma benefit?

This article summarizes current regulations that have been developed to facilitate the performance of pediatric drug trials and their impact on children, particularly those children affected with asthma. In addition, other initiatives that have been developed by the federal government in response to the unexplained increase of asthma occurrence during the last 15 years will be reviewed. In the face of an asthma epidemic, a comprehensive approach is needed to determine the causes for the increase in the prevalence rate and the role of aeroallergens and other environmental and genetic factors and to identify effective preventive measures. Clearly, facilitating drug trials to prove the safety and effectiveness of drugs is of paramount importance.

Situations with enhanced chemical risks due to toxicokinetic and toxicodynamic factors

Recognizing toxicokinetic and toxicodynamic variability is important in risk assessment of chemicals and may help to explain interindividual differences in susceptibility in exposed populations. Both toxicokinetic and toxicodynamic factors may be influenced by age and disease processes and show genetic polymorphic variation. Decreased metabolic activity in the very young or very old may enhance chemical toxicity caused by the parent chemical. Similarly, disease processes affecting hepatic metabolism and renal excretion may delay inactivation of many xenobiotics. Genetic polymorphisms may enhance toxicity in rapid metabolizers when the toxicity is caused by a reactive intermediate and increase toxicity in slow metabolizers when the toxicity is caused by a parent chemical. Some cells of the developing conceptus are exquisitely sensitive to chemical exposure. Also, organs and tissues of newborns and elderly individuals may show increased responses toward xenobiotics. In addition, disease-induced altered receptor sensitivity and tissue repair may result in enhanced chemical toxicity. Further, tissue antioxidant defense against radical damage may be compromised under nutritional deficiencies and starvation. Hereditary peculiarities in individual responses to environmental chemicals may be due to polymorphic variation of receptor proteins and tissue repair enzymes, although the database for such variation is quite limited.

Common errors of drug administration in infants: causes and avoidance

Drug administration errors are common in infants. Although the infant population has a high exposure to drugs, there are few data concerning pharmacokinetics or pharmacodynamics, or the influence of paediatric diseases on these processes. Children remain therapeutic orphans. Formulations are often suitable only for adults; in addition, the lack of maturation of drug elimination processes, alteration of body composition and influence of size render the calculation of drug doses complex in infants. The commonest drug administration error in infants is one of dose, and the commonest hospital site for this error is the intensive care unit. Drug errors are a consequence of system error, and preventive strategies are possible through system analysis. The goal of a zero drug error rate should be aggressively sought, with systems in place that aim to eliminate the effects of inevitable human error. This involves review of the entire system from drug manufacture to drug administration. The nuclear industry, telecommunications and air traffic control services all practise error reduction policies with zero error as a clear goal, not by finding fault in the individual, but by identifying faults in the system and building into that system mechanisms for picking up faults before they occur. Such policies could be adapted to medicine using interventions both specific (the production of formulations which are for children only and clearly labelled, regular audit by pharmacists, legible prescriptions, standardised dose tables) and general (paediatric drug trials, education programmes, nonpunitive error reporting) to reduce the number of errors made in giving medication to infants.

The ethical boundaries of drug research in pediatrics

Research abuses in the pediatric setting, mistakes, regulation, minimal investment, and professional misconceptions may contribute to children becoming therapeutic orphans. The moral imperative to expand pediatric pharmacology is urgent but the enterprise is not without risk. Pediatricians as experts in child care are privileged to be able to advocate for the expansion of this invaluable research while simultaneously advocating for the children who are to be involved. In the development of ethical drug research, children's well-being and empowerment can be realized. A shared commitment will help to ensure that in the future we will be better able to provide safe and effective medication and so greatly enhance the care of children.

Noninvasive methods for drug measurement in pediatrics

Infants and children present a special challenge to drug monitoring because the disposition of drugs differs from adults and because there are far fewer clinical studies designed for children than for adults. The excuse for this unfortunate situation is the imposition of severe technical and ethical constraints caused by blood sampling; however, in the past two decades, several new noninvasive methods to measure drugs have been tested and implemented in therapeutic drug monitoring. It is our hope that these new techniques will help advance the ability to diagnose and manage infants and young children.

The receptor occupation and plasma concentration of NKY-722, a water-soluble dihydropyridine-type calcium antagonist, in spontaneously hypertensive rats

1. The occupation in vivo by NKY-722 of 1,4-dihydropyridine (DHP) calcium antagonist receptors in myocardium, aorta and cerebral cortex was investigated. At 1 and 3 h after oral administration of NKY-722 (3 mg kg-1) in spontaneously hypertensive rats (SHR), there was a significant (44 and 41%, respectively) decrease in the number of myocardial (+)-[3H]-PN 200-110 binding sites (Bmax) compared to control values. A greater reduction of Bmax values was observed at 1 (86%), 3 (88%), 6 (63%) and 12 (46%) h later by a higher dose (10 mg kg-1) of this drug. The occupation of myocardial 1,4-DHP calcium antagonist receptors after oral administration of NKY-722 correlated significantly with its plasma concentration. There was a significant decrease in cerebral cortical (+)-[3H]-PN 200-110 binding (Bmax) at 1 and 3 h after oral administration of NKY-722 (10 mg kg-1). 2. Oral administration of nicardipine (10 mg kg-1) in SHR caused a significant reduction of Bmax values for (+)-[3H]-PN 200-110 binding in myocardium at 1 and 3 h later and in cerebral cortex at 1 h later. 3. The in vivo specific binding of (+)-[3H]-PN 200-110 in particulate fractions of aorta of SHR was significantly (79 and 83%, respectively) reduced at 1 and 6 h after oral administration of NKY-722 (3 mg kg-1), while myocardial (+)-[3H]-PN 200-110 binding was decreased by 52% only at 1 h later. Also, nicardipine administration reduced in vivo ( + )-[3H]-PN 200-110 binding in aorta at 1 and 6 h later and in myocardium at 1 h later. On the other hand, the administration of both NKY-722 and nicardipine had no significant effect on in vivo (+ )-[3H]-PN 200-110 binding in cerebreal cortex.4 It is concluded that NKY-722 may exert more selective and sustained occupation in vivo of 1,4-DHP calcium antagonist receptors in vascular tissues of SHR than in myocardial and brain tissues.