Clinical research in neonates and infants: Challenges and perspectives

Pharmacological Research 108 (2016) 80–87

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Pharmacological Research journal homepage: www.elsevier.com/locate/yphrs

Invited review

Clinical research in neonates and infants: Challenges and perspectives Raffaele Coppini a,∗ , Sinno H.P. Simons b , Alessandro Mugelli a , Karel Allegaert c,d a

Department of Neuroscience, Drug Research and Child’s Health (NeuroFarBa), Division of Pharmacology, University of Florence, Italy Department of Pediatrics, Division of Neonatology, Erasmus MC Sophia Children’s Hospital, Rotterdam, The Netherlands c Intensive Care and Department of Pediatric Surgery, Erasmus MC Sophia Children’s Hospital, Rotterdam, The Netherlands d Department of Development and Regeneration, KU Leuven, Belgium b

a r t i c l e

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Article history: Received 26 April 2016 Accepted 26 April 2016 Available online 30 April 2016 Keywords: Pharmacokinetics Pediatrics Pharmacodynamics Aminoglycoside Paracetamol Beta-blockers

a b s t r a c t To date, up to 65% of drugs used in neonates and infants are off-label or unlicensed, as they were implemented in clinical care without the usual regulatory phases of pharmacological drug development. Pharmacotherapy in this age group is still mainly based on the individual clinical expertise of specialized pediatricians. Pharmacological trials involving neonates are indeed more difficult to perform: appropriate dosing is hampered by the rapid physiological changes occurring at this stage of development, and the selection of proper end-points and biomarkers is complicated by the limited knowledge of the pathophysiology of the specific diseases of infancy. Moreover, there are many ethical challenges in planning and conducting drug studies in pediatric patients (especially in newborns and infants). In the current review, we address some challenges and discuss possible perspectives to stimulate scientific and clinical pharmacological research in neonates and infants. We hereby aim to illustrate the add on value of the regulatory framework for model-based neonatal medicinal development currently used in Europe and the United States. We provide several examples of successful recent pharmacological trials performed in neonates and infants. In these examples, success was ensured by the implementation of specific pharmacokinetic assessments, thanks to accurate drug dosing achieved with a combination of dose validation, population pharmacokinetics and mathematical models of drug clearance and distribution; moreover, age-specific pharmacodynamics was considered via appropriate evaluations of drug efficacy with end-points adapted to the peculiar pathophysiology of diseases in this age group. These “pharmacological” challenges add to the ethical challenges that are always present in planning and conducting clinical studies in neonates and infants and support the opinion that clinical research in pediatrics should be evaluated by ad hoc ethical committees with specific expertise. © 2016 Published by Elsevier Ltd.

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Neonatal pharmacological research: current understanding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 Towards evidence-based antibiotic dosing regimens in neonates: a stepwise approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 Cardiovascular drugs and neonatal product development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 3.1. Paracetamol versus ibuprofen for the closure of patent ductus arteriosus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 3.2. Pharmacological treatment of supraventricular tachycardia in infants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 3.3. Disease-modifying treatment of hypertrophic cardiomyopathy in infants with beta-blockers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 Formulations tailored to the characteristics of neonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Future directions of pharmacological research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

1. Neonatal pharmacological research: current understanding ∗ Corresponding author at: Department NeuroFarBa, University of Florence, Viale G. Pieraccini 6, 50139 Florence, Italy. E-mail address: raffaele.coppini@unifi.it (R. Coppini). http://dx.doi.org/10.1016/j.phrs.2016.04.025 1043-6618/© 2016 Published by Elsevier Ltd.

Despite governmental initiatives to stimulate pharmacological research in neonates and infants both in the United States and

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Fig. 1. The currently used regulatory framework is based on specific questions (highlighted in light blue) and results in 3 different types of product development plans (dark blue) for a given compound in neonates.

Europe, the majority of drugs in this pediatric population are still used off-label or unlicensed. In a recent American survey, this mounted up to 65% of the drugs used in Neonatal Intensive Care Units (NICUs) [1]. Similar, in a recent French survey on 8891 prescriptions to 910 NICU neonates, still 5.2% were unlicensed and 59.5% off label. This resulted in exposure to at least one off label or unlicensed drug in 94.8% of these neonates [2]. This is because most of currently used drugs in newborns were implemented in clinical care without the usual regulatory phases of pharmacological drug development. Consequently, neonatal pharmacotherapy is still mainly based on clinical experience, expertise and opinions and is lagging behind when compared to other pediatric subpopulations [3–5]. Because of scientific, regulatory and ethical challenges, trials involving neonates are indeed more difficult to perform. The rapid physiological changes and population specific pathophysiology in the developing neonate affect study design (e.g. dosing, biomarkers, efficacy, endpoints). Protocols and procedures appropriate in adults and older children should not simply be miniaturized to neonates. Lack to consider these issues may in part explain study failures. In a recent survey on 43 drugs studied in neonates between 1998 and 2014 registered in the US Food and Drug Administration databases, 10 drugs were approved based on efficacy data, further supported by pharmacokinetic observations in 4/10 of these drugs [6]. Another 10 drugs were approved based on full (n = 6) or partial (n = 4) extrapolation. Failures were due to inappropriate dose selection (pharmacokinetics) or failure to proof efficacy (maturational pharmacodynamics, biomarkers) [6]. A worldwide collaboration to develop new and existing drugs for neonates has recently been initiated. In a first step, priority conditions required to be studied in this specific population were

identified [7]. Besides the conditions, specific areas – including pharmacokinetic modelling – to facilitate neonatal drug development were described [7]. Because of the extensive variability in physiological characteristics within this pediatric subpopulation, we suggest to use a structured approach to generate robust information on neonatal pharmacotherapy (i.e. “pharmacometrics”, see below). In the current review, we want to address some challenges and discuss possible perspectives to stimulate scientific and clinical research. We hereby aim to illustrate the add on value of the regulatory framework for model-based neonatal medicinal development currently used in Europe and the United States (Fig. 1) [8]. Questions on the similarity between neonates and other populations on disease evolution, response to intervention, concentration-response and pharmacodynamic measurement (biomarkers) drive the study decision tree to result in 3 different types of product development programs. The relevance of this decision tree will be illustrated for antibiotics and cardiovascular drugs (Fig. 1). 2. Towards evidence-based antibiotic dosing regimens in neonates: a stepwise approach When applying the decision tree (Fig. 1) for aminoglycosides, it seems reasonable to postulate similarities (disease evolution, response to intervention and concentration-response) and consequently, to focus on PK (aim for levels similar to other populations) and safety studies. Development of an evidence-based individual dosing regimen by population pharmacokinetic modelling is optimally achieved using a structured approach, based on (step a) optimal study design based on data gathering during drug use in clinical practice, (step b) development and internal validation of

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Fig. 2. Stepwise approach for dose regimen development and validation for antibiotics, assuming that only maturational pharmacokinetics should be considered.

the model, including dosing regimen suggestions based on the relevant covariates and using target concentrations, (step c) prospective validation of the dosing regimen in the clinical reality, (step d) feedback and optimalisation of dosages (Fig. 2) [9]. In the newborn, this means that weight (e.g. birth weight, current weight) and indicators of maturation (gestational age, postnatal age, postmenstrual age) are the most relevant covariates of renal drug clearance. These covariates already result in extensive variability. This between and within-individual variability is further aggravated by pathophysiologic characteristics (e.g. growth restriction, renal failure, perinatal asphyxia), medical interventions (e.g. whole body cooling, extra corporeal membrane oxygenation) or co-medication (e.g. drugdrug interactions, population specific toxicity like for ibuprofen or indomethacin) [10]. We would like to illustrate the strength of such a structured approach by consecutive studies on amikacin pharmacokinetics (PK) in neonates. Like any other aminoglycoside, bactericidal effectiveness of amikacin relates to peak concentrations, while toxicity relates to the average or trough concentration. These targets resulted in the concept to administer higher doses with extended dosing intervals. Since aminoglycoside clearance reflects glomerular filtration rate (GFR), it is to be anticipated that maturational clearance displays a continuum that cannot be covered by simple (e.g. one dose fits all, dichotomous) dosing regimen [11]. In a first step, population pharmacokinetic modelling was performed using data from 874 neonates obtained from clinical observations in two earlier published datasets [12]. In these cohorts, the dosing regimen was easy (20 mg/kg every 36 h or 24 h in preterm neonates <30 weeks of postmenstrual age or not respectively), but not accurate [i.e. target peak (>24 mg/L), mainly though values (<3 mg/L)]. The influence of age, weight and other covariates was investigated in this dataset (step b). Amikacin clearance in neonates related to weight at birth, reflecting maturation of glomerular filtration rate (GFR) until birth, and postnatal age (days) and co-administration of ibuprofen, reflecting postnatal covariates of GFR (step a) [12,13]. Using these covariates, a dosing regimen was suggested based on 5 different birth weight categories (<800 g, 800–1200 g, 1200–1800 g, 1800–2800 g and >2800 g), postnatal age (dichotomous, 14 days) and ibuprofen exposure (yes/no, prolongation time interval +10 h) (step b) [13]. This amikacin dosing regimen was subsequently prospectively validated using 1195 therapeutic drug monitoring observations in 579 neonates (step c). Overall, target peak (>24 mg/L) and trough values (<3 mg/L) were attained in

most patient groups [14]. Specific subgroups (>2000 g and <14 days postnatal life) who would benefit from an additional dosing adaptation were identified and optimised (step d). Consequently, this first prospective validation effort ended with the proposal of a new, improved dosing regimen, which in turn underwent subsequent evaluation, resulting in a final, validated dosing regimen [14]. Prospective validation is crucial, but uncommon. Wilbaux et al. [15] recently summarized the available population PK data and models for primarily renally eliminated antibiotics in neonates. This systematic search resulted in 61 articles published between 1984 and 2015 with PK data on 13 different antibiotics. Unfortunately, only 51% of the studies reported on advanced internal validation procedures, and only 20% of these studies used external validation methods [15]. This absence of validation efforts likely also explains the high variability in dosing of commonly used antibiotics, as revealed by a Europe-wide point prevalence study [16]. Two additional issues are worth to be mentioned. First, once a PK model has been built based on an extensive dataset of observations in neonates, these models can be used to develop evidence based dosing regimens of specific subpopulations of neonates (‘pharmacometrics’) like e.g. (near) term neonates undergoing whole body cooling after moderate to severe perinatal asphyxia [17] (Fig. 2). To illustrate this, a recent paper on gentamicin pharmacokinetics in term neonates undergoing controlled hypothermia provided evidence for an increase in clearance of 30% after rewarming (>72 h of postnatal age), but this covariate displays collinearity with postnatal age [18]. We suggest that a structured stepwise approach has the potential to provide more robust evidence to guide pharmacotherapy [9]. Second, since amikacin clearance reflects glomerular filtration rate (GFR), it is very reasonable to apply the same maturational GFR model to dosing suggestions for other drugs cleared by renal elimination like netilmicin, gentamicin, tobramycine or even vancomycin, hereby including the drug specific target concentrations (peak, trough or median concentration/area under the curve) [11,19]. The amikacin model is hereby used as a semi-physiological GFR function to facilitate step a and b for other compounds, including gentamicin, tobramycin and vancomycin [20,21] or future drugs in newborns (Fig. 2). Obviously, subsequent prospective validation is still needed, but such an approach turns neonatal

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pharmacology from exploratory into hypothesis driven clinical research. 3. Cardiovascular drugs and neonatal product development In contrast to the aminoglycoside example, the neonatal product development for cardiovascular drugs is more complicated. This is because the disease is specific to neonates (e.g. patent ductus arteriosus) or has pathophysiological characteristics specific in neonates (e.g. supraventricular tachycardia, hypertrophic cardiomyopathy). Consequently, compound and indication specific studies should consider potential maturational concentrationresponse curves, followed by PK studies based on this target concentration to document efficacy, and safety studies (Fig. 1). 3.1. Paracetamol versus ibuprofen for the closure of patent ductus arteriosus A nice illustration on the specificities and difficulties to perform pharmacological clinical studies in neonates is the recent work where the commonly used ibuprofen regimen for the closure of a patent ductus arteriosus (PDA) is compared with paracetamol. PDA is a clinical condition in preterm infants and relates inversely to birth weight and gestational age. Cyclooxygenase (COX) inhibitors such as indomethacin and ibuprofen are the most commonly used drugs for PDA closure. Even in the absence of head to head studies, ibuprofen is considered to be the first choice due to its better safety profile when compared to indomethacin, as it is associated with fewer gastrointestinal and renal side effects [22,23]. PDA closure rates are higher with oral than with intravenous ibuprofen probably due to the concentration-time profiles of the drug and subsequent suppression of prostaglandins [24]. Ibuprofen was reported to be associated with several adverse effects including transient renal impairment, gastrointestinal bleeding and perforation, hyperbilirubinemia and platelet dysfunction [25]. Recent works suggest that paracetamol could be a valid alternative to ibuprofen for PDA closure having less adverse events and side effects [23,26,27]. The first case reports showed a very high rate of ductal closure in preterm newborns treated with intravenous paracetamol [28]. Since these observations, two open label trials studied the effect of paracetamol on PDA closure in a total of 250 infants. In the first study [29], 160 preterm infants (median 31 weeks gestational age) with ultrasound-confirmed PDA were randomly assigned to receive either ibuprofen or a high dose of oral paracetamol (15 mg/kg every 6 h for 3 days). The rate of PDA closure was around 80% with both drugs, with no significant differences. The second randomized study [30] enrolled 90 preterm (<30 weeks, birth weight <1250 g) infants and confirmed the equivalence of oral paracetamol and ibuprofen in terms of rate of PDA closure. This trial was far too small to detect important yet uncommon adverse effects of paracetamol. We would like to stress the need for further research concerning the mechanism, the efficacy and safety of paracetamol before robust recommendations can be provided [31]. Even if the mechanism of action of paracetamol in determining ductal closure remains unclear, the clinical studies in neonates have contributed to change our mind concerning its mode of action. The “old” hypothesis of a selective inhibition of brain-specific COX-3 by paracetamol has been rejected [32–34]. Paracetamol inhibits COX-2 and COX-1 by blocking the peroxidase function of these isoenzymes, especially when low levels of arachidonic acid and peroxides are available. Conversely, it has little activity at substantial levels of arachidonic acid and peroxides, e.g. in inflammatory tissue. This, combined with its ability to easily cross the blood brain barrier, explains why paracetamol exerts a marked inhibition of

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brain COX enzymes. Moreover, paracetamol shows some selectivity for COX-2 and therefore is unable to achieve the >90% inhibition of platelet COX-1 that is necessary for an active anti-platelet effect. However, paracetamol exerts a sufficient inhibitory effect on constitutive vascular COX enzymes to justify its PDA-closing ability, although at a relatively high concentration. Detailed studies on COX vascular isoenzyme expression in neonates and their changes in the first weeks of life remain to be accomplished. Laser Doppler imaging to detect microcirculatory perfusion changes [35] could generate additional information to understand the mechanisms of action in PDA closure for both ibuprofen and paracetamol. While paracetamol used in analgesic dosages appears to be safer than ibuprofen, insufficient data exists on the safety of paracetamol when used at 60 mg/kg/day in extreme preterm (<28 weeks) neonates. Paracetamol pharmacokinetics has been extensively studied in preterm neonates treated for “common” indications (pain, fever) with a dose of 8–10 mg/kg every 6 h. With the aforementioned dose, a compartment concentration of 11 mg/L is reached, which is effective in controlling pain and lowering fever without leading to a significant increase in liver enzymes, and with limited effects on blood pressure or heart rate [36]. In contrast, the higher doses suggested (60 mg/kg/day) in extreme preterm neonates to induce PDA closure have not yet been sufficiently evaluated regarding either efficacy or safety. Animal experimental studies do provide some evidence for the need of a cautious approach. A recent study in mice documented severe adverse effects on the developing brain from paracetamol administered in neonates, including cognitive deficit and behavioral alterations in adult animals [37]. These animal experimental observations are further supported by observations on a weak but significant association between prenatal paracetamol exposure and the development of autism or autism spectrum disorder in childhood [38,39]. Furthermore, a link between early paracetamol exposure and development of food allergy in children has been suggested [40]. For these reasons, long-term follow-up to at least 18–24 months postnatal age must be incorporated in any study on paracetamol. As a final illustration on the PDA topic, we want to refocus on the need to perform PK studies and to reconsider dosing once clinical practices change. The efficacy of ibuprofen was shown in 1996 by Varvarigou who showed that a 10 mg ibuprofen per kg on the first day of life, repeated by a 5 mg/kg on the second and third day was more effective to close the PDA than a single dose on day 1 or normal saline [41]. Afterwards ibuprofen was implemented worldwide. However, based on a shift in patent ductus management, many clinicians started to use the drug at older postnatal ages, but still using the same dosages despite the fact that PK research showed that ibuprofen clearance increased significantly with postnatal age and [42]. In the absence of a PK model validation study, postnatal age dependent ibuprofen dosages have not yet been implemented. Ibuprofen dose optimalisation and validation is needed before any further comparative trial with ibuprofen is started. 3.2. Pharmacological treatment of supraventricular tachycardia in infants Supraventricular tachycardia (SVT) is a common pediatric condition affecting 1:250–1:1000 infants and children [43]. The mechanism causing SVT, as determined by trans-esophageal electrophysiologic studies, involves an accessory pathway in more than 75% of infants, atrioventricular (AV) node reentry in 10%, atrial muscle re-entry in 10%, and an ectopic atrial tachycardia in 5% of affected subjects [44]. Approximately 60% of children with supraventricular tachycardia (SVT) develop their initial episode by 1 year of age. Despite resolution by 1 year in most of these patients, approximately 30% of the SVT will recur, and the rate of recur-

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rence is 10 times higher in subjects with ventricular pre-excitation (Wolf-Parkinson-White, WPW) [44]. Catheter ablation therapy has largely replaced medical treatment for older children with symptomatic SVT. Contrarily, pharmacologic therapy is still the therapy of choice for newborns and infants with SVT [45]. Despite its frequency, there is only limited evidence to guide SVT treatment. A survey in North America showed that the most commonly used drugs in infants with acute SVT were digoxin and propranolol, used respectively in patients without or with ventricular pre-excitation [46]. Digoxin and propranolol were the most frequently prescribed agents, also in the chronic setting. Interestingly, the only significant association with the selected drug was the background of the prescribing clinician: general pediatric cardiologists tended to prescribe digoxin, while trained electrophysiologists favored propranolol. In 2012, Sanatani et al. reported on a randomized double-blind trial to compare the efficacy and safety of digoxin and propranolol for antiarrhythmic prophylaxis of SVT in infants below four months of age without WPW [47]. Taking also the limited number of recruited patients (n = 61) into account, no difference in SVT recurrence in infants treated with digoxin versus propranolol was observed. A subsequent retrospective cohort study in about 500 infants with SVT treated with either digoxin or propranolol suggested different effect/safety profiles for both compounds. While treatment failure was higher on propranolol (hazard ratio 1.97), digoxin resulted in a higher incidence of symptomatic hypotension [48]. However, the differences in outcome and risk of side effects between the two medications is likely to be very small, as another similar database study did not find any differences in the rate of success between digoxin and propranolol [49]. Again, developmental pharmacology, both PK and PD should be considered. The propranolol dose for SVT control in infants must be adjusted to be effective at this age. Indeed, a relatively high dose of propranolol (>3.5 mg/kg/day) was found to be safe and effective in infants with SVT, while lower doses were only partially effective in preventing arrhythmias [50]. The antiarrhythmic action of digoxin on supraventricular arrhythmias in infants is mainly related with its electrophysiological effects on atrio-ventricular (AV) node cells. Due to increase intracellular Ca2+ concentration, digoxin increases the electrical refractory period of nodal cells, leading to slower intranodal conduction. Owing to the potentiation of cardiac parasympathetic tone, digoxin slows down nodal spontaneous firing rate [51,52]. Supraventricular arrhythmias in infants are prevalently determined by large reentry circuits often involving nodal conduction. Therefore, in this age group digoxin not only reduces ventricular rate during runs of SVT, but also prevents the recurrence of arrhythmias. This is a reflection of age-specific pharmacodynamics. Because of its narrow therapeutic index, the occurrence of adverse drug reactions is common [53]. Population pharmacokinetics approaches have been used in this pediatric subgroup in order to assess the clearance of digoxin and its relationship with age, body weight and other clinical conditions (e.g. the presence of heart failure). Such studies led to the validation of specific formulas to adjust the dose of digoxin according to several covariates [54,55], although these are complex to be routinely used in the clinical setting. The changes in digoxin clearance in newborns, infants and older children are an excellent example of the maturation of renal tubular excretion activity [56]. Digoxin is excreted by glomerular filtration, but also extensively secreted by the tubular renal cell Pglycoprotein. Young children need 3-times higher doses of digoxin per kg of body weight as compared with adults. This difference cannot only be explained by changes in GFR [57]. Indeed, GFR in young children is only 2-times higher than in adults per kg.

3.3. Disease-modifying treatment of hypertrophic cardiomyopathy in infants with beta-blockers The pharmacological treatment of hypertrophic cardiomyopathy is another illustration of the obvious need to consider both PK, PD and the concentration-response profile in neonates (Fig. 1). Infants with hypertrophic cardiomyopathy (HCM) present with diastolic dysfunction, resulting in very high left-ventricular filling pressures [58], eventually leading to pulmonary and systemic congestion. When HCM presents with heart failure in infancy, the prognosis is very poor unless the condition is promptly treated. Early studies described 100% mortality among infants with HCM and CHF (congestive heart failure) presenting below 1 year of age, when treated with a standard therapeutic strategy comprising digoxin and/or diuretics [59]. Interestingly, high-dose propranolol treatment was associated with long-term survival in a case of a HCM patient with symptomatic presentation in the first year of life [60]. A similar approach was followed by Östman-Smith and colleagues, who reported a significant improvement of survival in infants and children with hypertrophic cardiomyopathy, with both idiopathic/familial HCM, and HCM associated with Noonan/Leopard/Costello syndromes [61]. This pharmacotherapy was based on the postulation that HCM was notably associated with increased sympathetic nervous activity [62] and cardiac hypertrophy in animal models of cardiac hypertrophy was found to be reduced by beta-adrenoceptor blockade [63]. The improved survival by beta-blocker treatment was due to a reduction both in early-onset heart-failure and in later-stage arrhythmic suddendeaths [61]. Subsequently, Skinner et al. reported that, in a consecutive series of infants with HCM, survivors were treated with beta-blocker drugs, while none of the patients who died had received beta-blockers [64]. In hospitals where the policy of treating all HCM with pediatric presentation with beta-blockers, the survival rate at 15 years was 82% [65], a very good result when compared with the 60% 5-year survival in childhood HCM patients treated with conventional therapies. The mechanisms by which beta-blockers are effective in HCM are multiple: beta-blockers reduce outflow tract obstruction by lowering pressure gradient, significantly improve diastolic function by prolonging diastolic time [66], and may also exert beneficial effects on disease progression, i.e. reducing or preventing the development of severe LV hypertrophy. The idea of preventing the manifestation of HCM by early initiation of pharmacological treatment in pre-symptomatic young mutation-carriers is being pursued in animal models using the late Na-current blocker ranolazine [67,68]. Interestingly, disease-modifying effects of betablockers in HCM appear to be present only in childhood HCM, as beta-blockers were never proven to be capable of increasing survival or reducing disease progression in adult HCM patients treated with standard dosage [69]. Again, this suggest population specific pharmacodynamics, but there are also important observations on a concentration-response relationship. When treating HCM infants with beta-blockers, the dose range employed is extremely important. If patient mortality is analyzed in cohorts of pediatric HCM patients receiving different doses of propranolol-equivalent, yearly mortality due to cardiac causes was 4% with 1–2 mg/kg/day, 1.8% with 2–5.9 mg/kg/day, and 0.6% when 6 mg/kg/day and above were used [70]. Such doses are very high when compared with those used in adults, where 2 mg/kg/day is the generally recommended dose. However, such high dose requirement can be explained by the pharmacokinetics of beta-blockers in infancy and childhood. For example, the clearance of carvedilol (metabolized by the same enzymes as propranolol) was found to be nearly 4 times faster in 1-year old infants when compared with 19-year old adults. Thus, infants require a 4 times higher weight-adjusted dose to maintain

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similar plasma levels as adults [71]. Infants in heart failure sometimes require doses of 20 mg/kg/day or higher in order to achieve effective beta-blockade. Since the activity of cardiac sympathetic nerves is pathologically increased in HCM, leading to higher circulating catecholamine levels [72], pediatric patients with HCM often require a higher dose of beta-blocker when compared with age-matched patients with different conditions. In this condition, it is very hard to target a specific dose in mg/kg, because of the large variability of drug clearance among different patients due to enzyme polymorphisms [73] and variable degrees of hepatic maturation [74]. The most feasible approach is to judge the individual beta-blocker dose based on the physiological response in each patient. For the purpose of treating childhood HCM, we need a high degree of beta-blockade, with a near abolishment of heart rate variability during the day. This can be easily ascertained by using long-term ECG monitoring (e.g. 24 h Holter ECG). In an infant presenting with CHF the starting oral dose of propranolol is 2 mg/kg four times daily, to be subsequently increased if the effect is insufficient. The serum concentrations of propranolol required in childhood patients with HCM is 200–900 ␮g/L, but in infants with CHF we need to reach concentrations up to 1100 ␮g/L. The side effects of beta-blockers are surprisingly rare in infants with CHF due to HCM, even at such high doses. No issues of impaired or delayed development were ever reported. The only potential serious side effect is hypoglycemia after prolonged fasting. In conclusion, beta-blockers are the drugs of choice to treat HCM occurring in infancy, though the dose needs to be carefully titrated to achieve the maximum benefit. We hereby provided an illustration of maturational PK, PD and population specific concentration-response profiles.

4. Formulations tailored to the characteristics of neonates Formulations are the final medicinal product in which different chemical substances, including the active compound, but also excipients. Neonates deserve formulations that are adapted to their needs. Since the key characteristics of neonatal pharmacology is the extensive variability despites the overall low elimination capacity, this should be translated to drug formulations with low, adjustable and flexible dosing to maintain dose accuracy. Unfortunately, neonates are still commonly treated with formulations that have not been designed, developed nor evaluated for use in this population [75,76]. The challenges associated with the different routes of administration (e.g. oral, parenteral, but also transdermal, intrapulmonary or rectal) in neonatal drug delivery have recently been summarized [77]. We hereby would like to highlight two aspects, i.e. dose accuracy (repeated dilution) and the issue of excipients (maturational toxicology). There is a risk that manipulation introduces an additional error when calculating or preparing doses and results in inaccuracy (too low, too high, or too variable dose) with potential additional effects on e.g. stability and bioavailability [75,76]. In an attempt to quantify the impact of a tailored vial, the introduction of a pediatric amikacin vial (50 mg/ml instead of a 250 mg/ml vial) resulted in a reduction in clearance variability in a cohort of (pre) term neonates, reflecting improved dosing precision [78]. Recently, Campino et al. quantified the impact of protocol standardization and education on the medicine preparation (calculation errors from 1.35 to 0%; accuracy errors from 54.7 to 23%) error rate in 10 Spanish NICU’s. Since the definition for accuracy was 90–110% of the intended concentration, 23% reflects progress, but with still potential for improvement in formulations [79]. During the development of such formulations, there is also a need for more guidance on excipient exposure in neonates [75]. Besides the active compounds, drug formulations may also contain

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excipients as co-solvents, preservatives, sweeteners or colorants. Examples of such excipients are lactose, aspartame, xylitol, propylene glycol, poly-ethylene glycol, benzyl alcohol, ethanol, sorbitol or mannitol [75]. In a recent European survey in 89 NICU’s and 726 neonates, potential harmful excipients (parabens, polysorbate 80, propylene glycol, benzoates, saccharin sodium, sorbitol, ethanol, benzalkonium chloride) were retrieved in 31% of the prescriptions and administered to 63% of admitted neonates on a given day. Regional differences in formulations were hereby observed, suggesting that excipient-free products exist, are marketed and may provide an opportunity to avoid excipient exposure [80]. Another strategy is the development of other dose-flexible formulations, like uncoated mini-tablets as the acceptability of these mini-tablets has recently been proven to be similar to syrup in neonates [81]. Finally, efforts have been made for knowledge building through database building (e.g. Safety and Toxicity of Excipients for Pediatrics [STEP] database initiative) [75]. Along this initiative, population focussed studies on aspects of clinical pharmacology of excipients in neonates were conducted to fill knowledge gaps for propylene glycol or parabens [82–84].

5. Future directions of pharmacological research In this overview we suggest several directions for future pharmacological research in newborns. We hereby stressed the use of the regulatory framework (Fig. 1) to reflect about neonatal drug development programs. The example of amikacin, where clinical data on efficacy, safety and PK were gathered, population modelling provided new dosage regimen suggestions that were prospectively validated and optimised, illustrates an elegant way to obtain adequate dosing schedules for newborns. These dosing regimen take important covariates into account such as age, co-medication, etc. This strategy can be simplified for future drug research using ‘pharmacometrics’, where the specific developmental properties that determine PK/PD, such as solubility, renal clearance and metabolic pathway, can be used as a basis to predefine the important covariates and to predict dosing regimen. Overall, impressive progress has been made in the field of developmental PK and its modelling. The next steps to take in neonatal clinical pharmacology are the development and validation of pharmacodynamic measurements (‘biomarkers’), comparison of different drugs using long term neonatal outcome and better assessment and registration of sideeffects and safety. Current pharmacodynamic outcome parameters often are subjective and effects of drugs are poorly registered in neonatal intensive care. Improved data collection and analyses of continuous physiological parameters, including heart rate variability, near infrared spectroscopy and a EEG might provide better pharmacodynamic effect registration. Randomised controlled trials that compared drugs using inadequate dosing, i.e. before PK/PD modelling and validation, might need to be repeated if dosages turn out to be inappropriate. Finally, a very important point of neonatal drug use improvement can be found in better pharmacovigilance, focused on efficacy and safety. The realisation of international sideeffect registration databases would be very helpful for this aim and this is one of the aims of the earlier mentioned INC research consortium [85]. Irrespective of the topics earlier discussed, the ethical aspects of conducting clinical studies in neonates should also be considered as it has been recently highlighted [86]. In our opinion, the specificity of clinical research in neonates and infants (but possibly in the pediatric population in general) make necessary that “ad hoc” ethical committees, with specific expertise and knowledge of these challenges, should be instituted: this is especially so since the new Clinical Trials Regulation (CTR) EU No 536/2014 will become applicable in the

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next future (http://ec.europa.eu/health/human-use/clinical-trials/ regulation/index en.htm) with the aim to favour clinical reaserch in Europe and to speed up the process of evaluation and approval.

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Acknowledgements

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The clinical research activities of Karel Allegaert were supported by the Fund for Scientific Research, Flanders (fundamental clinical investigatorship 1800214N), further facilitated by the agency for innovation by Science and Technology in Flanders (IWT) through the SAFEPEDRUG project (IWT/SBO 130033). The clinical research activities of Sinno Simons were supported by a Clinical Fellowship of the Netherlands Organization for Health Research and Innovation (ZonMW 90713494). The work of Dr. Raffaele Coppini was supported by Telethon Italy (GGP13162) and by the Italian Ministry of Health (GR-201102350583). Neither Raffaele Coppini, Sinno Simons or Alessandro Mugelli have any potential conflict of interest related to the content of this paper. Alessandro Mugelli is chairing the Pediatrics Ethics Committee of the Tuscany Region, Italy.

[19]

[20]

[21]

[22]

[23]

[24]

References [25] [1] E.M. Hsieh, C.P. Hornik, R.H. Clark, et al., Medication use in the neonatal intensive care unit, Am. J. Perinatol. 31 (2014) 811–822, http://dx.doi.org/10. 1055/s-0033-1361933. [2] S. Riou, F. Plaisant, D.M. Boulch, B. Kassai, O. Claris, K.A. Nguyen, Unlicensed and off-label drug use: a prospective study in French NICU, Acta Paediatr. 104 (2015) e228–e231, http://dx.doi.org/10.1111/apa.12924. [3] M.M. Laughon, D. Avant, N. Tripathi, et al., Drug labeling and exposure in neonates, JAMA Pediatr. 168 (2014) 130–136, http://dx.doi.org/10.1001/ jamapediatrics.2013.4208. [4] J.L. Stiers, R.M. Ward, Newborns, one of the last therapeutic orphans to be adopted, JAMA Pediatr. 168 (2014) 106–108, http://dx.doi.org/10.1001/ jamapediatrics.2013.4604. [5] K. Allegaert, J. van den Anker, Neonatal drug therapy: the first frontier of therapeutics for children, Clin. Pharmacol. Ther. 98 (2015) 288–297, http://dx. doi.org/10.1002/cpt.166. [6] J. Wang, D. Avant, D. Green, et al., A survey of neonatal pharmacokinetic and pharmacodynamic studies in pediatric drug development, Clin. Pharmacol. Ther. 98 (2015) 328–335, http://dx.doi.org/10.1002/cpt.149. [7] J.M. Davis, M.A. Turner, Global collaboration to develop new and existing drugs for neonates, JAMA Pediatr. 169 (2015) 887–888, http://dx.doi.org/10. 1001/jamapediatrics.2015.1640. [8] E. Manolis, G. Pons, Proposals for model-based paediatric medicinal development within the current European Union regulatory framework, Br. J. Clin. Pharmacol. 68 (2009) 493–501, http://dx.doi.org/10.1111/j.1365-2125. 2009.03484.x. [9] R. Admiraal, C. van Kesteren, J.J. Boelens, R.G.M. Bredius, D. Tibboel, C.A.J. Knibbe, Towards evidence-based dosing regimens in children on the basis of population pharmacokinetic pharmacodynamic modelling, Arch. Dis. Child. 99 (2014) 267–272, http://dx.doi.org/10.1136/archdischild-2013-303721. [10] J. Samardzic, K. Allegaert, M. Wilbaux, M. Pfister, J.N. van den Anker, Quantitative clinical pharmacology practice for optimal use of antibiotics during the neonatal period, Expert Opin. Drug Metab. Toxicol. 12 (2016) 367–375, http://dx.doi.org/10.1517/17425255.2016.1147559. [11] W. Zhao, V. Biran, E. Jacqz-Aigrain, Amikacin maturation model as a marker of renal maturation to predict glomerular filtration rate and vancomycin clearance in neonates, Clin. Pharmacokinet. 52 (2013) 1127–1134, http://dx. doi.org/10.1007/s40262-013-0101-6. [12] R.F.W. De Cock, C. Piana, E.H.J. Krekels, M. Danhof, K. Allegaert, C.A.J. Knibbe, The role of population PK-PD modelling in paediatric clinical research, Eur. J. Clin. Pharmacol. 67 (2011) S5–S16, http://dx.doi.org/10.1007/s00228-0090782-9. [13] R.F.W. De Cock, K. Allegaert, M.F. Schreuder, et al., Maturation of the glomerular filtration rate in neonates, as reflected by amikacin clearance, Clin. Pharmacokinet. 51 (2012) 105–117. [14] A. Smits, R.F.W. De Cock, K. Allegaert, S. Vanhaesebrouck, M. Danhof, C.A.J. Knibbe, Prospective evaluation of a model-Based dosing regimen for amikacin in preterm and term neonates in clinical practice, Antimicrob. Agents Chemother. 59 (2015) 6344–6351, http://dx.doi.org/10.1128/aac.01157-15. [15] M. Wilbaux, A. Fuchs, J. Samardzic, et al., Pharmacometric approaches to personalize use of primarily renally eliminated antibiotics in preterm and term neonates, J. Clin. Pharmacol. (2016), http://dx.doi.org/10.1002/jcph.705. [16] T. Metsvaht, G. Nellis, H. Varendi, et al., High variability in the dosing of commonly used antibiotics revealed by a Europe-wide point prevalence

[26]

[27] [28]

[29]

[30]

[31]

[32]

[33]

[34]

[35]

[36]

[37]

[38]

[39]

[40]

study: implications for research and dissemination, BMC Pediatr. (2015) 15, http://dx.doi.org/10.1186/s12887-015-0359-y (ARTN 41). P. Pokorna, E.D. Wildschut, V. Vobruba, J.N. van den Anker, D. Tibboel, The impact of hypothermia on the pharmacokinetics of drugs used in neonates and young infants, Curr. Pharm. Des. 21 (2015) 5705–5724, http://dx.doi.org/ 10.2174/1381612821666150901110929. Y.A. Bijleveld, T.R. de Haan, J.H. van der Lee, et al., Altered gentamicin pharmacokinetics in term neonates undergoing controlled hypothermia, Br. J. Clin. Pharmacol. (2016), http://dx.doi.org/10.1111/bcp.12883. R.F.W. De Cock, K. Allegaert, C.M.T. Sherwin, et al., A neonatal amikacin covariate model can Be used to predict ontogeny of other drugs eliminated through glomerular filtration in neonates, Pharm. Res. Dordr. 31 (2014) 754–767, http://dx.doi.org/10.1007/s11095-013-1197-y. E.J.H. Janssen, P.A.J. Valitalo, K. Allegaert, et al., Towards rational dosing algorithms for vancomycin in neonates and infants based on population pharmacokinetic modeling, Antimicrob. Agents Chemother. 60 (2016) 1013–1021, http://dx.doi.org/10.1128/aac.01968-15. P.A.J. Valitalo, J.N. van den Anker, K. Allegaert, et al., Novel model-based dosing guidelines for gentamicin and tobramycin in preterm and term neonates, J. Antimicrob. Chemoth. 70 (2015) 2074–2077, http://dx.doi.org/10. 1093/jac/dkv052. A. Ohlsson, R. Walia, S. Shah, Ibuprofen for the treatment of patent ductus arteriosus in preterm and/or low birth weight infants, The Cochrane database of systematic reviews, 2008, CD003481, 10.1002/14651858, CD003481, pub3. A. Ohlsson, R. Walia, S.S. Shah, Ibuprofen for the treatment of patent ductus arteriosus in preterm or low birth weight (or both) infants, The Cochrane database of systematic reviews, 2015, 2, CD003481, 10.1002/14651858, CD003481, pub6. R. Neumann, S.M. Schulzke, C. Buhrer, Oral ibuprofen versus intravenous ibuprofen or intravenous indomethacin for the treatment of patent ductus arteriosus in preterm infants: a systematic review and meta-analysis, Neonatology 102 (2012) 9–15, http://dx.doi.org/10.1159/000335332. M.Y. Oncel, O. Erdeve, Oral medications regarding their safety and efficacy in the management of patent ductus arteriosus, World J. Clin. Pediatr. 5 (2016) 75–81, http://dx.doi.org/10.5409/wjcp.v5.i1.75. A. Ohlsson, P.S. Shah, Paracetamol (acetaminophen) for patent ductus arteriosus in preterm or low-birth-weight infants, The Cochrane database of systematic reviews, 2015, 3, CD010061, 10.1002/14651858, CD010061, pub2. M.Y. Oncel, O. Erdeve, Safety of therapeutics used in management of patent ductus arteriosus in preterm infants, Curr. Drug Saf. 10 (2015) 106–112. M.Y. Oncel, S. Yurttutan, H. Degirmencioglu, et al., Intravenous paracetamol treatment in the management of patent ductus arteriosus in extremely low birth weight infants, Neonatology 103 (2013) 166–169, http://dx.doi.org/10. 1159/000345337. D. Dang, D. Wang, C. Zhang, W. Zhou, Q. Zhou, H. Wu, Comparison of oral paracetamol versus ibuprofen in premature infants with patent ductus arteriosus: a randomized controlled trial, PLoS One 8 (2013) e77888, http:// dx.doi.org/10.1371/journal.pone.0077888. M.Y. Oncel, S. Yurttutan, O. Erdeve, et al., Oral paracetamol versus oral ibuprofen in the management of patent ductus arteriosus in preterm infants: a randomized controlled trial, J. Pediatr. 164 (2014) 510, http://dx.doi.org/10. 1016/j.jpeds.2013.11.008. K. Allegaert, B. Anderson, S. Simons, B. van Overmeire, Paracetamol to induce ductus arteriosus closure: is it valid? Arch. Dis. Child. 98 (2013) 462–466, http://dx.doi.org/10.1136/archdischild-2013-303688. B.J. Anderson, Paracetamol (Acetaminophen): mechanisms of action, Paediatr. Anaesth. 18 (2008) 915–921, http://dx.doi.org/10.1111/j.1460-9592.2008. 02764.x. G.G. Graham, M.J. Davies, R.O. Day, A. Mohamudally, K.F. Scott, The modern pharmacology of paracetamol: therapeutic actions, mechanism of action, metabolism, toxicity and recent pharmacological findings, Inflammopharmacology 21 (2013) 201–232, http://dx.doi.org/10.1007/ s10787-013-0172-x. B. Hinz, O. Cheremina, K. Brune, Acetaminophen (paracetamol) is a selective cyclooxygenase-2 inhibitor in man, FASEB J. 22 (2008) 383–390, http://dx.doi. org/10.1096/fj.07-8506com. P. Erba, P. Harbi, T. Thacher, A. Pries, G. Ambrosio, W. Raffoul, Early detection of microcirculatory perfusion changes with a high resolution, real time laser Doppler imaging camera–frostbite case study, BMJ Case Reports 2011 (2011), http://dx.doi.org/10.1136/bcr.06.2011.4404. G.M. Pacifici, K. Allegaert, Clinical pharmacology of paracetamol in neonates: a review, Curr. Ther. Res. Clin. Exp. 77 (2015) 24–30, http://dx.doi.org/10. 1016/j.curtheres.2014.12.001. H. Viberg, P. Eriksson, T. Gordh, A. Fredriksson, Paracetamol (Acetaminophen) administration during neonatal brain development affects cognitive function and alters its analgesic and anxiolytic response in adult male mice, Toxicol. Sci. 138 (2014) 139–147, http://dx.doi.org/10.1093/toxsci/kft329. Z. Liew, B. Ritz, J. Virk, J. Olsen, Maternal use of acetaminophen during pregnancy and risk of autism spectrum disorders in childhood: a Danish national birth cohort study, Autism Res.: Off. J. Int. Soc. (2015), http://dx.doi. org/10.1002/aur.1591. Z. Liew, B. Ritz, C. Rebordosa, P.C. Lee, J. Olsen, Acetaminophen use during pregnancy, behavioral problems, and hyperkinetic disorders, JAMA Pediatr. 168 (2014) 313–320, http://dx.doi.org/10.1001/jamapediatrics.2013.4914. J.P. Langhendries, K. Allegaert, J.N. Van den Anker, F. Veyckemans, F. Smets, Possible effects of repeated exposure to ibuprofen and acetaminophen on the

R. Coppini et al. / Pharmacological Research 108 (2016) 80–87

[41]

[42]

[43]

[44]

[45]

[46]

[47]

[48]

[49]

[50]

[51]

[52]

[53] [54] [55]

[56]

[57]

[58] [59] [60]

[61]

[62]

intestinal immune response in young infants, Med. Hypotheses 87 (2016) 90–96, http://dx.doi.org/10.1016/j.mehy.2015.11.012. A. Varvarigou, C.L. Bardin, K. Beharry, S. Chemtob, A. Papageorgiou, J.V. Aranda, Early ibuprofen administration to prevent patent ductus arteriosus in premature newborn infants, JAMA J. Am. Med. Assoc. 275 (1996) 539–544, http://dx.doi.org/10.1001/jama.275.7.539. D. Hirt, B. Van Overmeire, J.M. Treluyer, et al., An optimized ibuprofen dosing scheme for preterm neonates with patent ductus arteriosus, based on a population pharmacokinetic and pharmacodynamic study, Br. J. Clin. Pharmacol. 65 (2008) 629–636, http://dx.doi.org/10.1111/j.1365-2125.2008. 03118.x. S.P. Seslar, M.M. Garrison, C. Larison, J.C. Salerno, A multi-institutional analysis of inpatient treatment for supraventricular tachycardia in newborns and infants, Pediatr. Cardiol. 34 (2013) 408–414, http://dx.doi.org/10.1007/ s00246-012-0474-6. S.N. Weindling, J.P. Saul, E.P. Walsh, Efficacy and risks of medical therapy for supraventricular tachycardia in neonates and infants, Am. Heart J. 131 (1996) 66–72. M.C. Tavera, P.P. Bassareo, P. Neroni, et al., Supraventricular tachycardia in neonates: antiarrhythmic drug choice dilemma, J. Matern. Fetal Neonatal Med. 23 (Suppl. 3) (2010) 30–33, http://dx.doi.org/10.3109/14767058.2010. 517937. K.K. Wong, J.E. Potts, S.P. Etheridge, S. Sanatani, Medications used to manage supraventricular tachycardia in the infant—a North American survey, Pediatr. Cardiol. 27 (2006) 199–203, http://dx.doi.org/10.1007/s00246-005-1126-x. S. Sanatani, J.E. Potts, J.H. Reed, et al., The study of antiarrhythmic medications in infancy (SAMIS) a multicenter, randomized controlled trial comparing the efficacy and safety of digoxin versus propranolol for prophylaxis of supraventricular tachycardia in infants, Circ. Arrhythmia Elec. 5 (2012) 984–991, http://dx.doi.org/10.1161/Circep.112.972620. C.P. Hornik, P.Y. Chu, J.S. Li, R.H. Clark, P.B. Smith, K.D. Hill, Comparative effectiveness of digoxin and propranolol for supraventricular tachycardia in infants, Pediatr. Crit. Care Med. 15 (2014) 839–845, http://dx.doi.org/10.1097/ Pcc.0000000000000229. B.S. Moffett, P.J. Lupo, C.M. delaUz, et al., Efficacy of digoxin in comparison with propranolol for treatment of infant supraventricular tachycardia: analysis of a large, national database, Cardiol. Young 25 (2015) 1080–1085, http://dx.doi.org/10.1017/S10479511140 01619. A.L. Barton, B.S. Moffett, S.O. Valdes, C. Miyake, J.J. Kim, Efficacy and safety of high-dose propranolol for the management of infant supraventricular tachyarrhythmias, J. Pediatr. 166 (2015) 115–118, http://dx.doi.org/10.1016/j. jpeds.2014.08.067. M. Gheorghiade, K.F. Adams, W.S. Colucci, Digoxin in the management of cardiovascular disorders, Circulation 109 (2004) 2959–2964, http://dx.doi. org/10.1161/01.Cir.0000132482.95686.87. D.J. Goodman, R.M. Rossen, D.S. Cannom, A.K. Rider, D.C. Harrison, Effect of digoxin on atioventricular conduction: studies in patients with and without cardiac autonomic innervation, Circulation 51 (1975) 251–256. K.M. Ali, Collateral effects of antiarrhythmics in pediatric age, Curr. Pharm. Des. 14 (2008) 782–787. Y. Gong, Y. Chen, Q. Li, Z. Li, Population pharmacokinetic analysis of digoxin in Chinese neonates and infants, J. Pharmacol. Sci. 125 (2014) 142–149. M. Yukawa, E. Yukawa, F. Suematsu, et al., Population pharmacokinetic investigation of digoxin in Japanese infants and young children, J. Clin. Pharmacol. 51 (2011) 857–863, http://dx.doi.org/10.1177/ 0091270010374475. A. Smits, A. Kulo, J.N. de Hoon, K. Allegaert, Pharmacokinetics of drugs in neonates: pattern recognition beyond compound specific observations, Curr. Pharm. Des. 18 (2012) 3119–3146. D.E. Sweeney, V. Vallon, T. Rieg, W. Wu, T.F. Gallegos, S.K. Nigam, Functional maturation of drug transporters in the developing, neonatal, and postnatal kidney, Mol. Pharmacol. 80 (2011) 147–154, http://dx.doi.org/10.1124/mol. 110.070680. I. Ostman-Smith, Beta-blockers in pediatric hypertrophic cardiomyopathies, Rev. Recent Clin. Trials 9 (2014) 82–85. B.J. Maron, W.C. Roberts, S.E. Epstein, Sudden death in hypertrophic cardiomyopathy: a profile of 78 patients, Circulation 65 (1982) 1388–1394. D.G. Shand, C.G. Sell, J.A. Oates, Hypertrophic obstructive cardiomyopathy in an infant–propranolol therapy for three years, N. Engl. J. Med. 285 (1971) 843–844, http://dx.doi.org/10.1056/NEJ M197110072851507. I. Ostman-Smith, G. Wettrell, T. Riesenfeld, A cohort study of childhood hypertrophic cardiomyopathy: improved survival following high-dose beta-adrenoceptor antagonist treatment, J. Am. Coll. Cardiol. 34 (1999) 1813–1822. J.E. Brush Jr., G. Eisenhofer, M. Garty, et al., Cardiac norepinephrine kinetics in hypertrophic cardiomyopathy, Circulation 79 (1989) 836–844.

87

[63] I. Ostman-Smith, Reduction by oral propranolol treatment of left ventricular hypertrophy secondary to pressure-overload in the rat, Br. J. Pharmacol. 116 (1995) 2703–2709. [64] J.R. Skinner, A. Manzoor, A.M. Hayes, H.S. Joffe, R.P. Martin, A regional study of presentation and outcome of hypertrophic cardiomyopathy in infants, Heart 77 (1997) 229–233. [65] J.A. Decker, J.W. Rossano, E.O. Smith, et al., Risk factors and mode of death in isolated hypertrophic cardiomyopathy in children, J. Am. Coll. Cardiol. 54 (2009) 250–264, http://dx.doi.org/10.1016/j.jacc.2009.03.051. [66] C. Bourmayan, A. Razavi, C. Fournier, et al., Effect of propranolol on left ventricular relaxation in hypertrophic cardiomyopathy: an echographic study, Am. Heart J. 109 (1985) 1311–1316. [67] F. Gentile, R. Coppini, C. Ferrantini, et al., Life-Long treatment with late sodium current blocker reduces myocardial dysfunction and remodeling in a mouse model of hypertrophic cardiomyopathy, Biophys. J. 108 (2015) 291a, http://dx.doi.org/10.1016/j.bpj.2014.11.1588. [68] R. Coppini, C. Ferrantini, L. Yao, et al., Late sodium current inhibition reverses electromechanical dysfunction in human hypertrophic cardiomyopathy, Circulation 127 (2013) 575–584, http://dx.doi.org/10.1161/ CIRCULATIONAHA.112.134932. [69] R. Spoladore, M.S. Maron, R. D’Amato, P.G. Camici, I. Olivotto, Pharmacological treatment options for hypertrophic cardiomyopathy: high time for evidence, Eur. Heart J. 33 (2012) 1724–1733, http://dx.doi.org/10.1093/eurheartj/ ehs150. [70] I. Ostman-Smith, Hypertrophic cardiomyopathy in childhood and adolescence—strategies to prevent sudden death, Fundam. Clin. Pharmacol. 24 (2010) 637–652, http://dx.doi.org/10.1111/j.1472-8206.2010.00869.x. [71] S. Albers, B. Meibohm, T.S. Mir, S. Laer, Population pharmacokinetics and dose simulation of carvedilol in paediatric patients with congestive heart failure, Br. J. Clin. Pharmacol. 65 (2008) 511–522, http://dx.doi.org/10.1111/j.13652125.2007.03046.x. [72] J.E. Brush, G. Eisenhofer, M. Garty, et al., Cardiac norepinephrine kinetics in hypertrophic cardiomyopathy, Circulation 79 (1989) 836–844. [73] S.F. Zhou, Polymorphism of human cytochrome P450 2D6 and its clinical significance part I, Clin. Pharmacokinet. 48 (2009) 689–723. [74] L. Filippi, G. Cavallaro, P. Fiorini, et al., Propranolol concentrations after oral administration in term and preterm neonates, J. Matern. Fetal Neo. Med. 26 (2013) 833–840, http://dx.doi.org/10.3109/14767058.2012.755169. [75] M.A. Turner, U. Shah, Why are excipients important to neonates, Curr. Pharm. Des. 21 (2015) 5680–5687. [76] M.A. Turner, Neonatal drug development, Early Hum. Dev. 87 (2011) 763–768, http://dx.doi.org/10.1016/j.earlhumdev.2011.08.014. [77] M.W. Linakis, J.K. Roberts, A.C. Lala, et al., Challenges associated with route of administration in neonatal drug delivery, Clin. Pharmacokinet. 55 (2016) 185–196, http://dx.doi.org/10.1007/s40262-015-0313-z. [78] K. Allegaert, B.J. Anderson, V. Cossey, N.H.G. Holford, Limited predictability of amikacin clearance in extreme premature neonates at birth, Br. J. Clin. Pharmacol. 61 (2006) 39–48, http://dx.doi.org/10.1111/j.1365-2125.2005. 02530.x. [79] A. Campino, E. Santesteban, P. Pascual, et al., Strategies implementation to reduce medicine preparation error rate in neonatal intensive care units, Eur. J. Pediatr. (2015), http://dx.doi.org/10.1007/s00431-015-2679-1. [80] G. Nellis, T. Metsvaht, H. Varendi, et al., Potentially harmful excipients in neonatal medicines: a pan-European observational study, Arch. Dis. Child. 100 (2015) 694–699, http://dx.doi.org/10.1136/archdischild-2014-307793. [81] V. Klingmann, A. Seitz, T. Meissner, J. Breitkreutz, A. Moeltner, H.M. Bosse, Acceptability of uncoated mini-tablets in Neonates—a randomized controlled trial, J. Pediatr. 167 (2015) 893–896e2, http://dx.doi.org/10.1016/j.jpeds.2015. 07.010. [82] K. Allegaert, S. Vanhaesebrouck, A. Kulo, et al., Prospective assessment of short-term propylene glycol tolerance in neonates, Arch. Dis. Child. 95 (2010) 1054–1058, http://dx.doi.org/10.1136/adc.2010.190330. [83] R.F. De Cock, C.A. Knibbe, A. Kulo, et al., Developmental pharmacokinetics of propylene glycol in preterm and term neonates, Br. J. Clin. Pharmacol. 75 (2013) 162–171, http://dx.doi.org/10.1111/j.1365-2125.2012.04312.x. [84] H. Mulla, S. Yakkundi, J. McElnay, et al., An observational study of blood concentrations and kinetics of methyl- and propyl-parabens in neonates, Pharm. Res. 32 (2015) 1084–1093, http://dx.doi.org/10.1007/s11095-0141520-2. [85] J.M. Davis, M.A. Turner, Global collaboration to develop new and existing drugs for neonates, JAMA Pediatr. 169 (2015) 887–888, http://dx.doi.org/10. 1001/jamapediatrics.2015.1640. [86] R.M. Ward, C.M. Sherwin, Ethics of drug studies in the newborn, Paediatr. Drugs 17 (2015) 37–42, http://dx.doi.org/10.1007/s40272-014-0099-8.