Developmental changes in the liver weight- and body weight-normalized clearance of theophylline, phenytoin and cyclosporine in children

Severe hypoglycemia in propranolol treatment for infantile hemangiomas

BACKGROUND

Infantile hemangioma (IH), formerly termed strawberry hemangioma, is a benign vascular tumor caused by capillary endothelial cell proliferation. The tumor regresses after 1 year of age, but sequelae occur in approximately half of the patients without systemic treatment. Propranolol (PPL) is currently the first-line therapeutic agent in Japan as well as in Western countries. It is not commonly known that PPL may induce severe hypoglycemia, in addition to cardiovascular and respiratory side effects.

METHODS

We retrospectively analyzed patients with severe PPL-induced hypoglycemia in the 3 years since the launch of Hemangiol®, a PPL preparation specific for IH, in Japan in 2016.

RESULTS

The incidence of severe hypoglycemia and of hypoglycemic convulsions following PPL treatment was estimated to be 0.54% and 0.35%, respectively. The incidence of hypoglycemic convulsions appeared to be higher in Japan than in Western countries. Severe hypoglycemia was common in infants aged >1 year, when PPL was used for ≥6 months. Severe hypoglycemia often develops from 05:00 a.m. to 09:00 a.m. and is frequently associated with prolonged periods of fasting, poor feeding, or poor physical conditions.

CONCLUSION

To avoid the risk of hypoglycemia, the treatment should be initiated by 6 months of age during the proliferative phase at the latest, and should not be extended indiscriminately beyond 1 year of age. Guardians should be advised not to administer PPL on an empty stomach, in the presence of poor feeding, or who are in poor physical condition, not to prolong fasting after PPL administration, and to monitor the child's condition immediately after he or she wakes up.

Are body surface area based estimates of liver volume applicable to children with overweight or obesity? An in vivo validation study

The liver is the primary organ responsible for clearing most drugs from the body and thus determines systemic drug concentrations over time. Drug clearance by the liver appears to be directly related to organ size. In children, organ size changes as children age and grow. Liver volume has been correlated with body surface area (BSA) in healthy children and adults and has been estimated by functions of BSA. However, these relationships were derived from "typical" populations and it is unknown whether they extend to estimations of liver volumes for population "outliers," such as children with overweight or obesity, who today represent one-third of the pediatric population. Using computerized tomography or magnetic resonance imaging, this study measured liver volumes in 99 children (2-21 years) with normal weight, overweight, or obesity and compared organ measurements with estimates calculated using an established liver volume equation. A previously developed equation relating BSA to liver volume adequately estimates liver volumes in children, regardless of weight status.

A Clinical Decision Support Tool to Find the Best Initial Intravenous Cyclosporine Regimen in Pediatric Hematopoietic Stem Cell Transplantation

To optimize cyclosporine A (CsA) dosing regimen in pediatric patients undergoing hematopoietic stem cell transplantation (HSCT), we aimed to provide clinicians with a validated decision support tool for determining the most suitable first dose of intravenous CsA. We used a 10-year monocentric data set of pediatric patients undergoing HSCT. Discretization of all variables was performed according to literature or thanks to algorithms using Shannon entropy (from information theory) or equal width intervals. The first 8 years were used to build the Bayesian network model. This model underwent a 10-fold cross-validation, and then a prospective validation with data of the last 2 years. There were 3.3% and 4.1% of missing values in the training and the validation data set, respectively. After prospective validation, the Tree-Augmented Naïve Bayesian network shows interesting prediction performances with an average area under the receiver operating characteristic curve of 0.804, 32.8% of misclassified patients, a true-positive rate of 0.672, and a false-positive rate of 0.285. This validated model allows good predictions to propose an optimized and personalized initial CsA dose for pediatric patients undergoing HSCT. The clinical impact of its use should be further evaluated.

Immune cell function assays in the diagnosis of infection in pediatric liver transplantation: an open-labeled, two center prospective cohort study

BACKGROUND

Limited studies have been performed in assessment of immune status of pediatric liver transplants (PLTs). We conducted this study to evaluate Cylex immune cell function assay in diagnosis of infection and its potential clinical application in Chinese infant PLTs.

METHODS

In this prospective cohort study, 227 infant PLTs from two medical centers were enrolled, and 216 completed the study. Cylex ATP values were measured before and after liver transplantation (LT) at week 1, 2, 3, 4, 8, 12 and 24 respectively. Accordingly, patients' clinical records, including demographic data, liver function results, tacrolimus dosages and concentrations were collected and analyzed.

RESULTS

One hundred and sixty of 216 PLTs (74.1%) were diagnosed infection based on the parameters including abnormal vital signs, imaging changes, and pathogens detection, while 44 (20.4%) were clinically stable and 12 (5.6%) experienced acute rejection. The median Cylex ATP value in infant PLTs post-surgery reduced significantly in infection group compared to stable group (median, 137 vs. 269 ng/mL, P<0.001). Receiver operating characteristic (ROC) curve analysis determined that the cut-off value of Cylex ATP was 152 ng/mL in diagnosis of infection [area under the curve (AUC): 0.784, 95% CI: 0.720-0.848]. Meanwhile, Cylex ATP value showed no correlation to tacrolimus dosage, blood concentration, dose-normalized concentration/dose ratio or Kaup index. However, it tended to correlate weakly with the white blood cell (WBC) number (R =0.462, P<0.0001) and lymphocyte counts (R =0.363, P<0.0001).

CONCLUSIONS

In this study, we demonstrated that low Cylex ATP represented partly over-immunosuppression and had diagnostic value in infant PLTs with infections, which might assist individualized immunosuppression in PLT patients.

A decision support tool to find the best cyclosporine dose when switching from intravenous to oral route in pediatric stem cell transplant patients

PURPOSE

Managing the pharmacokinetic variability of immunosuppressive drugs after pediatric hematopoietic stem cell transplantation (HSCT) is a clinical challenge. Thus, the aim of our study was to design and validate a decision support tool predicting the best first cyclosporine oral dose to give when switching from intravenous route.

METHODS

We used 10-years pediatric HSCT patients' dataset from 2008 to 2018. A tree-augmented naïve Bayesian network model (method belonging to artificial intelligence) was built with data from the first eight-years, and validated with data from the last two.

RESULTS

The Bayesian network model obtained showed good prediction performances, both after a 10-fold cross-validation and external validation, with respectively an AUC-ROC of 0.89 and 0.86, a percentage of misclassified patients of 28.7% and 35.2%, a true positive rate of 0.71 and 0.65, and a false positive rate of 0.12 and 0.14 respectively.

CONCLUSION

The final model allows the prediction of the most likely cyclosporine oral dose to reach the therapeutic target specified by the clinician. The clinical impact of using this model needs to be prospectively warranted. Respecting the decision support tool terms of use is necessary as well as remaining critical about the prediction by confronting it with the clinical context.

Investigating the Role of Altered Systemic Albumin Concentration on the Disposition of Theophylline in Adult and Pediatric Patients with Asthma by Using the Physiologically Based Pharmacokinetic Approach

Theophylline is commonly used for the treatment of asthma and has a low hepatic clearance. The changes in plasma albumin concentration occurring in asthma may affect the exposure of theophylline. The aim of the presented work was to predict theophylline pharmacokinetics (PK) after incorporating the changes in plasma albumin concentration occurring in patients with asthma into a physiologically based pharmacokinetic (PBPK) model to see whether these changes can affect the systemic theophylline concentrations in asthma. The PBPK model was developed following a systematic model building approach using Simcyp. The predictions were performed initially in healthy adults after intravenous and oral drug administration. Only when the developed adult PBPK model had adequately predicted theophylline PK in healthy adults, the changes in plasma albumin concentrations were incorporated into the model for predicting drug exposure in patients with asthma. After evaluation of the developed model in the adult population, it was scaled to children on physiologic basis. The model evaluation was performed by using visual predictive checks and comparison of ratio of observed and predicted (R_obs/Pre) PK parameters along with their 2-fold error range. The developed PBPK model has effectively described theophylline PK in both healthy and diseased populations, as R_obs/Pre for all the PK parameters were within the 2-fold error limit. The predictions in patients with asthma showed that there were no significant changes in PK parameters after incorporating the changes in serum albumin concentration. The mechanistic nature of the developed asthma-PBPK model can facilitate its extension to other drugs. SIGNIFICANCE STATEMENT: Exposure of a low hepatic clearance drug like theophylline may be susceptible to plasma albumin concentration changes that occur in asthma. These changes in systemic albumin concentrations can be incorporated into a physiologically based pharmacokinetic model to predict theophylline pharmacokinetics in adult and pediatric asthma populations. The presented work is focused on predicting theophylline absorption, distribution, metabolism, and elimination in adult and pediatric asthma populations after incorporating reported changes in serum albumin concentrations to see their impact on the systemic theophylline concentrations.

Phase I/IIa Trial of Atorvastatin in Patients with Acute Kawasaki Disease with Coronary Artery Aneurysm

OBJECTIVES

To determine the safety, tolerability, pharmacokinetics, and immunomodulatory effects of a 6-week course of atorvastatin in patients with acute Kawasaki disease with coronary artery (CA) aneurysm (CAA).

STUDY DESIGN

This was a Phase I/IIa 2-center dose-escalation study of atorvastatin (0.125-0.75 mg/kg/day) in 34 patients with Kawasaki disease (aged 2-17 years) with echocardiographic evidence of CAA. We measured levels of the brain metabolite 24(S)-hydroxycholesterol (24-OHC), serum lipids, acute-phase reactants, liver enzymes, and creatine phosphokinase; peripheral blood mononuclear cell populations; and CA internal diameter normalized for body surface area before atorvastatin treatment and at 2 and 6 weeks after initiation of atorvastatin treatment.

RESULTS

A 6-week course of up to 0.75 mg/kg/day of atorvastatin was well tolerated by the 34 subjects (median age, 5.3 years; IQR, 2.6-6.4 years), with no serious adverse events attributable to the study drug. The areas under the curve for atorvastatin and its metabolite were larger in the study subjects compared with those reported in adults, suggesting a slower rate of metabolism in children. The 24-OHC levels were similar between the atorvastatin-treated subjects and matched controls.

CONCLUSIONS

Atorvastatin was safe and well tolerated in our cohort of children with acute Kawasaki disease and CAA. A Phase III efficacy trial is warranted in this patient population, which may benefit from the known anti-inflammatory and immunomodulatory effects of this drug.

Scoring criteria for determining the safety of liver resection for malignant liver tumors

BACKGROUND

Liver resection has become safer as it has become less invasive. However, the minimum residual liver volume (RLV) required to maintain homeostasis is unclear. Furthermore, the formulae used to calculate standard liver volume (SLV) are complex.

AIM

To review previously reported SLV formulae and the methods used to evaluate the minimum RLV, and explore the association between liver volume and mortality.

METHODS

A systematic review of Medline, PubMed, and grey literature was performed. References in the retrieved articles were cross-checked manually to obtain further studies. The last search was conducted on January 20, 2019. We developed an SLV formula using data for 86 consecutive patients who underwent hepatectomy at our institution between July 2009 and August 2011.

RESULTS

Linear regression analysis revealed the following formula: SLV (mL) = 822.7 × body surface area (BSA) − 183.2 (R² = 0.419 and R = 0.644, P < 0.001). We retrieved 25 studies relating to SLV formulae and 12 studies about the RLV required for safe liver resection. Although the previously reported formulae included various coefficient and constant values, a simplified version of the SLV, the common SLV (cSLV), can be calculated as follows: cSLV (mL) = 710 or 770 × BSA. The minimum RLV for normal and damaged livers ranged from 20%-40% and 30%-50%, respectively. The Sapporo score indicated that the minimum RLV ranges from 35%-95% depending on liver function.

CONCLUSION

We reviewed SLV formulae and the minimum RLV required for safe liver resection. The Sapporo score is the only liver function-based method for determining the minimum RLV.

Bayesian Networks: A New Approach to Predict Therapeutic Range Achievement of Initial Cyclosporine Blood Concentration After Pediatric Hematopoietic Stem Cell Transplantation

BACKGROUND

Pediatric hematopoietic stem cell transplantation (HSCT) allows the treatment of numerous diseases, both malignant and non-malignant. Cyclosporine, a narrow therapeutic index drug, is the major immunosuppressant used to prevent graft-versus-host disease (GVHD), but may also cause severe adverse effects in case of overdosing.

OBJECTIVE

The objective of this study is to predict the initial cyclosporine residual blood concentration value after pediatric HSCT, and consequently the dose necessary to reach the therapeutic range, using a mathematical individual predictive model.

METHODS

Clinical and biological data collected from the graft infusion for 2 months after transplantation in 155 pediatric patients undergoing HSCT between 2008 and 2016 were used to generate synthetic data for 1000 subjects which were used to build a Bayesian network model. We compared the characteristics and sensitivity to clinical or biological missing data of this model with four other methods.

RESULTS

The tree-augmented Naïve Bayesian network showed the best characteristics, with no missing data (area under the curve of the receiving operator characteristics curve [AUC-ROC] of 0.89 ± 0.02), 18.9 ± 2.6% of patients misclassified, and positive and negative predictive values of 85.9 ± 3.4% and 74.2 ± 5.1%, respectively, and this trend is found in the synthetic dataset from no to 10% missing data. The most relevant variables that could influence whether the initial residual cyclosporine concentration is in the therapeutic range are the last dose before measurement and the mean dose before measurement.

CONCLUSIONS

We developed and cross-validated an online Bayesian network to predict the first cyclosporine concentration after pediatric HSCT. This model allows simulation of different dosing regimens, and enables the best dosing regimen to reach the therapeutic range immediately after transplantation to be found, minimizing the risk of adverse effects and GVHD occurrence.

Cytochrome P450 and flavin-containing monooxygenase families: age-dependent differences in expression and functional activity

BackgroundAge-dependent differences in pharmacokinetics exist for metabolically cleared medications. Differential contributions in the cytochrome P450 3A (CYP3A), CYP2C, and flavin-containing monooxygenases (FMOs) families have an important role in the metabolic clearance of a large number of drugs administered to children.MethodsUnlike previous semiquantitative characterization of age-dependent changes in the expression of genes and proteins (western blot analysis), this study quantifies both gene and absolute protein expression in the same fetal, pediatric, and adult hepatic tissue. Expression was then correlated with the corresponding functional activities in the same samples.ResultsCYP3A and FMO families showed a distinct switch from fetal (CYP3A7 and FMO1) to adult isoforms (CYP3A4 and FMO3) at birth, whereas CYP2C9 showed a linear maturation from birth into adulthood. In contrast, analysis of CYP2C19 revealed higher expression and catalytic efficiency in pediatric samples compared with that in fetal and adult samples. Further, CYP3A and FMO enzymes exhibited an unexpectedly higher functional activity in fetal samples not entirely explained by protein expression.ConclusionThese surprising findings suggest that CYP and FMO enzymes may encounter development-related differences in their microenvironments that can influence the enzyme activity in addition to protein expression levels.

Dosing anticancer drugs in infants: Current approach and recommendations from the Children's Oncology Group's Chemotherapy Standardization Task Force

An analysis of dose modifications for infants in 29 Children's Oncology Group protocols across 10 cancer types revealed 11 sets of criteria defining the infant population using age, weight, body surface area (BSA), or a combination of these parameters and eight dose modification methods. A new method of dosing anticancer drugs in infants was developed based on the rationale that prior modifications were implemented to reduce toxicity, which is not cancer-specific. The new method uses BSA dose banding in dosing tables for infants and children with a BSA <0.6 m² and gradually transitions from body weight based to BSA-based dosing.

Tacrolimus dose requirements in paediatric renal allograft recipients are characterized by a biphasic course determined by age and bone maturation

AIMS

Despite longstanding recognition of significant age-dependent differences in drug disposition during childhood, the exact course and the underlying mechanisms are not known. Our aim was to determine the course and determinants of individual relative dose requirements, during long-term follow-up in children on tacrolimus.

METHODS

This was a cohort study in a tertiary hospital with standardized annual pharmacokinetic (PK) follow-up (AUC_0-12hr ) in recipients of a renal allograft (≤19 years), between 1998 and 2015. In addition, the presence of relevant pharmacogenetic variants was determined. The evolution of dose-corrected exposure was evaluated using mixed models.

RESULTS

A total of 184 PK visits by 43 children were included in the study (median age: 14.6). AUC_0-12h corrected for dose per kg demonstrated a biphasic course: annual increase 4.4% (CI: 0.3-8.7%) until ±14 years of age, followed by 13.4% increase (CI 8.7-18.3%). Moreover, exposure corrected for dose per m² proved stable until 14 years (+0.8% annually; CI: -3.0 to +4.8%), followed by a steep increase ≥14 years (+11%; CI: 7.0-16.0%). Analysis according to bone maturation instead of age demonstrated a similar course with a distinct divergence at TW2: 800 (P = 0.01). Genetic variation in CYP3A4, CYP3A5, and CYP3A7 was associated with altered dose requirements, independent of age.

CONCLUSIONS

Children exhibit a biphasic course in tacrolimus disposition characterized by a high and stable drug clearance until a specific phase in pubertal development (TW2: 800 at age: ±14 years), followed by an important decline in relative dose requirements thereafter. Pharmacogenetic variation demonstrated an age/puberty independent effect. We suggest a critical reappraisal of current paediatric dosing algorithms for tacrolimus and drugs with a similar disposition.

Development of a Pediatric Physiologically Based Pharmacokinetic Model for Sirolimus: Applying Principles of Growth and Maturation in Neonates and Infants

This study describes the maturation of sirolimus clearance in a cohort of very young pediatric patients with vascular anomalies. The relationship between allometrically scaled in vivo clearance and age was described by the E_max model in patients aged 1 month to 2 years. Consistent with the observed increase, in vitro intrinsic clearance of sirolimus using pediatric liver microsomes showed a similar age-dependent increase. In children older than 2 years, allometrically scaled sirolimus clearance did not show further maturation. Simulated clearance estimates with a sirolimus physiologically based pharmacokinetic model that included CYP3A4/5/7 and CYP2C8 maturation profiles were in close agreement with observed in vivo clearance values. In addition, physiologically based pharmacokinetic model-simulated sirolimus pharmacokinetic profiles predicted the actual observations well. These results demonstrate the utility of a physiologically based pharmacokinetic modeling approach for the prediction of the developmental trajectory of sirolimus metabolic activity and its effects on total body clearance in neonates and infants.

The relation between dosage, serum concentrations, and clinical outcome in children and adolescents treated with sertraline: a naturalistic study

OBJECTIVE

This naturalistic therapeutic drug monitoring (TDM) study aimed to evaluate the relationship between dosage, serum concentration, and clinical outcome in children and adolescents treated with the serotonin reuptake inhibitor sertraline for different indications.

METHODS

Steady-state trough serum concentrations were analyzed in 90 subjects, treated with 25-200 mg sertraline per day. Therapeutic efficacy was assessed by the Clinical Global Impression Improvement subscale and side effects by the Udvalg for Kliniske Undersogelser-Side Effect Rating Scale.

RESULTS

In the study population, children were administered higher body weight normalized daily doses than adolescents. The relationships between sertraline daily dosage and serum concentrations (rs = 0.67, P < 0.0001) as well as between body weight normalized daily doses and serum concentrations (r = 0.62, P < 0.0001) were linear. In the whole patient group, no correlation between serum concentrations and either the therapeutic effect or side effects could be observed, neither significant effects of gender, age, concomitant medications, or smoking habits. When analyzing just the patients with depression, those with side effects had significantly higher sertraline serum concentrations than those without (44.8 ng/mL versus 22.3 ng/mL, P = 0.01). In general, occurrence of side effects was significantly more frequent in patients with psychiatric comedication (37.9%) than those without (11.5%, P = 0.002).

DISCUSSION

As this study has the typical limitations of naturalistic studies, the results should be interpreted cautiously. From the data, it is not possible to suggest an age-specific therapeutic window for children and adolescents. However, as the intraindividual variability of sertraline serum concentrations is known to be low, TDM may certainly help to predict serum concentrations after dose adjustment, to assess pharmacokinetic drug-drug interactions influencing serum concentrations and the patient's compliance, finally allowing for personalizing dose through TDM.

From gut to kidney: transporting and metabolizing calcineurin-inhibitors in solid organ transplantation

Since their introduction circa 35 years ago, calcineurin-inhibitors (CNI) have become the cornerstone of immunosuppressive therapy in solid organ transplantation. However, CNI's possess a narrow therapeutic index with potential severe consequences of drug under- or overexposure. This demands a meticulous policy of Therapeutic Drug Monitoring (TDM) to optimize outcome. In clinical practice optimal dosing is difficult to achieve due to important inter- and intraindividual variation in CNI pharmacokinetics. A complex and often interdependent set of factors appears relevant in determining drug exposure. These include recipient characteristics such as age, race, body composition, organ function, and food intake, but also graft-related characteristics such as: size, donor-age, and time after transplantation can be important. Fundamental (in vitro) and clinical studies have pointed out the intrinsic relation between the aforementioned variables and the functional capacity of enzymes and transporters involved in CNI metabolism, primarily located in intestine, liver and kidney. Commonly occurring polymorphisms in genes responsible for CNI metabolism (CYP3A4, CYP3A5, CYP3A7, PXR, POR, ABCB1 (P-gp) and possibly UGT) are able to explain an important part of interindividual variability. In particular, a highly prevalent SNP in CYP3A5 has proven to be an important determinant of CNI dose requirements and drug-dose-interactions. In addition, a discrepancy in genotype between graft and receptor has to be taken into account. Furthermore, common phenomena in solid organ transplantation such as inflammation, ischemia- reperfusion injury, graft function, co-medication, altered food intake and intestinal motility can have a differential effect on the expression enzymes and transporters involved in CNI metabolism. Notwithstanding the built-up knowledge, predicting individual CNI pharmacokinetics and dose requirements on the basis of current clinical and experimental data remains a challenge.

Body weight-dependent pharmacokinetics of busulfan in paediatric haematopoietic stem cell transplantation patients: towards individualized dosing

BACKGROUND AND OBJECTIVES

The wide variability in pharmacokinetics of busulfan in children is one factor influencing outcomes such as toxicity and event-free survival. A meta-analysis was conducted to describe the pharmacokinetics of busulfan in patients from 0.1 to 26 years of age, elucidate patient characteristics that explain the variability in exposure between patients and optimize dosing accordingly.

PATIENTS AND METHODS

Data were collected from 245 consecutive patients (from 3 to 100 kg) who underwent haematopoietic stem cell transplantation (HSCT) in four participating centres. The inter-patient, inter-occasion and residual variability in the pharmacokinetics of busulfan were estimated with a population analysis using the nonlinear mixed-effects modelling software NONMEM VI. Covariates were selected on the basis of their known or theoretical relationships with busulfan pharmacokinetics and were plotted independently against the individual pharmacokinetic parameters and the weighted residuals of the model without covariates to visualize relations. Potential covariates were formally tested in the model.

RESULTS

In a two-compartment model, body weight was the most predictive covariate for clearance, volume of distribution and inter-compartmental clearance and explained 65%, 75% and 40% of the observed variability, respectively. The relationship between body weight and clearance was characterized best using an allometric equation with a scaling exponent that changed with body weight from 1.2 in neonates to 0.55 in young adults. This implies that an increase in body weight in neonates results in a larger increase in busulfan clearance than an increase in body weight in older children or adults. Clearance on the first day was 12% higher than that of subsequent days (p < 0.001). Inter-occasion variability on clearance was 15% between the 4 days. Based on the final pharmacokinetic-model, an individualized dosing nomogram was developed.

CONCLUSIONS

The model-based individual dosing nomogram is expected to result in predictive busulfan exposures in patients ranging between 3 and 65 kg and thereby to a safer and more effective conditioning regimen for HSCT in children.

The effects of a high-fat and high-energy diet on the hepatic expression of CYP3A in developing female rats

We aimed to investigate the effects of high-fat and high-energy (HFHE) diets on the hepatic expression of cytochrome P-450 3A (CYP3A) in developing female rats. The pups of the dams fed with the standard diet were defined as the NN group and those fed the HFHE diet were defined as the NH group. The mRNA and protein expression, the protein localization and activity was determined. The mRNA expression of CYP3A1 on day 3 in the NH group were higher versus NN groups (p < 0.05) and the expression of the NH group on days 28 and 56 were lower versus the NN group (p < 0.01). CYP3A1 immunolabeling had a zonal-restricted expressions pattern on day 28 and after in the NN groups, while the obvious zonal expression pattern was observed in the NH group on day 84. The mean activity for the NH groups on days 3, 7, 14 and 28 was higher versus the NN groups (p < 0.05). On day 84, the activity was lower for the NH group versus the NN group (p < 0.05). Our findings provide a basis for further studies on appropriate medication regimen in obese children.

Prediction of drug clearance in children 3 months and younger: an allometric approach

BACKGROUND

Sometimes it might not be possible to conduct a pharmacokinetic (PK) study in neonates and infants. Under these circumstances, one would like to predict PK parameters in this age group. Because drug clearance is the most important PK parameter, the objective of this study was to describe an allometric method to predict drug clearance in children ≤3 months.

METHODS

In total, 43 drugs (107 observations) were randomly selected for this study. The age of the children ranged from 0 to 1 year. Children were divided into two groups: ≤3 months and ≥3 months to 1 year. Drug clearance (CL) in children was predicted using the following equation: CL in the child=adult CL×(weight of the child/70)(0.75 or 1.0 or 1.2).

RESULTS

The results of the study indicated that the exponent 1.2 performs better in the prediction of drug clearance than exponent 1.0 or 0.75 for children ≤3 months. By contrast, exponent 1.0 provided better prediction for children ≥3 months to 1 year than exponent 1.2. Exponent 0.75 provided the worst results leading to substantial prediction error in children 0-1 year (in many instances more than 1000% prediction error).

CONCLUSIONS

Overall, it appears that exponent 1.2 is the best method out of three methods for reasonably accurate prediction of drug clearance in children ≤3 months old. However, exponent 1.2 will underpredict drug clearance in children older than 3 months. The suggested approach could be used to support the choice of the initial dose in clinical trials for children ≤3 months old.

Adverse drug reactions in newborns, infants and toddlers: pediatric pharmacovigilance between present and future

INTRODUCTION

The detection, assessment, understanding and prevention of adverse drug reactions (ADRs) are the primary aims of pharmacovigilance activities. Pediatric patients, especially all newborns and infants, are particularly at risk for experiencing drug-related adverse events.

AREAS COVERED

This review briefly analyzes the physiological peculiarities of pharmacodynamic and pharmacokinetic aspects of drugs in newborns, infants and toddlers and children. It also deals with specific pediatric pharmacovigilance aspects, such as the frequent use of unlicensed and/or off-label drugs in neonatal intensive care units in European countries and in Australia. This review reports on European, American and Canadian data about the incidence and type of pediatric ADRs, particularly focusing on neonates, infants and toddlers.

EXPERT OPINION

The awareness of pediatricians about the importance of reporting ADRs should be stimulated, new reporting systems should be encouraged and pediatric pharmacovigilance activities should be improved, first, by intensifying active post-marketing surveillance methods.

Hepatotoxicity and gene expression down-regulation of CYP isozymes caused by renal ischemia/reperfusion in the rat

Renal ischemia/reperfusion (I/R) occurs in many clinical scenarios, including trauma, elective surgery, and transplantation. Events initiated by this process can lead to inflammation in the kidneys, culminating in local injury as well as distant organ dysfunction. The objectives of this study were to investigate the changes in the functions of the liver and the regulation of gene expression of cytochrome P450 (CYP) isozymes after renal I/R. Hepatoxocity was assessed by serum alanine aminotransferase (sALT), serum aspartate aminotransferase (sAST) and liver glutathione-S-transferase (GST) activities, liver glutathione (GSH) level, and histopathological examination. Hepatic cytochrome P4503A1 (CYP3A1) and cytochrome P4502E1 (CYP2E1) activities were measured by erythromycin N-demethylase (ERD) and aniline hydroxylase (ANH) activities, respectively. CYP3A1 and CYP2E1 mRNA expression was determined by RT-PCR. Results showed that activities of sALT and sAST were significantly increased, while hepatic CYP3A1and CYP2E1 activities as well as their respective mRNA levels were significantly decreased after renal I/R. Moreover, hepatic tissue congestion, degeneration, and local necrosis were observed in rats after 1, 4, and 8h renal reperfusion following 2h renal ischemia. In conclusion, the present study suggests that renal I/R can cause hepatotoxicity and gene expression down-regulation of CYP isozymes in rats.

Mechanism-based concepts of size and maturity in pharmacokinetics

Growth and development can be investigated using readily observable demographic factors such as weight and age. Size is the primary covariate and can be referenced to a 70-kg person with allometry using a coefficient of 0.75 for clearance and 1 for volume. The use of these coefficients is supported by fractal geometric concepts and observations from diverse areas in biology. Fat free mass (FFM) might be expected to do better than total body weight when there are wide variations in fat affecting body composition. Clearance pathways develop in the fetus before birth. The use of postnatal age as a descriptor of maturation is unsatisfactory because birth may occur prematurely; therefore postmenstrual age is a superior predictor of elimination function. A sigmoid E(max) model (Hill equation) describes gradual maturation of clearance in early life leading to a mature adult clearance achieved at a later age.

Prediction of Drug Clearance in Children: Impact of Allometric Exponents, Body Weight, and Age

In recent years, with the advent of pediatric exclusivity and requirements for conducting clinical studies involving children, emphasis has been placed on finding safe and efficacious doses of drugs for children. It has been suggested that one can predict the clearance (CL) of a drug in children according to this equation: CL in the child = Adult CL * (Weight of the child/70)0.75. In light of the controversy surrounding the exponent of 0.75 for the prediction of clearance, the objectives of the study were as follows: (1) to develop allometric equations based on body weight or age to predict clearance of a drug in children; (2) to determine if the fixed exponent of 0.75 is a suitable exponent for the prediction of clearance in children from adult data, as compared with the allometric exponent generated for individual drugs; (3) to determine if the allometric equation generated on the basis of age predicts clearance in children better or worse than the allometric equation generated on the basis of body weight; and (4) to propose a new approach based on the findings of the current evaluation. Five methods were used to predict drug clearance in children. Six drugs were used in the evaluation, and drug clearance in each child was predicted for a given drug. Besides evaluating the exponent of 0.75, allometric equations were developed using double log plots of clearance versus body weight or age. The exponents of the allometric equations were then used to predict drug clearance by replacement of 0.75 in the aforementioned equation. The results of the study indicate that 0.75 is not the best exponent for prediction of drug clearance in children, and a more suitable approach is to develop an allometric relationship for a given drug in children. For all 6 drugs, there were 77 children in whom the clearance was predicted. There were 48 observations for which error in the predicted clearance was 50% or more with use of the exponent 0.75, whereas there were only 13 observations with prediction error > or = 50% when 0.75 was replaced by an allometric exponent developed for a given drug. In order to predict drug clearance in children with reasonable accuracy, an allometric equation should be developed for every drug and the exponent 0.75 should be replaced by the exponent of the allometric equation developed for that drug.

Guidelines on paediatric dosing on the basis of developmental physiology and pharmacokinetic considerations

The approach to paediatric drug dosing needs to be based on the physiological characteristics of the child and the pharmacokinetic parameters of the drug. This review summarises the current knowledge on developmental changes in absorption, distribution, metabolism and excretion and combines this knowledge with in vivo and in vitro pharmacokinetic data that are currently available. In addition, dosage adjustments based on practical problems, such as child-friendly formulations and feeding regimens, disease state, genetic make-up and environmental influences are presented. Modification of a dosage based on absorption, depends on the route of absorption, the physico chemical properties of the drug and the age of the child. For oral drug absorption, a distinction should be made between the very young and children over a few weeks old. In the latter case, it is likely that practical considerations, like appropriate formulations, have much greater relevance to oral drug absorption. The volume of distribution (V(d)) may be altered in children. Hydrophilic drugs with a high V(d) in adults should be normalised to bodyweight in young children (age <2 years), whereas hydrophilic drugs with a low V(d) in adults should be normalised to body surface area (BSA) in these children. For drugs that are metabolised by the liver, the effect of the V(d) becomes apparent in children <2 months of age. In general, only the first dose should be based on the V(d); subsequent doses should be determined by the clearance. Pharmacokinetic studies on renal and liver function clarify that a distinction should be made between maturation and growth of the organs. After the maturation process has finished, the main influences on the clearance of drugs are growth and changes in blood flow of the liver and kidney. Drugs that are primarily metabolised by the liver should be administered with extreme care until the age of 2 months. Modification of dosing should be based on response and on therapeutic drug monitoring. At the age of 2-6 months, a general guideline based on bodyweight may be used. After 6 months of age, BSA is a good marker as a basis for drug dosing. However, even at this age, drugs that are primarily metabolised by cytochrome P450 2D6 and uridine diphosphate glucuronosyltransferase should be normalised to bodyweight. In the first 2 years of life, the renal excretion rate should be determined by markers of renal function, such as serum creatinine and p-aminohippuric acid clearance. A dosage guideline for drugs that are significantly excreted by the kidney should be based on the determination of renal function in first 2 years of life. After maturation, the dose should be normalised to BSA. These guidelines are intended to be used in clinical practice and to form a basis for more research. The integration of these guidelines, and combining them with pharmacodynamic effects, should be considered and could form a basis for further study.

Prediction of drug clearance in children from adults: a comparison of several allometric methods

AIMS

In recent years with the advent of paediatric exclusivity and requirements to conduct clinical studies in children, the current emphasis is to find a safe and efficacious dose of a drug in children. It has been suggested that one can predict the clearance of a drug in children according to the equation: CL in the child=adult CLx(weight of the child/70)0.75. Considering the controversy surrounding the exponent of 0.75 for the prediction of clearance and lack of any systematic evaluation of the aforementioned proposal, the objectives of the study were as follows: (i) to determine if indeed the exponent 0.75 is the most suitable exponent for the prediction of clearance in children from adult data; (ii) to explore and search for other exponents that are more accurate or as good as 0.75; and (iii) to propose a new approach (if any) based on the findings of the current evaluation.

METHODS

Six methods were used to predict clearance of drugs in children from adult data. Besides evaluating the exponent of 0.75, exponents of 0.80, 0.85 and 1.0 were also evaluated. An empirical approach based on kidney and liver weights was also examined. Based on the results of five methods, a sixth method was introduced.

RESULTS

The results of the study indicate that no single method is suitable for all drugs or for all age groups. The exponents 0.75, 0.80, and 0.85 provided the same degree of accuracy or error in the prediction of clearance in children.

CONCLUSIONS

Since no single method is suitable for all drugs or for all age groups. A combination of approaches is suggested which may help in improving the prediction of clearance in children from adult data.

Soy protein isolate induces CYP3A1 and CYP3A2 in prepubertal rats

Feeding soy diets has been shown to induce cytochrome P450s in gene family CYP3A in Sprague-Dawley rat liver. We compared expression of CYP3A enzymes on postnatal Day 33 (PND33) rats fed casein or soy protein isolate (SPI+)-based AIN-93G diets continuously from gestational Day 4 through PND33 or the diets were switched on PND15 (n = 3-6 litters) to examine the potential imprinting effects of soy on drug metabolism. In addition rats were fed casein, SPI+, SPI+ stripped of phytochemicals (SPI-), or casein diets supplemented with the soy-associated isoflavones genistein or daidzein from weaning through PND33 to examine the hypothesis that the isoflavones are responsible for CYP3A induction by soy feeding. Feeding SPI either continuously or from weaning induced hepatic CYP3A1 and CYP3A2 mRNA, apoprotein, and CYP3A-dependent testosterone 6beta-hydroxylase activity in liver microsomes 2- to 5-fold (P < 0.05). CYP3A mRNA expression was also elevated 2- to 3-fold in the jejunum of SPI-fed rats (P < 0.05). CYP3A was not induced in livers of rats switched to casein from soy at weaning. Induction of CYP3A1 also did not occur in rats fed SPI-, but CYP3A2 mRNA and apoprotein were induced (P < 0.05) in females fed SPI-. Offspring weaned onto genistein-supplemented diets had no elevation of CYP3A mRNAs or apoproteins. Weaning onto daidzein diets increased CYP3A2 mRNA and apoprotein expression in male rats (P < 0.05). These data suggest that early soy consumption may increase the metabolism of a wide variety of CYP3A substrates, but that soy does not imprint the expression of CYP3A enzymes. Effects on CYP3A1 expression appear to be primarily due to phytochemical components of SPI other than isoflavones. In contrast, consumption of soy protein and daidzein appear to be associated with the induction of CYP3A2.

Changes in liver volume from birth to adulthood: a meta-analysis

A diversity of equations is available for the estimation of liver volume (LV), derived from studies in populations of ethnically homogeneous individuals and using a variety of methods of measurement. The aim of this study was to integrate all published pediatric data and to define a general equation for estimating LV from birth onward. Data were collated from 5,036 subjects (birth to 18 yr old). Equations were developed based on simple regression against body surface area (BSA) and multiple regression of LV with weight, height, BSA, age, gender, race, methodology, and year of publication as covariates. These equations, together with those reported in the literature, were compared for accuracy of prediction of LV from birth to 18 yr old. The most parsimonious equation to describe LV was selected according to the Akaike information criteria (AIC), precision and bias and following visual inspection of residual errors and observed vs. predicted plots: LV = 0.722 * BSA(1.176). The multiple regression models indicated that Japanese have up to 19% larger livers compared to Caucasians for a given body weight. Radiographic and ultrasonic measurements were associated with up to 8% lower estimates of liver size compared to measurements made at autopsy. There was no evidence that gender or the year in which a study was published (1933-1999) influenced the estimation of LV. The general equation was also applied to predict adult LV, and its precision and accuracy was found to be superior to those of 10/11 published adult models. In conclusion, we have developed a more general model to predict LV in pediatric populations and young adults, and have investigated a range of covariates.

Population pharmacokinetic studies in pediatrics: issues in design and analysis

The current review addresses the following 3 frequently encountered challenges in the design and analysis of population pharmacokinetic studies in pediatrics: (1) body size adjustments during the development of pharmacostatistical models, (2) design and validation of limited sampling strategies, and (3) the integration of historical priors in data analysis and trial simulation. Size adjustments with empiric approaches based on body weight or body surface area have frequently proven as a pragmatic tool to overcome large size differences in a pediatric study population. Allometric size adjustments, however, provide a more mechanistic, physiologically based approach that, if used a priori, allows delineation of the effect of size from that of other covariates that show a high degree of collinearity. The frequent lack of dense data sets in pediatric clinical pharmacology because of ethical and logistic constraints in study design can be overcome with the application of D-optimality-based limited sampling schemes in combination with Bayesian and nonlinear mixed-effects modeling approaches. Empirically based dose selection and clinical trial designs for pediatric clinical pharmacology studies can be improved by applying clinical trial simulation techniques, especially if they integrate adult and pediatric in vitro and/or in vivo data as historic priors. Although integration of these concepts and techniques in population pharmacokinetic analyses is not only limited to pediatric research, their application allows researchers to overcome some major hurdles frequently encountered in pharmacokinetic studies in pediatrics and, thus, provides the basis for additional clinical pharmacology research in this previously insufficiently studied fraction of the general population.

Diets containing soy protein isolate increase hepatic CYP3A expression and inducibility in weanling male rats exposed during early development

Hepatic CYP3A enzymes were studied in weanling male Sprague-Dawley rats exposed to diets from gestational d 4 in which the sole protein source was either casein (CAS) or soy protein isolate (SPI). At age 25 d, rats were gavaged with corn oil or one of the CYP3A inducers, dexamethasone (DEX) and clotrimazole (CLT), at a dose of 50 mg/kg. Little CYP3A1 (CYP3A23), CYP3A2, or CYP3A9 mRNA was observed in CAS-fed weanling rats but CYP3A18 mRNA was readily detectable in Northern blots. In contrast, consumption of SPI without inducer treatment resulted in the expression of CYP3A1 (CYP3A23), and CYP3A2 mRNAs, expression of CYP3A apoprotein in hepatic microsomes, and a 2-fold greater turnover of the CYP3A substrate midazolam (P < 0.05). DEX induced CYP3A1, CYP3A2, and CYP3A9 (P < 0.05), but not CYP3A18 mRNA expression in rats fed both diets. Hepatic CYP3A apoprotein expression and midazolam 4-hydroxylation in SPI-fed rats was greater than that of CAS-fed rats after DEX treatment (P < 0.05). CLT also induced CYP3A2 mRNA 2-fold in rats fed both diets but CYP3A apoprotein expression in microsomes from SPI-fed CLT rats was double that of CLT-treated rats fed CAS (P < 0.05). The elevation of CYP3A apoprotein due to SPI and the CYP3A apoprotein induction by DEX and CLT treatment yielded no significant diet x inducer interaction. Analysis of heterologous nuclear RNA expression by RT-PCR using intron-specific primers for CYP3A1 revealed a 14-fold increase in RNA transcription in CAS-fed rats after treatment with DEX (P < 0.05) but no increase in rats fed SPI compared with rats fed CAS even though CYP3A1 mRNA and CYP3A apoprotein were significantly elevated. These data demonstrate that exposure to SPI during early development can increase CYP3A expression via post-transcriptional mechanisms and suggest that early soy consumption has potential effects on the metabolism of a wide variety of CYP3A substrates.

Effect of age on in vitro triazolam biotransformation in male human liver microsomes

We studied age-related changes in enzyme kinetic parameters in human liver microsomes (HLMs) in vitro, using triazolam (TRZ), an index of CYP3A activity. HLMs were prepared from male livers from four age groups, n = 5 per group: A (14-20 years), B (21-40 years), C (41-60 years), and D (61-72 years). Mean V(max) values in groups B and C for both 1-hydroxytriazolam (1-OH-TRZ) and 4-hydroxy-triazolam (4-OH-TRZ) formation were significantly greater as compared with groups A and D individually, as well as the net intrinsic clearance (sum of the two pathways). The mean net intrinsic clearance (Cl(int)) values were 25.2, 89.8, 78, and 20.6 nl/min/mg protein in A, B, C, and D, respectively. TRZ Cl(int) correlated well with total CYP3A content (r(s) = 0.84; P < 0.0001). Testosterone (TST) inhibited 1-OH-TRZ formation and activated 4-OH-TRZ formation in all age groups, with no significant differences among the groups; this suggests that the drug-drug interaction potential using TRZ and TST as index CYP3A substrates may not change with age. Reduced V(max) and Cl(int) for TRZ hydroxylation and CYP3A protein in livers from elderly men suggest reduced CYP3A gene expression in this group.