Analysis of Warfarin Therapy in Pediatric Patients: A Prospective Cohort Study of 319 Patients

Pharmacogenomics in Pediatric Patients: Towards Personalized Medicine

It is well known that drug responses differ among patients with regard to dose requirements, efficacy, and adverse drug reactions (ADRs). The differences in drug responses are partially explained by genetic variation. This paper highlights some examples of areas in which the different responses (dose, efficacy, and ADRs) are studied in children, including cancer (cisplatin), thrombosis (vitamin K antagonists), and asthma (long-acting β2 agonists). For childhood cancer, the replication of data is challenging due to a high heterogeneity in study populations, which is mostly due to all the different treatment protocols. For example, the replication cohorts of the association of variants in TPMT and COMT with cisplatin-induced ototoxicity gave conflicting results, possibly as a result of this heterogeneity. For the vitamin K antagonists, the evidence of the association between variants in VKORC1 and CYP2C9 and the dose is clear. Genetic dosing models have been developed, but the implementation is held back by the impossibility of conducting a randomized controlled trial with such a small and diverse population. For the long-acting β2 agonists, there is enough evidence for the association between variant ADRB2 Arg16 and treatment response to start clinical trials to assess clinical value and cost effectiveness of genotyping. However, further research is still needed to define the different asthma phenotypes to study associations in comparable cohorts. These examples show the challenges which are encountered in pediatric pharmacogenomic studies. They also display the importance of collaborations to obtain good quality evidence for the implementation of genetic testing in clinical practice to optimize and personalize treatment.

Effect of CYP2C9, VKORC1, and CYP4F2 polymorphisms on warfarin maintenance dose in children aged less than 18 years: a protocol for systematic review and meta-analysis

BACKGROUND

Despite its shortcomings, warfarin is still the most commonly prescribed anticoagulant to prevent thromboembolism in children. In adults, numerous studies confirmed the robust relationship between warfarin maintenance doses and single nucleotide polymorphisms of cytochrome P450 2C9 (CYP2C9), vitamin K epoxide reductase (VKORC1), and cytochrome P450 4F2 (CYP4F2). However, their effect in children still remains to be determined. The primary objective of the present systematic review and meta-analysis is to assess the effect of genotypes of CYP2C9, VKORC1, and CYP4F2 on warfarin maintenance dose in children.

METHODS/DESIGN

A comprehensive literature review search using the OVID platform will be conducted by a specialized librarian, without language restrictions (i.e., MEDLINE/EMBASE/Cochrane Central Register of Controlled Trials), and all abstracts will be reviewed by two authors. Data abstraction from each eligible study will be extracted individually by two authors (MT and TK), and disagreements will be resolved through discussion with a third person (SI). Critical appraisal of the included analysis of the primary objective will follow the Newcastle-Ottawa Scale, in addition to the Strengthening the Reporting of Genetic Association study (STREGA) statement, and data reporting will follow the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) statement. For the meta-analysis, the presence vs. absence of each genetic polymorphism will be pursued, respectively, using a random effect model with effect size expressed as a mean difference plus 95 % confidence interval.

DISCUSSION

Our study will provide a comprehensive systematic review and meta-analysis on the potential effects of CYP2C9, VKORC1, or CYP4F2 on the warfarin maintenance dose in children, exploring the feasibility of the development of pharmacogenetic-guided warfarin dosing algorithm for children on oral vitamin K antagonists.

SYSTEMATIC REVIEW REGISTRATION

The review has been registered with PROSPERO (registration number CRD42015016172 ).

Safety and Efficacy Outcomes of Home and Hospital Warfarin Management Within a Pediatric Anticoagulation Clinic

The complexity of managing children with chronic disease has led to an increase in the use of long-term warfarin therapy. Time in therapeutic range (TTR) is the preferred method for determining efficacy and stability of warfarin management. This study aimed to determine the TTR achievement and incidence of adverse events among pediatric warfarin patients managed by an anticoagulation clinic over 12 months and to compare TTR achievement between patients self-testing (PST) at home and those monitored using routine methods. International normalized ratio (INR) results reported for 2012 for children currently having their warfarin therapy managed by a dedicated pediatric anticoagulation clinic were analyzed. Warfarin-related adverse events were recorded. A total of 164 patients were included. In total, 93 children performed PST and 71 children tested their INR at a hospital or pathology service. TTR achievement for the cohort was 67.1% (95% confidence interval, 64.4-69.7). A total of 69.2% of INR tests conducted at home were within the TTR compared with 64.3% of INR tests conducted at a hospital or pathology service (P=0.07). One major bleeding event occurred and there was 1 thrombotic episode. PST demonstrated noninferior warfarin stability compared with routine methods. Routine outcome evaluation of pediatric anticoagulation management within single institutions is necessary to confirm the success of such programs.

Timing of low bone mineral density and predictors of bone mineral density trajectory in children on long-term warfarin: a longitudinal study

We studied bone mineral density (BMD) of children exposed to long-term warfarin. BMD Z-scores ≤ -2.0 were estimated to occur in less than one fifth of the patients after 10 years of warfarin exposure, and BMI and growth hormone deficiency predicted BMD changes over time. These predictors can help identify high-risk patients.

INTRODUCTION

Children with chronic diseases are at increased risk of developing thrombosis, which may require long-term warfarin therapy. Warfarin could further jeopardize the bone health of a population already at risk for bone fragility. Our objective was to investigate the occurrence and timing of low bone mineral density (BMD) and the predictors that influence BMD trajectory in children receiving warfarin for >1 year.

METHODS

We analyzed the results of an institutional protocol that includes dual-energy X-ray absorptiometry, with or without spinal X-rays and laboratory biomarkers, as required.

RESULTS

Low BMD (age, sex, race, and height-for-age-Z-score adjusted BMD Z-score ≤ -2.0) was detected in 13 % (9/70) of the patients at some point during their follow-up; these patients were more likely to have complex underlying medical conditions and low body mass index (BMI) percentile. BMD Z-scores remained within normal range in 87 % of children. Survival analysis showed that the estimated 10-year abnormal BMD-free rate for the entire group was 81 % (95 % confidence interval [CI] 69 to 93 %). Trajectory analysis revealed that BMI percentiles at baseline and growth hormone deficiency (GHD) were associated with lower BMD Z-scores at the first assessment, whereas baseline BMI percentile was the only predictor of BMD Z-score over time.

CONCLUSIONS

Our findings identified BMI and GHD as risk factors influencing BMD in children exposed to long-term warfarin, creating an opportunity for early detection and intervention in these patients.

The journey for adolescents and young adults with chronic conditions transitioning to adult care with successful warfarin management

Health transition of youth from a child-centered care model to the adult model has been recognized to be of critical importance due to the increasing numbers of children now surviving chronic conditions. A formalized transition process is required adequately assess the AYA's readiness for transition and to move towards adult care. Indefinite warfarin therapy poses challenges as warfarin is a narrow therapeutic index drug that requires frequent monitoring and attentiveness to warfarin interactions and affects.

OBJECTIVE

The objective of this study was to evaluate transition to adult care for AYAs requiring indefinite warfarin therapy within a structured self-management program.

OUTCOME MEASURES

Results were compared between Phase 1 (enrollment to patient self-management) and Phase 2 (independent warfarin management) 6months following confirmation of transition to adult care. There was no statistical difference between outcome measures except INR testing frequency, and no adverse events.

CONCLUSIONS

This transition process resulted in successful transition as measured by TTR and other clinical end-points from pediatric to adult care. Implementing a formal transition process for young adults with chronic health conditions that considers patient preferences motivates and empowers them over time to develop autonomy with warfarin self-management, results in successful transition and warfarin management.

Pharmacogenomics--how close/far are we to practising individualized medicine for children?

The translation of pharmacogenomics into clinical practice is a key approach for practising individualized medicine, which aims to maximize drug efficacy and minimize drug toxicity. Since the completion of both the Human Genome Project and the International HapMap project, the development of pharmacogenomics has been greatly facilitated. However, progress in translating pharmacogenomics into clinical practice, especially in paediatric medicine, is unexpectedly slow. Many challenges from different areas remain. This paper discusses the existing applications and the limitations to the implementation of paediatric pharmacogenomics, as well as possible solutions for overcoming these limitations and challenges.

Anticoagulants in children and adolescents

Thrombotic complications are increasing at a steady and significant rate in children, resulting in the more widespread use of anticoagulation in this population. Anticoagulant drugs in children can be divided into the older multitargeted agents (heparin, low-molecular-weight heparin, and warfarin) and the newer targeted agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the multitargeted and targeted anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. The various agents differ in their pharmacokinetics, requirements for therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The targeted anticoagulants have properties that may make them more attractive for use in specific clinical situations. Prospective clinical trial data are presented supporting the current and future use of these agents in children.

Anticoagulants in children and adolescents

Thrombotic complications are increasing at a steady and significant rate in children, resulting in the more widespread use of anticoagulation in this population. Anticoagulant drugs in children can be divided into the older multitargeted agents (heparin, low-molecular-weight heparin, and warfarin) and the newer targeted agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the multitargeted and targeted anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. The various agents differ in their pharmacokinetics, requirements for therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The targeted anticoagulants have properties that may make them more attractive for use in specific clinical situations. Prospective clinical trial data are presented supporting the current and future use of these agents in children.

Strategies for thromboprophylaxis in Fontan circulation: a meta-analysis

BACKGROUND

The Fontan circulation is associated with an increased risk of thromboembolic events (TEs). As many as 25% of these thrombotic events result in fatality. More subtle adverse effects on the pulmonary circulation from embolic thrombi may further impair adequate functioning of the circuit. Despite these well-documented phenomena, the most optimal approaches to thromboprophylaxis are still not clearly defined.

OBJECTIVE

A meta-analysis of published trials in English on PubMed and Cochrane libraries that evaluated the role of using TE prophylaxis in patients who underwent the Fontan procedure was conducted.

METHODS

10 studies with a total number of 1200 patients with an average follow-up time of 7.1 years were identified. A random effect model was used.

RESULTS

The incidence of TE was significantly less in patients who received TE prophylaxis (using either aspirin or warfarin) compared with patients who did not receive TE prophylaxis (OR 0.425, 95% CI 0.194 to 0.929, p<0.01, I(2)=37%). The incidence of TE was significantly lower in patients who received aspirin compared with no TE prophylaxis (OR 0.363, 95% CI 0.177 to 0.744, p<0.01, I(2)=0%) and who received warfarin compared with no TE prophylaxis (OR 0.327, 95% CI 0.168 to 0.634, p<0.01, I(2)=2.5%). There was no significant difference in incidence of TE between warfarin and aspirin (OR 0.936, 95% CI 0.609 to 1.438, p=0.54, I(2)=0%). Furthermore, there was no significant difference in incidence of early TE (within 6 months of the operation) or late TE (>6 months) between patients receiving warfarin and aspirin (OR 0.784, 95% CI 0.310 to 1.982, p=0.37, I(2)=8%) and (OR 0.776, 95% CI 0.249 to 2.42, p=0.3, I(2)=45%), respectively. When only total cavopulmonary connection patients were included, there was again no difference between warfarin and aspirin in the incidence of TE (OR 0.813, 95% CI 0.471 to 1.401, p=0.34, I(2)=11%).

CONCLUSIONS

This study shows a significantly lower incidence of TE after Fontan procedure if either aspirin or warfarin is used. This meta-analysis suggests no significant difference in incidence of early or late TE in patients receiving aspirin compared with warfarin.

A guide to the use of anticoagulant drugs in children

Increasing thrombotic complications in children with complex medication conditions have led to more widespread use of anticoagulants [Raffini et al. in Pediatrics 124(4):1001-8, 2009]. While current guidelines for the management of antithrombotic therapy in neonates and children exist, they are based on low- and very low-quality evidence [Monagle et al. in Chest 141(2 Suppl):e737-801S, 2012]. Despite numerous differences, current anticoagulation practice is largely extrapolated from adult studies. This is sub-optimal, particularly in neonates who have a rapidly evolving hemostatic system. The majority of pediatric patients have underlying medical conditions that may significantly influence drug choice and bleeding risk. This article reviews the use of anticoagulants in children with thrombosis, focusing on practical aspects such as dosing, monitoring, and complications. Low molecular weight heparin has become the preferred anticoagulant in children, although unfractionated heparin and warfarin remain frequently used. Other anticoagulants, including fondaparinux, direct thrombin inhibitors, and the newer target-specific oral anticoagulants are also discussed. Given the many unique challenges surrounding the use of anticoagulants in children, pediatric hospitals should have written practice guidelines as well as experienced providers to care for children with thrombosis. This is an evolving field, and further studies of the use of anticoagulants in neonates and children are greatly needed to help optimize care.

Bone density in children with single ventricle physiology

Children with chronic diseases are at risk for low bone mineral density (BMD). There are no studies of BMD in children with congenital heart disease and particularly single ventricle (SV). Children with this defect are often treated with warfarin, suspected to negatively impact BMD in adults. We assessed BMD in patients with SV physiology and compared the BMD of subjects taking warfarin to those who were not. Subjects 5-12 years with SV were included. BMD z scores by dual-energy X-ray absorptiometry of the spine and total body less head (TBLH) were obtained. Calcium intake, activity level, height, and Tanner stage were assessed. Linear regression models and t tests were used to investigate differences between participants and normative data as well as between subjects' subgroups. Twenty-six subjects were included and 16 took warfarin. Mean BMD z score at the spine was significantly lower than expected at -1.0 ± 0.2 (p < 0.0001), as was the BMD z score for TBLH at -0.8 ± 0.2 (p < 0.0001). Those results remained significant after adjusting for height. Subjects who were on warfarin tended to have lower BMD at both the spine and TBLH than those who were not, with a z score difference of 0.6 ± 0.46 at the spine (p = 0.106) and a difference of 0.4 ± 0.34 at TBLH (p = 0.132). BMD is significantly reduced in children with SV. Warfarin appears to lower BMD but the effect is less conclusive. Continued evaluation is recommended for these patients at risk for reduced bone density. Evaluation of other cardiac patients on warfarin therapy should also be considered.

Mechanical circulatory support: balancing bleeding and clotting in high-risk patients

Mechanical circulatory support (MCS) provides a bridge to heart transplant in children and adults with life-threatening heart failure and sustains patients ineligible for transplant. Extracorporeal membrane oxygenation (ECMO) provides temporary support for patients in cardiac or pulmonary failure through external gas exchange and continuous flow of blood. Because the median time to heart transplant exceeds event-free time on ECMO, pulsatile left ventricular assist devices (LVADs) are used to support infants and children. Continuous flow LVADs are preferred in adolescents and adults due to increased pump durability and improved overall survival. The shear stress created by the mechanical pumps cause changes in the hematologic system; acquired von Willebrand syndrome occurs in almost all patients treated with MCS. Despite the improvements in survival, major bleeding occurs in one-third of patients with a LVAD and ischemic stroke and LVAD thrombosis can affect 12% of adults and 29% of children. An antithrombotic strategy to mitigate LVAD bleeding and thrombotic complications has been tested in a randomized trial in children, but intensity of antithrombotic therapy in adults varies widely. Consensus guidelines for antithrombotic therapy during ECMO were created due to significant differences in management across centers. Because of the high risk for both bleeding and thrombotic complications, experts in hemostasis can significantly impact care of patients requiring mechanical circulatory support and are a necessary part of the management team.

Pharmacogenetics of warfarin in a paediatric population: time in therapeutic range, initial and stable dosing and adverse effects

Warfarin is used in paediatric populations, but dosing algorithms incorporating pharmacogenetic data have not been developed for children. Previous studies have produced estimates of the effect of polymorphisms in Cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex subunit 1 (VKORC1) on stable warfarin dosing, but data on time in therapeutic range, initial dosing and adverse effects are limited. Participants (n=97) were recruited, and routine clinical data and salivary DNA samples were collected from all participants and analysed for CYP2C9*2, *3 and VKORC1-1639 polymorphisms.VKORC1 -1639 was associated with a greater proportion of the first 6 months' treatment time spent within the target International Normalised Ratio (INR) range, accounting for an additional 9.5% of the variance in the proportion of time. CYP2C9*2 was associated with a greater likelihood of INR values exceeding the target range during the initiation of treatment (odds ratio (OR; per additional copy) 4.18, 95% confidence interval (CI) 1.42, 12.34). CYP2C9*2 and VKORC1-1639 were associated with a lower dose requirement, and accounted for almost 12% of the variance in stable dose. VKORC1-1639 was associated with an increased likelihood of mild bleeding complications (OR (heterozygotes vs homozygotes) 4.53, 95% CI 1.59, 12.93). These data show novel associations between VKORC1-1639 and CYP2C9*2 and INR values in children taking warfarin, as well as replicating previous findings with regard to stable dose requirements. The development of pharmacogenomic dosing algorithms for children using warfarin has the potential to improve clinical care in this population.

Response to warfarin therapy in obese pediatric patients dosed according to institutional guidelines

BACKGROUND

Current warfarin dosing guidelines for pediatric patients do not account for obesity. Published data from adults suggest that obesity may affect warfarin dosing requirements. Obesity is prevalent in the pediatric population, and current warfarin dosing methods should be evaluated in obese pediatric patients.

METHODS

Patients aged 2 to 18 years who were obese and initiated on warfarin therapy at our institution as inpatients from 2004 to 2010 were identified and matched in a 1:2 ratio by age and sex with nonobese patients who were initiated on warfarin therapy. Patients were categorized obese per Centers for Disease Control guidelines. Demographic and disease state information, warfarin dosing information, INR values, and interacting medications were collected. Warfarin was dosed according to the institutional guidelines adapted from the published literature. Time to therapeutic INR value was the primary endpoint and percent of patients with supratherapeutic INR values was the secondary endpoint.

RESULTS

A total of 30 patients met the study criteria (10 obese, 20 nonobese), and baseline demographic variables were similar. No significant differences were noted in the number of INR values drawn, number of warfarin doses administered, or length of stay. Initial and maximum doses of warfarin per kg were significantly lower in obese patients compared with nonobese patients (P<0.05). Median time to therapeutic INR value was twice as long in obese patients as in nonobese patients (median=6 [range, 4 to 28 d] versus median=3 [range, 1 to 10 d]; P<0.01).

CONCLUSIONS

Obese pediatric patients have an increased time to therapeutic INR value when traditional warfarin dosing guidelines are used.

Pharmacogenetics-based warfarin dosing in children

Clinical factors, demographic variables and variations in two genes, CYP2C9 and VKORC1, have been shown to contribute to the variability in warfarin dose requirements among adult patients. Less is known about their relative importance for dose variability in children. A few small studies have been reported, but the results have been conflicting, especially regarding the impact of genotypes. In this article, we critically review published pharmacogenetic-based prediction models for warfarin dosing in children, and present results from a head-to-head comparison of predictive performance in a distinct cohort of warfarin-treated children. Finally we discuss what properties a prediction model should have, and what knowledge gaps need to be filled, to improve warfarin therapy in children of all ages.

Pharmacokinetics and pharmacodynamics of anticoagulants in paediatric patients

Given the rising incidence of thrombotic complications in paediatric patients, understanding of the pharmacologic behaviour of anticoagulant drugs in children has gained importance. Significant developmental differences between children and adults in the haemostatic system and pharmacologic parameters for individual drugs highlight potentially unique aspects of anticoagulant pharmacology in this special and vulnerable population. This review focuses on pharmacologic information relevant to the dosing of unfractionated heparin, low molecular weight heparin, warfarin, bivalirudin, argatroban and fondaparinux in paediatric patients. The bulk of clinical experience with paediatric anticoagulation rests with the first three of these agents, each of which requires higher bodyweight-based dosing for the youngest patients, compared with adults, in order to achieve comparable pharmacodynamic effects, likely related to an inverse correlation between age and bodyweight-normalized clearance of these drugs. Whether extrapolation of therapeutic ranges targeted for adult patients prescribed these agents is valid for children, however, is unknown and a high priority for future research. Novel oral anticoagulants, such as dabigatran, rivaroxaban and apixaban, hold promise for future use in paediatrics but require further pharmacologic study in infants, children and adolescents.

VKORC1 and CYP2C9 genotypes are predictors of warfarin-related outcomes in children

BACKGROUND

Despite substantial evidence supporting a pharmacogenetic approach to warfarin therapy in adults, evidence on the importance of genetics in warfarin therapy in children is limited, particularly for clinical outcomes. We assessed the contribution of CYP2C9/VKORC1/CYP4F2 genotypes and variation in other genes involved in vitamin K and coagulation pathways to warfarin dose and related clinical outcomes in children.

PROCEDURE

Clinical and genetic data for 93 children (age ≤ 18 years) who received warfarin therapy were obtained. DNA was genotyped for 93 selected single nucleotide polymorphisms using a custom assay.

RESULTS

With a median age of 4.8 years, our cohort included more young children than most previous studies. Overall, 76.3% of dose variability was explained by weight, indication, VKORC1-1639G/A and CYP2C9 *2/*3, with genotypes accounting for 21.1% of variability. There was a strong correlation (R(2) = 0.68; P < 0.001) between actual and predicted warfarin dose using a pediatric genotype-based dosing model. VKORC1 genotype had a significant impact on time to therapeutic international normalized ratio (INR) (P = 0.047) and time to over-anticoagulation (INR > 4; P = 0.024) during the initiation of therapy. CYP2C9*3 carriers were also at increased risk of major bleeding while receiving warfarin (adjusted OR = 11.28). An additional variant in CYP2C9 (rs7089580) was significantly associated with warfarin dose (P = 0.020) in a multivariate clinical and genetic model.

CONCLUSIONS

This study confirms the importance of VKORC1/CYP2C9 genotypes for warfarin dosing in a young pediatric cohort and demonstrates an impact of genetic factors on clinical outcomes in children. Furthermore, we identified an additional variant in CYP2C9 of potential relevance for warfarin dosing in children.

Describing the profile of patients on concurrent rifampin and warfarin therapy in western Kenya: a case series

Background

Rifampicin’s ability to induce hepatic enzymes is responsible for causing a clinically significant drug interaction with warfarin. Little data exists to guide clinicians on managing this interaction, especially in Sub-Saharan Africa where many patients are exposed to this combination due to a higher burden of tuberculosis.

Objective

The objective of the case series is to provide insight to practicing clinicians of the unique dynamics of this drug interaction in resource-constrained settings. The case series will provide details on commonly encountered scenarios and the dosage adjustments required to maintain a therapeutic INR.

Methods

A retrospective chart review was conducted of patients attending the Moi Teaching and Referral Hospital anticoagulation clinic in Eldoret, Kenya. Patients were included if they had a history of concurrent rifampicin and warfarin therapy and a minimum follow up of 2 months. Descriptive statistics were used to explain the demographic characteristics, time to therapeutic INR and average weekly warfarin dose. The inference on proportions test was conducted to compare the time in the therapeutic range (TTR) for patients on concurrent rifampicin to the rest of the patients not receiving rifampicin in the clinic.

Results

Of the 350 patient charts evaluated, 10 met the inclusion criteria. The median percentage increase of the weekly warfarin dose from baseline was 15.7 %. For the patients in this analysis, the median TTR was 47 %.

Discussion

Patients on concurrent therapy should be rigorously monitored with regular INR checks and warfarin dosage adjustments. Empiric dosage adjustments of warfarin should be avoided but patient characteristics can aid in understanding the alterations seen in INR.

Current and future antithrombotic agents in children

Thromboembolic complications are increasing in children, and the use of anticoagulation has seen a dramatic increase despite the lack of randomized clinical trials. The most widely used agents in children are heparin and warfarin, however these agents have limitations that are exaggerated in children. This has led to the use of newer agents with improved pharmacologic properties such as low-molecular-weight heparin, however, the use of novel agents such as direct thrombin inhibitors has been limited to case reports. These agents, however, have potential advantages over heparin, low-molecular-weight heparin and warfarin. Current clinical trials are in progress to define the proper dose of two such agents--argatroban (Argatroban, GlaxoSmithKline) and bivalirudin (Angiomax, The Medicines Company). The selective Factor Xa inhibitor fondaparinux (Arixtra, Sanofi-Synthelabo) has not been used in children; however, there are situations in which this agent may be advantageous. This review will discuss the currently available agents, with an emphasis on those that are novel and their potential uses in children.

Pharmacogenomics and pharmacoepigenomics in pediatric medicine

In the past several years, human genetics studies have progressed from monogenic to complex and common diseases because of the advancement in technologies. There is increased knowledge of the pharmacokinetics and pharmacogenomics of the drugs in adults as well as in children. These technological developments provided new diagnostic, prognostic, and therapeutic opportunities. We are now in a position to address many additional ambitious questions. For instance, in clinical medicine, interindividual variation in drug response is a major problem. Some of the heterogeneity of drug safety and efficacy among individuals can be explained by pharmacogenomics. It has also the potential to improve the treatment in both adults and children. In pediatrics however, there is ontogeny and metabolic capacity in children is different compared to adults. Several specific developmental changes may underlie some of the variability in drug response seen in children. They may also be responsible for adverse drug reactions (ADRs). Therefore, much of the diversity in drug effects cannot be explained by studying the genomic diversity alone. It is necessary to include the effect of growth (involves variations in gene expression) along with genetic differences when explaining the variability in treatment response. In this respect epigenomics may expand the scope of pharmacogenomics towards optimization of drug therapy. Future studies must focus on periods of maturation of the drug-metabolizing enzymes and polymorphisms in their genes by using candidate gene approach, gene expression analysis, genome-wide haplotype mapping, and proteomics. The integration of genetic data and clinical phenotypes along with the role of other factors is necessary to evaluate both efficacy and ADRs of any drug. It may require extensive genetic epidemiological studies spanning over many years.

Genetics-based pediatric warfarin dosage regimen derived using pharmacometric bridging

BACKGROUND

Warfarin dosage regimens using CYP2C9 and VKORC1 polymorphisms have been extensively studied in adults and is included in US Food and Drug Administration-approved warfarin labeling. However, no dosage algorithm is available for pediatric patients.

OBJECTIVE

To derive a genetics-based pediatric dosge regimen for warfarin, including starting dose and titration scheme.

METHODS

A model-based approach was developed based on a previously validated warfarin dosage model in adults, with subsequent comparison to pediatric data from pediatric warfarin dose, genotyping, and international normalized ratio (INR) results. The adult model was based on a previously established model from the CROWN (CReating an Optimal Warfarin dosing Nomogram) trial. Pediatric warfarin data were obtained from a study conducted at the Children's Hospital of Los Angeles with 26 subjects. Variant alleles of CYP2C9 (rs1799853 or *2, and rs1057910 or *3) and the VKORC1 single nucleotide polymorphism (SNP) rs9923231 (-1639 G>A) were assessed, where the rs numbers are reference SNP identification tags assigned by the National Center for Biotechnology Information.

RESULTS

A pediatric warfarin model was derived using the previously validated model and clinical pharmacology considerations. The model was validated, and clinical trial simulation and stochastic modeling were used to optimize pediatric dosage and titration. The final dosage regimen was optimized based on simulations targeting a high (≥60%) proportion of INRs within the therapeutic range by week 2 of warfarin therapy while minimizing INRs >3.5 or <2.

CONCLUSIONS

The proposed pediatric warfarin dosage scheme based on individual CYP2C9 (alleles *1,*2,*3) and VKORC1 rs9923231 (-1639 G>A) genotypes may offer improved dosage compared to current treatment strategies, especially in patients with variant CYP2C9 and VKORC1 alleles. This pilot study provides the foundation for a larger prospective evaluation of genetics-based warfarin dosage in pediatric patients.

Readmissions for warfarin-related bleeding in pediatric patients after hospital discharge

BACKGROUND

Warfarin therapy in pediatric patients can be difficult to manage with bleeding as a primary adverse event. Therapy initiation can be difficult as doses to achieve therapeutic outcomes are being determined. Evaluation of readmission for bleeding in pediatric patients discharged on warfarin therapy may be useful to prevent adverse events.

METHODS

The Pediatric Health Information System (PHIS) was queried to identify all patients <19 years of age who were discharged from a pediatric hospital on warfarin therapy. Patients who were readmitted with bleeding in the first 30 days after discharge were identified and patient variables, hospital stay variables, and medications at discharge were identified. Univariate and multivariate analysis was performed to identify independent risk factors for bleeding readmission.

RESULTS

A total of 4,883 patients met study criteria (56% male, mean age 10.1 + 5.9 years). The two most common indications for warfarin therapy were cardiac valve replacement (23.6%) and Fontan procedure (19.5%). Ninety-seven patients (1.99%) were readmitted with bleeding within 30 days of discharge [median time 9 days (IQR 5-16 days)]. Multivariate analysis identified Asian race (OR 4.0, P < 0.01); mitral valve replacement (OR 2.5, P < 0.01); escitalopram at discharge (OR 4.2, P = 0.02); levofloxacin at discharge (OR 8.3, P < 0.01); lansoprazole at discharge (OR 1.7, P = 0.047); and length of stay (OR 1.01, P = 0.047) as significant for bleeding readmission.

CONCLUSION

Pediatric patients discharged on warfarin may be readmitted for bleeding within 30 days if risk factors are present. Risk factors include patient genetic profile, drug interactions, and indications with higher goal INR values.

Warfarin pharmacogenomics in children

Warfarin is the most commonly used oral anticoagulant worldwide. Warfarin has a narrow therapeutic index, requiring frequent monitoring of the INR to achieve therapeutic anticoagulation. The role of pharmacogenomics in warfarin disposition and response has been well established in adults, but remains unclear for pediatric patients. In this review, we focus on the important CYP2C9 and VKORC1 variants involved in warfarin response, our current understanding of warfarin disposition and pharmacogenomics, and recent warfarin pharmacogenetic studies in pediatric patients. Finally, we discuss the need for future pediatric studies and the clinical implications of developing pharmacogenetic-based dosing algorithms in children.

The economic costs of routine INR monitoring in infants and children--examining point-of-care devices used within the home setting compared to traditional anticoagulation clinic monitoring

INTRODUCTION

The use of point-of-care (POC) devices within the home for routine INR monitoring has demonstrated reliability, safety and effectiveness in the management of infants and children requiring long-term warfarin therapy. However, a comprehensive cost-analysis of using this method of management, compared to attending anticoagulation clinics has not been reported. The aim of this study was to compare the estimated societal costs of attending anticoagulation clinics for routine INR monitoring to using a POC test in the home.

MATERIALS AND METHODS

This study used a comparative before-and-after design that included 60 infants and children managed via the Haematology department at a tertiary paediatric centre. Each participant was exposed to both modes of management at various times for a period of ≥3 months. A questionnaire, consisting of 25 questions was sent to families to complete and return. Data collected included: the frequency of monitoring, mode of travel to and from clinics, total time consumed, and primary carer's income level.

RESULTS

The home monitoring cohort saved a total of 1 hour 19 minutes per INR test compared to attending anticoagulation clinics and had a cost saving to society of $66.83 (AUD) per INR test compared to traditional care; incorporating health sector costs, travel expenses and lost time.

CONCLUSIONS

The traditional model of care requires a considerable investment of time per test from both child and carer. Home INR monitoring in infants and children provides greater societal economic benefits compared to traditional models.

Genetic and clinical determinants influencing warfarin dosing in children with heart disease

Warfarin is a common anticoagulant with narrow therapeutic window and variable anticoagulation effects. Single gene polymorphisms in cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase (VKORC1) have been shown to impact warfarin dosing in adults. Insufficient data exists on genetic and clinical factors which influence warfarin dosing in children. Pediatric patients with heart disease who received long-term warfarin therapy were tested for VKORC1 and CYP2C9 polymorphisms. Clinical and demographic data were reviewed in those children who achieved stable therapeutic international normalized ratio (INR). Multiple linear regression modeling was used to assess relationships between stable warfarin doses and genetic or clinical variables. Fifty children were tested for VKORC1 and CYP2C9 polymorphisms; 37 patients (M 26: F 11) had complete data, achieved stable therapeutic INR, and were included in dose variability analysis. There were predominance of white race 73% and male sex 70.3%. The mean age was 9.6 years (1.8-18.6 years). The mean weight was 37.8 kg (7.7-95 kg). Fontan physiology and mechanical cardiac valves were two most common indications for chronic warfarin therapy (25/37 or 67.6%). Twelve patients (32.4%) had ≥ 2 indications for warfarin therapy. Three patients had documented venous or arterial clots, and 5 patients had strokes. Congenital heart disease was present in 29 patients (78.4%), including Fontan physiology (20), complex biventricular physiology (4), and congenital mitral valve disease (5). Acquired heart disease was present in 8 patients (21.6%), including Kawasaki disease with coronary aneurysms (3), acquired mitral valve disease (3), and Marfan syndrome (2). Stable warfarin dose (mg/kg/day) was strongly associated with VKORC1 polymorphism (p < 0.0001) and goal therapeutic INR (p = 0.009). Negative correlations were observed between stable warfarin dose and age, weight, height, and BSA (p = 0.04, 0.02, 0.02, and 0.02 respectively). Factors which did not influence warfarin dose included CYP2C9 polymorphism (p = 0.17), concurrent medications (p = 0.85), sex (p = 0.4), race (p = 0.14), congenital heart disease (p = 0.09), and Fontan physiology (p = 0.76). The gene-dose effect was observed in children with homozygous wild type VKORC1 CC, who required higher warfarin dose compared to those carrying heterozygous TC or homozygous TT (p = 0.028 and 0.0004 respectively). The full multiple linear regression model revealed that VKORC1 genotypes accounted for 47% of dosing variability; CYPC29 accounted for 5%. Overall, the combination of VKORC1, CYP2C9, age, and target INR accounted for 82% of dosing variability. In children with heart disease, VKORC1 genotypes, age, and target INR are important determinants influencing warfarin dosing in children with heart disease. Future warfarin dosing algorithm in children should factor both genetic and clinical factors.

Warfarin anticoagulation after congenital heart surgery at a large children's hospital

Management of warfarin in pediatric patients remains a clinical challenge. Warfarin may be administered after congenital heart surgery, and the risks of morbidity can be high. Currently, no data exist to describe the initiation of warfarin and the risk factors for morbidity in post-congenital heart surgery patients. This study aimed to characterize the time required to reach anticoagulation for patients administered warfarin therapy after cardiac surgery and to identify and characterize the risk factors for supratherapeutic anticoagulation and adverse events after warfarin initiation. This retrospective study reviewed all patients between 2006 and 2011 who received warfarin anticoagulation after cardiac surgery at our institution. Factors associated with a prolonged time required to reach an international normalized ratio (INR) of 2 and factors related to supratherapeutic anticoagulation (INR ≥ 4) were identified. The inclusion criteria were met by 59 patients. The median time required to reach an INR of at least 2 after initiation of warfarin was 2 days (interquartile range (IQR), 2-4). The only groups that required a significantly longer time to reach an INR of 2 were those with a postoperative delay in initiation of warfarin and those receiving heparin anticoagulation before and during warfarin initiation. Nine patients experienced an INR of 4 or more. However, no thrombotic events occurred, and significant bleeding was uncommon. In the largest reported group of patients undergoing anticoagulation after cardiac surgery, warfarin was well tolerated across all age groups. The median time required to reach an INR of 2 after loading with warfarin was 2 days, and adverse events were uncommon.

Thrombotic complications and thromboprophylaxis across all three stages of single ventricle heart palliation

OBJECTIVES

To describe the incidence of thrombotic complications across all 3 stages of single ventricle palliation and the association between thromboprophylaxis use and thrombotic risk.

STUDY DESIGN

Two separate cross-sectional studies were performed that included 195 patients born between 2003-2008 and 162 patients who underwent Fontan after 2000.

RESULTS

The incidence of thrombotic complications was 40% and 28% after initial palliation and superior cavopulmonary connection (SCPC), respectively; 5-year freedom from thrombotic complications after Fontan was 79%. Thromboprophylaxis was initiated for 70%, 46%, and 94% of patients after initial palliation, SCPC, and Fontan, respectively. Thromboprophylaxis with enoxaparin (vs no thromboprophylaxis) was associated with a reduction in risk of thrombotic complications after initial palliation (hazard ratio [HR] 0.5, P = .05) and SCPC (HR 0.2, P = .04). Thromboprophylaxis with warfarin was associated with a reduction in thrombotic complications after Fontan (HR 0.27, P = .05 vs acetylsalicylic acid; HR 0.18, P = .02 vs no thromboprophylaxis). Thrombotic complications were associated with increased mortality after initial palliation (HR 5.5, P < .001) and SCPC (HR 12.5, P < .001). Three patients experienced major bleeding complications without permanent sequelae (2 enoxaparin, 1 warfarin).

CONCLUSIONS

Given the negative impact of thrombotic complications on survival, the low risk of serious bleeding complications, and the association between thromboprophylaxis and lowered thrombotic complication risk across all 3 palliative stages, routine use of thromboprophylaxis from the initial palliation to the early post-Fontan period in this population may be indicated.

Pulmonary embolism in children

Unlike in adults, pulmonary embolism (PE) is an infrequent event in children. It has a marked bimodal distribution during the paediatric years, occurring predominantly in neonates and adolescents. The most important predisposing factors to PE in children are the presence of a central venous line (CVL), infection, and congenital heart disease. Clinical signs of PE are non-specific in children or can be masked by underlying conditions. Diagnostic testing is necessary in children, especially with the lack of clinical prediction rules. Recommendations for tests are derived from adult studies with ventilation/perfusion (V/Q) scintigraphy being well established. There exists an increasing role for computerised tomography pulmonary angiography (CTPA) and magnetic resonance pulmonary angiography (MRPA). Thrombotic events in children are initially treated with unfractionated heparin (UFH) or low molecular weight heparin (LMWH). For the extended anticoagulant therapy LMWH or vitamin K antagonists can be used with duration of treatment recommendations extrapolated from adult data. Mortality rates for PE in children are reported to be around 10%, with death usually related to the underlying disease processes. Exact data about recurrence risk in children is unknown. Because of the difference in aetiology, presentation, diagnostic methods and treatment between adults and children further research is necessary to assess the validity of recommendations for children.

Risk factors for elevated INR values during warfarin therapy in hospitalized pediatric patients

BACKGROUND

There are currently no data describing the incidence of or risk factors for elevated International Normalized Ratio (INR) values in patients receiving warfarin at a tertiary care pediatric hospital. By minimizing risk factors for elevated INR values patient morbidity may be minimized.

PROCEDURES

A 6-year retrospective chart review of inpatient admissions at our institution that received warfarin was performed. Factors for elevated INR values, such as patient demographics, disease state, and medication interactions were reviewed. Patients with an INR value ≥ 0.5 above the upper limit of the goal range were compared to patients without an elevated INR value. A logistic regression analysis was performed to identify independent variables for elevated INR values.

RESULTS

A total of 298 patient admissions (184 patients) met study criteria, and the largest patient population was between 1 and 12 years old (36.9%). The most common indication for warfarin was mitral valve replacement (25.5%). An elevated INR occurred in 20.8% of admissions. Logistic regression analysis identified Asian race, an elevated baseline INR value, warfarin initiation after cardiac surgery, days of inpatient warfarin therapy, and drug interactions with ciprofloxacin and lansoprazole as independent variables for an elevated INR value (P < 0.05). Obesity was significant as an independent variable for a non-elevated INR value (P < 0.05).

CONCLUSIONS

Elevated INR values occur often in patients receiving warfarin while admitted to a tertiary care pediatric facility and modifiable risk factors exist for elevated INR values.

Natural Health Product Utilization in Warfarinized Children; Prevalence and Knowledge

Background:

The need for long-term thromboprophylaxis in children using warfarin therapy is increasing. Natural health products (NHPs) are administered to children by parents who perceive them to be useful and acceptable adjuncts or alternatives to conventional therapies. Interactions of NHPs with prescribed therapies may result in serious adverse events. NHP usage is underevaluated in children and there are no studies evaluating NHP usage in warfarinized children.

Objectives:

To explore NHP use in warfarinized children and their siblings to determine the prevalence, varieties, and reasons for NHP usage, as well as the potential effect on warfarinization (eg, time in therapeutic range [TTR]).

Methods:

This is a 3-phase cross-sectional cohort study that includes the (1) prevalence (2) NHP education and knowledge assessment, and (3) the follow-up NHP utilization phase.

Results:

Forty-six percent of warfarinized children consumed NHPs, with time in therapeutic range of 74%. The mean score for baseline knowledge of NHPs and warfarin following the education phase was 67%. Follow-up NHP use was 30%, and increased consistency of utilization with TTR was 83% (p < 0.05), consistent with education provided.

Conclusions:

The consistent prevalence rates over time of NHP usage in warfarinized children indicate the need for future studies. Education remains vital to combat the potential risks of NHP-warfarin interaction, encouraging patient disclosure and consistency.

Vitamin k antagonist warfarin for palliative treatment of metachromatic leukodystrophy, a compassionate study of four subjects

MLD is characterized by accumulation of sulfatides in the brain. Vitamin K regulates two enzymes in sphingolipid biosynthesis and warfarin is known to lower brain sulfatides in rats and mice. We hypothesized that warfarin may mitigate the MLD phenotype by reducing the formation of sulfatides. This compassionate study recruited four advanced patients with clinical, biochemical and genetic confirmation of MLD. The patients were treated with warfarin according to the approved protocol for a total of 45 days. The battery of tests included proton MR spectroscopy (H-MRS) of brain and urinary sulfatide levels recorded at defined intervals. The patients tolerated the medication and there were no bleeding complications.

The urinary sulfatide levels did not decline during the study period. The H-MRS showed decreased N-acetyl aspartate and elevated myoinositol levels in the basal ganglia which remained unchanged after treatment.

Our study did not demonstrate any beneficial effects of warfarin in four advanced cases of MLD. The drug intervention however, was safe and deserves further evaluation through a larger study of longer duration. The metabolite abnormalities reported on H-MRS may be useful in longitudinal follow up of patients with MLD during drug trials.

Antithrombotic therapy in neonates and children: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines

BACKGROUND

Neonates and children differ from adults in physiology, pharmacologic responses to drugs, epidemiology, and long-term consequences of thrombosis. This guideline addresses optimal strategies for the management of thrombosis in neonates and children.

METHODS

The methods of this guideline follow those described in the Methodology for the Development of Antithrombotic Therapy and Prevention of Thrombosis Guidelines: Antithrombotic Therapy and Prevention of Thrombosis, 9th ed: American College of Chest Physicians Evidence-Based Clinical Practice Guidelines.

RESULTS

We suggest that where possible, pediatric hematologists with experience in thromboembolism manage pediatric patients with thromboembolism (Grade 2C). When this is not possible, we suggest a combination of a neonatologist/pediatrician and adult hematologist supported by consultation with an experienced pediatric hematologist (Grade 2C). We suggest that therapeutic unfractionated heparin in children is titrated to achieve a target anti-Xa range of 0.35 to 0.7 units/mL or an activated partial thromboplastin time range that correlates to this anti-Xa range or to a protamine titration range of 0.2 to 0.4 units/mL (Grade 2C). For neonates and children receiving either daily or bid therapeutic low-molecular-weight heparin, we suggest that the drug be monitored to a target range of 0.5 to 1.0 units/mL in a sample taken 4 to 6 h after subcutaneous injection or, alternatively, 0.5 to 0.8 units/mL in a sample taken 2 to 6 h after subcutaneous injection (Grade 2C).

CONCLUSIONS

The evidence supporting most recommendations for antithrombotic therapy in neonates and children remains weak. Studies addressing appropriate drug target ranges and monitoring requirements are urgently required in addition to site- and clinical situation-specific thrombosis management strategies.

Development of biomarkers to optimize pediatric patient management: what makes children different?

Despite the frequent utilization of biomarkers in medical practice, there is a relative paucity of information regarding validated pediatric biomarkers. Frequently, biomarkers found to be efficacious in adults are extrapolated to the pediatric clinical setting without considering that the pathogenesis of many diseases is distinctly different in children, and ontogeny directly influences disease evolution and therapeutic response in children. New and innovative approaches are necessary to provide reliable, validated biomarkers that can be used to improve and advance pediatric medical care.

Safety of anticoagulants in children with arterial ischemic stroke

Pediatric arterial ischemic stroke (AIS) is increasingly diagnosed and carries significant risks of recurrence, morbidity, and mortality. Anticoagulant therapy (ACT) is commonly prescribed in childhood AIS. Hemorrhagic complication rates in pediatric stroke are unknown, and adult safety data are of limited applicability. We analyzed a prospectively enrolled cohort of children (aged 1 month-18 years) with acute AIS selected using standardized criteria for protocol-based ACT over14-year period. We assessed ACT-associated intracranial hemorrhage (ICH), including frequency, clinical and radiologic characteristics, predictors, and outcome. Among 215 children with AIS, 123 received ACT within 7 days after diagnosis. During anticoagulation, 14 (11%) children developed new or increased ICH, all within 26 days from diagnosis. ICH was symptomatic in 5 (4%), asymptomatic in 9 (7%), and mild (European Cooperative Acute Stroke Study grades HI1 or HI2) in all but 1 child (ECASS PH-2). Long-term neurologic outcomes after ACT-associated ICH in survivors were abnormal in 73% (8/11). Comparably, 12 of 75 (16%) children treated without anticoagulation developed new or increased ICH on follow-up imaging (P = .3507). We conclude that ACT is relatively safe in children with AIS, with a 4% risk of symptomatic ICH. Based on the safety of ACT in our study, clinical trials of ACT in childhood AIS are warranted.

Old and new antithrombotic drugs in neonates and infants

Thromboembolic complications are becoming more frequent in children and the use of anticoagulation has increased considerably. The most widely used agents in children, heparin, low molecular weight heparin, and warfarin all have limitations which are exaggerated in children. This has led to the study of newer agents with improved pharmacologic properties such as bivalirudin, argatroban, and fondaparinux. Clinical trials are under way to assess several new oral anticoagulants that are in late phase studies or already licensed in adults. Based on the completed studies in children, several recommendations for the use of currently available agents (bivalirudin, argatroban, and fondaparinux) are suggested for clinical use today. Additional studies need to be conducted for the these agents, so that their use may be expanded in selected indications. New regulatory requirements are leading to a number of studies in the newer anticoagulants that are yet to be licensed in adults for treatment of venous thromboembolism. Pediatric thrombosis is entering a fruitful era of research in anticoagulation management, which is sure to lead to significant changes in how children are treated in the next 10 years.