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

Refractory Kawasaki Disease With a Giant Aneurysm Successfully Treated With Infliximab and Enoxaparin: A Case Report

Kawasaki disease (KD) is the most common vasculitis in children, and can result in the development of coronary artery aneurysms (CAAs) if not properly managed. While intravenous immunoglobulin (IVIG) and aspirin are standard first-line treatments, refractory KD may develop, increasing the risk of coronary complications. Herein, we report the case of a young girl with KD who initially responded to IVIG, but later developed a giant CAA, despite additional treatments. Infliximab stabilized her condition, and one year later, the CAA remained stable without thrombus formation. This case demonstrates that clinical appearance, particularly fever, may not fully reflect the patient's condition, as fever can subside immediately after treatment, but may relapse days later, underscoring the need for vigilant monitoring.

Anticoagulation in Pediatric Patients

The use of antithrombotic agents is increasing in infants, children and adolescents. The more recent routine inclusion of children in FDA-monitored clinical trials has propelled the rapid accumulation of safety and efficacy data on these agents in pediatric patients. Antithrombotic agents in current use include indirect or antithrombin-dependent anticoagulants, intravenous direct thrombin inhibitors, direct oral anticoagulants (DOACs) targeting thrombin or factor Xa, antiplatelet agents and thrombolytic therapies. Each class of antithrombotic agent has distinct mechanisms of action, clearance routes, half-lives, safety and dosing. Anticoagulant efficacy is dependent upon the specific clinical indication and stability of the pediatric patient. Duration of anticoagulant course is also dependent upon the clinical indication as well as rate of thrombus resolution. This manuscript reviews the mechanism of action, route of administration, route of clearance and plasma half-life for the antithrombotic agents in current use in children. Use of anticoagulation in the context of thrombolytic therapy is discussed.

The impact of child-specific characteristics on warfarin dosing requirements

Background

The influence of child characteristics on warfarin dosing has been reported; however, there is no consensus on the nature and extent of this effect.

Objectives

To investigate the impacts of the demographic and clinical characteristics of children on the warfarin dose required to achieve a therapeutic international normalization ratio (INR).

Methods

This retrospective cohort study included children aged 3 months to 14 years old who were prescribed warfarin for 3 months or longer with a "stable INR." The primary outcome was the total daily dose (TDD) and total weekly dose of warfarin required to achieve a therapeutic INR target.

Results

We included 127 patients with a mean age of 7.7 ± 3.7 years and a median weight of 22 (IQR, 16-33) kg. Of the sample, 55 patients (43.3%) required a TDD of ≤0.1 mg/kg. The TDD for children younger than 5 years, 5 to 10 years, and older than 10 years were 0.14 ± 0.06 mg/kg, 0.12 ± 0.05 mg/kg, and 0.096 ± 0.04 mg/kg, respectively (P = .002). Overweight and obese children required a smaller TDD than normal-weight children: 0.09 ± 0.05 vs 0.13 ± 0.05 mg/kg (P = .004), which was similar for underweight children. A lower body surface area (<0.5 m2) required a higher dose. All the other variables did not affect warfarin doses. The incidence of a subtherapeutic or supratherapeutic INR was independent of demographic or clinical variables.

Conclusion

The study confirmed that the patient demographics affect the daily warfarin dose required to achieve the INR target. However, they do not have any predictive value for the incidence of out-of-range-INR.

Efficacy and Safety of Direct Oral Anticoagulants in Pediatric Venous Thromboembolism: A Systematic Review and Meta-Analysis

OBJECTIVES

To assess the efficacy and safety of direct oral anticoagulants (DOACs) in comparison to standard-of-care (SOC) anticoagulants in the management and prophylaxis of thromboembolic events in pediatric populations.

METHODS

A comprehensive search of electronic databases was conducted to identify relevant studies published between January 1, 2015, and December 18, 2022. A meta-analysis was undertaken to evaluate the effect of DOACs on clinically significant endpoints, employing trial-level data with harmonized endpoint definitions. The primary outcome was venous thromboembolism (VTE). Odds ratios (ORs) with 95% confidence intervals (CIs) were calculated. The study was registered with INPLASY (2022120065).

RESULTS

Three studies encompassing 934 subjects were included. The incidence of VTE was reduced in patients administered DOACs compared to those on SOC anticoagulants (OR 0.41 [95% CI 0.19-0.93], I² = 0%, P = 0.03). No significant differences were observed between the DOAC and SOC groups in all-cause mortality (OR 0.50 [95% CI 0.07-3.59], I² = 0%, P = 0.35) or serious adverse events (OR 0.75 [95% CI 0.50-1.12], I² = 0%, P = 0.16). The risk of major bleeding (OR 0.50 [95% CI 0.13-1.87], I² = 44%, P = 0.30) and clinically relevant non-major bleeding (OR 1.23 [95% CI 0.50-3.00], I² = 0%, P = 0.65) exhibited no significant differences between the groups.

CONCLUSIONS

DOACs are associated with a reduced risk of VTE in pediatric patients without increasing the risk of bleeding, all-cause mortality, or serious adverse events when compared to SOC anticoagulants. DOACs may be an alternative for the treatment and prevention of thromboembolic events in the pediatrics.

Risk factors for serious adverse events related to vitamin K antagonists in children with congenital or acquired heart disease: a prospective cohort study

OBJECTIVES

To assess the occurrence of thrombosis and major bleeding in children with congenital or acquired heart disease (CAHD) treated with VKA and to identify risk factors for these serious adverse events (SAE).

STUDY DESIGN

All children enrolled in our VKA dedicated educational program between 2008 and 2022 were prospectively included. The time in therapeutic range (TTR) was calculated to evaluate the stability of anticoagulation. Statistical analysis included Cox proportional hazard models.

RESULTS

We included 405 patients. Median follow-up was 18.7 (9.3-49.4) months. The median TTR was 83.1 % (74.4 %-95.3 %). No deaths occurred because of bleeding or thrombotic events. The incidences of thrombotic and major bleeding events were 0.9 % (CI95 % [0.1-1.8]) and 2.3 % (CI95 % [0.9-3.8]) per patient year, respectively. At 1 and 5 years, 98.3 % (CI95 % [96.2 %-99.2 %]) and 88.7 % (CI95 % [81.9 % 93.1 %]) of patients were free of any SAE, respectively. Although the mechanical mitral valve (MMV) was associated to major bleeding events (HR = 3.1 CI95 % [1.2-8.2], p = 0.02) in univariate analysis, only recurrent minor bleeding events (HR = 4.3 CI95 % [1.6-11.7], p < 0.01) and global TTR under 70 % (HR = 4.7 CI95 % [1.5-15.1], p < 0.01) were independent risk factors in multivariable analysis. In multivariable analysis, giant coronary aneurysms after Kawasaki disease (HR = 7.8 [1.9-32.0], p = 0.005) was the only risk factor for thrombotic events.

CONCLUSION

Overall, VKA therapy appears to be safe in children with CAHD. Suboptimal TTR, regardless of the indication for VKA initiation, was associated with bleeding events.

Guiding warfarin self-management in children: development of a warfarin nomogram

Background

Warfarin therapy in children is impacted by many variables. To support the implementation of a self-management program within a pediatric anticoagulation service, a pediatric-specific warfarin nomogram was needed. A literature review revealed no published pediatric nomograms; therefore, a nomogram was developed drawing upon an evidence-based "Warfarin Information for Clinicians" hospital guideline.

Objectives

This study aimed to evaluate the suitability of a pediatric warfarin nomogram.

Methods

A retrospective audit of electronic medical records compared the dosing and international normalized ratio (INR) retest decisions made by hematology clinicians to the dosing and retesting recommended by a new warfarin nomogram at a pediatric hospital. Children (aged 6 months-18 years) receiving warfarin therapy for >6 months were included. Data were collected between September 2019 and February 2020. Descriptive data analysis was performed. The study was approved by the hospital's Human Research Ethics Committee.

Results

Warfarin dosing and INR retest decisions for 39 children were included, equating to 521 INRs. The nomogram matched 81.4% of clinicians dosing decisions and 30% of INR retest decisions. Moreover, 59% of the clinician-recommended retest dates were earlier than the nomogram recommendation. In the INR 2.0-3.0 group, 84.4% of dosing decisions and 72% of retest decisions matched the nomogram.

Conclusions

These results suggest that this pediatric nomogram is a suitable tool for warfarin dosing, as recommended warfarin doses matched the majority of clinicians' decisions. Modification may be needed to nomogram recommendations for the time to retest. This nomogram can be used to support warfarin self-management and may assist clinicians and patients or families in making evidence-based dosing decisions.

The effect of COVID-19 vaccination on anticoagulation stability in adolescents and young adults using vitamin K antagonists

INTRODUCTION

The European Medicine Agency has authorized COVID-19 vaccination in adolescents and young adults (AYAs) from 12 years onwards. In elderly vitamin K antagonist (VKA) users, COVID-19 vaccination has been associated with an increased risk of supra- and subtherapeutic INRs. Whether this association is also observed in AYAs using VKA is unknown. Our aim was to describe the stability of anticoagulation after COVID-19 vaccination in AYA VKA users.

MATERIALS AND METHODS

A case-crossover study was performed in a cohort of AYAs (12-30 years) using VKAs. The most recent INR results before vaccination, the reference period, were compared with the most recent INR after the first and, if applicable, second vaccination. Several sensitivity analyses were performed in which we restricted our analysis to stable patients and patients without interacting events.

RESULTS

101 AYAs were included, with a median age [IQR] of 25 [7] years, of whom 51.5 % were male and 68.3 % used acenocoumarol. We observed a decrease of 20.8 % in INRs within range after the first vaccination, due to an increase of 16.8 % in supratherapeutic INRs. These results were verified in our sensitivity analyses. No differences were observed after the second vaccination compared to before and after the first vaccination. Complications after vaccination occurred less often than before vaccination (9.0 vs 3.0 bleedings) and were non-severe.

CONCLUSIONS

the stability of anticoagulation after COVID-19 vaccination was decreased in AYA VKA users. However, the decrease might not be clinically relevant as no increase of complications nor significant dose adjustments were observed.

Evaluation of a Video-Based Education Intervention for Parents of Children Undergoing Fontan Surgery: A Cluster Randomized Controlled Trial

Background

Fontan surgery is performed at 2-4 years of age and is the third planned surgical intervention for children with a univentricular heart. Major challenges for children and parents after Fontan include (a) psychological distress, (b) prolonged pleural drainage, and (c) the need for postoperative anticoagulation. The aim of this study was to evaluate a pre-Fontan video-based intervention for parents to address these challenges.

Methods

This study is a single-centre mixed-methods cluster randomized controlled trial. The intervention consisted of 3 brief whiteboard videos offered online from preadmission clinic to 1 month postoperatively. The parent's State Trait Anxiety Inventory score and the child's Post Hospital Behaviour Questionnaire score were measured 1 week and 1 month postoperatively. Semistructured interviews were conducted to obtain parental feedback on the videos.

Results

We enrolled 26 children (13 female patients; 16 intervention group) and 1 parent per child. Mean State Trait Anxiety Inventory scores were similar between groups at both 1 week (52.8 vs 55.5, P = 0.25) and 1 month postoperatively (50.9 vs 53.9, P = 0.25). Post Hospital Behaviour Questionnaire scores were in the maladaptive range but did not differ between groups. Parents agreed or strongly agreed that the videos were helpful but should be provided earlier in the preoperative process. The main value of the videos was recognized as being a method for standardizing information provided to parents.

Conclusions

A video-based education intervention did not impact State Trait Anxiety Inventory or Post Hospital Behaviour Questionnaire scores. However, the majority of parents agreed that the videos were helpful.

A regional anticoagulation program improves safety and outcomes for both children and adults

BACKGROUND

Evidence-based anticoagulation programs usually serve a local, adult patient population. Here we report outcomes for a regional combined pediatric-adult program.

AIMS

The aims of this study were: (1) Compare the pre- vs. post-implementation quality of therapy (% time in therapeutic range (%TTR) and compliance). (2) Assess anticoagulant-relevant outcomes (bleeding and thrombotic complications).

METHODS

Data were collected for the years 2014-2019. Rosendaal linear interpolation was used to calculate %TTR. Bleeding complications were categorized using ISTH-SSC standard nomenclature and new thrombotic events were reviewed.

RESULTS

The patients were divided into a long-term warfarin group (N = 308), 80.2% of whom had cardiac-related therapeutic indications (median age 24y), and a second group (N = 114) comprised of short-term and non-warfarin long-term anticoagulation (median age 16y). Median %TTR for those on long-term warfarin was 78.9%. The incidence of major and clinically relevant non-major bleeding events was 1.65 and 2.43 /100 person-years of warfarin use, respectively. Thromboembolism (TE) incidence was 0.78/100 patient-years of warfarin use. Neither bleeding nor thrombosis was associated with %TTR (p = 0.48). Anticoagulant indication was the only variable associated with bleeding risk (p = 0.005). The second group had no on-therapy TE events but 7.9% experienced bleeding. Complete data were available for a randomly sampled pre-program warfarin group (N = 26). Median %TTR improved from 17.5 to 87% pre- vs. post-implementation. Similarly, compliance (defined as ≥ 1 INR/month) improved by 34.3%.

CONCLUSIONS

In conclusion, this program significantly improved and sustained %TTR and compliance. The lack of association between bleeding and thrombosis events and %TTR may be related to the high median %TTR (> 70%) achieved by this approach.

Cerebral Sinovenous Thrombosis in Infants and Children: A Practical Approach to Management

Cerebral sinovenous thrombosis (CSVT) is a rare, yet potentially devastating disorder, associated with acute complications and long-term neurologic sequelae. Consensus-based international pediatric CSVT treatment guidelines emphasize early clinical-radiologic recognition and prompt consideration for anticoagulation therapy. However, lack of clinical trials has precluded evidence-based patient selection, anticoagulant choice, optimal monitoring parameters and treatment duration. Consequently, uncertainties and controversies persist regarding anticoagulation practices in pediatric CSVT. This review focuses on commonly encountered issues that continue to pose questions and raise debates regarding anticoagulation therapy among pediatric neurologists and hematologists.

Anticoagulant Effects of Dabigatran on Coagulation Laboratory Parameters in Pediatric Patients: Combined Data from Five Pediatric Clinical Trials

Background  Dabigatran etexilate, a direct oral thrombin inhibitor, is approved to treat venous thromboembolism (VTE) in both adults and children.

Objectives  This population analysis characterized relationships between dabigatran total plasma concentrations and coagulation laboratory parameters (activated partial thromboplastin time [aPTT]; diluted thrombin time [dTT]; ecarin clotting time [ECT]).

Methods  Data from three phase 2a and one single-arm and one randomized, comparative phase 2b/3 pediatric studies (measurements: aPTT 2,925 [ N  = 358]; dTT 2,348 [ N  = 324]; ECT 2,929 [ N  = 357]) were compared with adult data (5,740 aPTT, 3,472 dTT, 3,817 ECT measurements; N  = 1,978). Population models were fitted using nonlinear mixed-effects modeling. Covariates (e.g., sex, age) were assessed on baseline and drug-effect parameters, using a stepwise covariate model-building procedure.

Results  Overall, relationships between dabigatran, aPTT, dTT, and ECT were similar in children and adults. For children aged <6 months, a higher proportion of baseline samples were outside or close to the upper aPTT and ECT adult ranges. No age-related differences were detected for dTT. With increasing dabigatran concentration, aPTT rose nonlinearly (half the maximum effect at 368 ng/mL dabigatran) while dTT and ECT increased linearly (0.37 and 0.73% change per ng/mL dabigatran, respectively). Mean baseline aPTT (45 vs. 36 seconds) and ECT (40 vs. 36 seconds) were slightly increased for those aged <6 months versus older children.

Conclusion  The similar relationships of laboratory parameters observed across pediatric age groups suggests that developmental changes in the hemostatic system may have little effect on response to dabigatran.

A Narrative Review of Postoperative Anticoagulation Therapy for Congenital Cardiac Disease

Congenital heart disease encompasses a range of cardiac birth defects. Some defects require early and complex surgical intervention and post-operative thromboprophylaxis primarily for valve, conduit, and shunt patency. Antiplatelet and anticoagulant management strategies vary considerably and may or may not align with recognized consensus practice guidelines. In addition, newer anticoagulant agents are being increasingly used in children, but these medications are not addressed in most consensus statements.

This narrative review evaluated the literature from 2011 through 2021 on the topic of postoperative thromboprophylaxis after congenital heart disease operations. The search was focused on the descriptions and results of pediatric studies for replacement and/or repair of heart valves, shunts, conduits, and other congenital heart disease operations. Wide variability in practice exists and, as was true a decade ago, few randomized controlled trials have been conducted. Aspirin, warfarin, and perioperative heparin remain the most commonly used agents with varying dosing, duration, and monitoring strategies, making comparisons difficult. Only recently have data on direct oral anticoagulants been published in children, suggesting evolving paradigms of care. Our findings highlight the need for more research to strengthen the evidence for standardized thromboprophylaxis strategies.

Anticoagulation in Pediatric Patients

Special aspects of anticoagulation in children include the different epidemiology of thrombosis, developmental changes in the coagulation system, age-dependent pharmacokinetics of anticoagulants, risk of bleeding, and practical hurdles to anticoagulation. The classical anticoagulants so far used in children have several limitations, resulting in the need for regular monitoring. The pharmacological properties of direct oral anticoagulants (DOACs) and the special challenges of anticoagulation in children make the DOACs particularly attractive for children. All DOACs have pediatric development programs, targeting various indications for prevention and treatment of thrombosis. Child-appropriate formulations have been developed, age-specific dosing information generated, and safety and efficacy evaluated in ongoing phase 3 trials. Rivaroxaban and dabigatran have already been authorized for children for treatment of acute venous thrombosis and for extended secondary prevention. Their safety and efficacy have been demonstrated comparable to that of standard-of-care anticoagulants, without need for monitoring. Further studies are ongoing, which are expected to lead to pediatric authorizations of DOACs for primary venous thromboembolic event prevention in some high-risk settings. More real-life data will be necessary from postmarketing studies and registries to complement the evidence base for DOAC use in children, particularly in the youngest age groups and special disease populations.

Hemorrhagic transformation and stroke recurrence in children with cardiac disease receiving antithrombotic therapy for secondary stroke prevention

BACKGROUND

Antithrombotic therapy is currently recommended for stroke prevention in pediatric cardioembolic stroke where the recurrence risk is high; however, safety concerns remain. The primary objective of this study was to evaluate clinical and radiographic predictors of hemorrhagic transformation and stroke recurrence in children with cardiac disease to ascertain the safety and failure rates for secondary stroke prevention.

METHODS

This was a single-center, retrospective analysis of a prospectively enrolled cohort of children with radiologically confirmed cardioembolic stroke from January 2003 to December 2017 treated with institutional guidelines.

RESULTS

Eighty-two children met inclusion criteria (male 44 [54%]; neonates 23 [28%]; median age 0.43 years [0.08-4.23]). Hemorrhagic transformation occurred in 20 (24%) with the majority (75% of 20) being petechial and asymptomatic. One death (1%) was reported from hemorrhagic transformation. Four children (5%) had major extracranial hemorrhage. Most (95%) received antithrombic therapy, with anticoagulation being favored (82%). Greater stroke volume was associated with hemorrhagic transformation using the pediatric Alberta Stroke Program Early CT Score (6.1 ± 3.3 vs. 3.5 ± 2.3; p = .006). Stroke recurred in 11 (13%) children at a median 32 days (5.5-93) from the index event and the majority (90%) were on treatment at the time of recurrence. Children with univentricular physiology were less likely to have hemorrhagic transformation (RR 0.31; 95% CI 0.09-0.96, p = .04); however, they had higher rates of recurrent stroke before final palliative repair.

CONCLUSIONS

In spite of the 24% hemorrhagic transformation rate, antithrombotic therapy has a positive risk-balance in certain cardioembolic stroke subgroups, particularly in those with single-ventricle physiology, when accounting for stroke volume.

Deciphering Genetic Variants of Warfarin Metabolism in Children With Ventricular Assist Devices

Warfarin is prescribed in patients with ventricular assist devices (VADs). Dosage depends on several factors including the underlying genotype. These include polymorphisms of genes encoding cytochrome P450 enzymes, the main ones being CYP2C9, VKORC1, and CYP4F2. The objectives of this study were to evaluate the prevalence of CY2CP9 1*2*3*, VKORC1, and CYP4F2 in children with VADs and the time to reach the target international normalized ratio. We performed a retrospective/prospective study in children with VADs. We recorded polymorphisms, disease, type of VAD, ethnicity, age, gender, height, weight, INR values, bleeding, and thromboembolic episodes. Informed consent was obtained. We enrolled 34 children (19 male, 15 female), with a median age of 2 years (range 0.3-17 years) and median weight of 6.9Kg. The Berlin Heart was the most commonly implanted VAD (22/34; 64%), and the most common diagnosis was dilated cardiomyopathy. Statistical analysis confirmed a significant partial correlation with VKORC1 CC (p = 0.019). The CYP2C9*2 CT genotype showed a late rise in target INR values (p = 0.06), while the CYP2C9*2 CC showed a tendency toward an early INR rise (p = 0.024). We provide new information on the contribution of the warfarin polymorphisms in children with VAD implantation. Pharmacogenomic dosing for children using warfarin has the potential to improve clinical care in VAD patients. Patients with the CYP2C9*2 CT genotype may need more time or higher doses to reach target INR, while clinicians may need to be aware of the potential for a rapid rise in INR in patients with the CYP2C9*2 CC genotype.

Transcatheter mechanical manipulation of obstructed prosthetic mitral valve in an infant

Prosthetic valve thrombosis is a serious complication of prosthetic heart valves that typically requires either surgical intervention or systemic thrombolysis. In patients with contraindications to both treatment modalities, options can be limited. We describe an alternative approach to managing prosthetic valve thrombosis in an infant presenting in extremis with pulmonary haemorrhage. Using transoesophageal echocardiography and fluoroscopic guidance, we restored function to the infant's obstructed St. Jude prosthetic mitral valve through percutaneous transcatheter manipulation of the valve's leaflets.

Challenges and Opportunities in the Pharmacological Treatment of Acute Venous Thromboembolism in Children

Venous thromboembolism (VTE) is an important but historically under-recognized problem in pediatrics, with an incidence concentrated in hospitalized children. A number of specific VTE diseases with discrete triggers have been described, but the most common pediatric trigger is the presence of central venous access devices. VTE diseases, though heterogenous in etiology, are linked by the common therapeutic strategies shared by their management. Historically, the most commonly used drug therapies have been unfractionated heparin, low-molecular-weight heparins, and vitamin K antagonists, based on extrapolation from adult data rather than any specific pediatric trials. Although these widely used drugs appear safe and effective in expert hands, the historical lack of pediatric data is problematic in view of the recognized significant differences between children and adults with regards to hemostatic physiology, VTE etiology, and drug pharmacokinetics. The increasing adult usage of novel VTE pharmacotherapies such as direct oral anticoagulants (DOACs) has led to considerable interest in exploring the pediatric applications of these newer drugs. This review summarizes the advantages and disadvantages of existing VTE pharmacotherapies and outlines emerging novel pediatric VTE therapies, particularly DOACs, within the context of the current pediatric trial landscape.

Venous Thromboembolism in Children: From Diagnosis to Management

Venous thromboembolism (VTE) in children is a rare occurrence, although in recent decades we have seen an increase due to several factors, such as the rise in survival of subjects with chronic conditions, the use of catheters, and the increased sensitivity of diagnostic tools. Besides inherited thrombophilia, acquired conditions such as cardiovascular diseases, infections, chronic disorders, obesity and malignancy are also common risk factors for paediatric VTE. The treatment of paediatric VTE consists of the use of heparins and/or vitamin K antagonists to prevent dissemination, embolization, and secondary VTE. Randomized clinical trials of direct oral anticoagulants in paediatric VTE are ongoing, with the aim to improve the compliance and the care of patients. We reviewed the physiological and pathological mechanisms underlying paediatric thrombosis and updated the current diagnosis and treatment options.

Evaluation of dosing and safety outcomes of low-dose prophylactic warfarin in children after cardiothoracic surgery

PURPOSE

Prophylactic warfarin with an International Normalized Ratio (INR) goal of 1.5 to 2.0 is one antithrombotic therapy utilized in children after cardiothoracic surgery (CTS); published sources suggest a dose of 0.1 mg/kg per day to achieve this goal. However, few studies have evaluated dosing in this population. The purpose of this study was to evaluate dosing and safety outcomes in children receiving warfarin after CTS.

METHODS

A descriptive, retrospective review was conducted to evaluate warfarin dosing and INR outcomes in patients 18 years of age or younger who underwent CTS and received prophylactic warfarin with an INR goal of 1.5 to 2.0 from January 2014 through December 2018. The primary objective was to determine the median initial warfarin dose. Secondary objectives included identifying the percentage of documented INR values that were outside the therapeutic range, the percentage of patients with therapeutic INRs at discharge, and the 30-day readmission rate.

RESULTS

Twenty-six patients were included in the review. The median initial warfarin dosage was 0.07 mg/kg/d (interquartile range [IQR], 0.05-0.10 mg/kg/d). Of the total of 177 INR values collected during the entire study period, 67 (37.9%) were therapeutic, 64 (36.2%) were subtherapeutic, and 46 (26.0%) were supratherapeutic. Eighteen patients (69.2%) had at least 1 supratherapeutic INR at any point during the study period, most frequently on days 2 through 4 of therapy. At discharge, 11 patients (42.3%) had therapeutic INRs. Four patients (15.4%) were readmitted within 30 days, with bleeding documented in 2 patients during their readmission.

CONCLUSION

The majority of patients received an initial warfarin dose less than that specified in published recommendations but still had a supratherapeutic INR at least once during the study period. When initiating warfarin after CTS, a dosage of <0.1 mg/kg per day and frequent monitoring may be needed to achieve an INR goal of 1.5 to 2.0.

Comparing Two Methods of Tablet Manipulation to Adjust the Warfarin Dose in Paediatric Care

Tablets containing prescribed doses are not always available, and this is of particular importance in paediatric care where suitable age-appropriate formulations are generally lacking. To obtain a child-adjusted dose, tablets are manipulated in several ways; e.g., they may be dispersed in water before a fraction is extracted, or they may be split before the resulting fragment is dispersed. In this study, the accuracy attained through these manipulation methods was investigated for two generic tablets containing the anticoagulant warfarin. Tablets were dispersed in water (10 mL) before a fraction (10%) was withdrawn, alternatively tablets were split in half or quarter fragments before the fragments were dispersed in water. To investigate the contribution of variability from the different steps in the manipulation processes, the amount of warfarin recovered from the various dispersions was determined, as was the accuracy of the splitting. A validated UHPLC-method was used for quantitative determination of warfarin. Splitting of the tablets could result in deviation >30% from the ideal, theoretical weight. The amount of drug substance extracted as a fraction from the dispersed tablets deviated no more than 10% from the intended amount. To obtain the most accurate child-adjusted fraction dose of warfarin, the tablets investigated in this study should be dispersed and the desired proportion extracted. Practices that involve splitting tablets are likely to increase the variation, and should be avoided.

Treatment of venous thromboembolism in pediatric patients

Venous thromboembolism (VTE) is rare in healthy children, but is an increasing problem in children with underlying medical conditions. Pediatric VTE encompasses a highly heterogenous population, with variation in age, thrombosis location, and underlying medical comorbidities. Evidence from pediatric clinical trials to guide treatment of VTE is lacking so treatment is often extrapolated from adult trials and expert consensus opinion. Aspects unique to children include developmental hemostasis and the major role of central venous access devices. There is an absence of information regarding the optimal target levels of anticoagulation for neonates and infants and lack of suitable drug formulations. Anticoagulants, primarily low-molecular-weight heparin and warfarin, are used to treat children with symptomatic VTE. These drugs have significant limitations, including the need for subcutaneous injections and frequent monitoring. Randomized clinical trials of direct oral anticoagulants in pediatric VTE are ongoing, with results anticipated soon. These trials will provide new evidence and options for therapy that have the potential to improve care. International collaborative registries offer the ability to study outcomes of rare subgroups of pediatric VTE (eg, renal vein thrombosis), and will be important to ultimately guide therapy in a more disease-specific manner.

Should Cytochrome P450 Inducers be Used to Accelerate Clearance of Brodifacoum from Poisoned Patients?

A recent multi-state outbreak of life-threatening bleeding following inhalation of synthetic cannabinoids has been attributed to contamination with the long-acting anticoagulant rodenticide (LAAR) brodifacoum, a second-generation, highly potent, long-acting derivative of the commonly used blood thinner warfarin. While long-term treatment with high-dose vitamin K1 restores coagulation, it does not affect brodifacoum metabolism or clearance, and, consequently, brodifacoum remains in the human body for several months, thereby predisposing to risk of bleeding recurrence and development of coagulation-independent injury in extrahepatic tissues and fetuses. This has prompted the evaluation of pharmacological measures that accelerate brodifacoum clearance from poisoned patients. Since the induction of certain cytochrome P450 (CYP) enzymes accelerates warfarin metabolism, using CYP inducers, such as phenobarbital, to accelerate brodifacoum clearance seems plausible. However, unlike warfarin, brodifacoum does not undergo significant metabolism in the liver, nor have the effects of phenobarbital on vitamin K1 metabolism been previously determined. In addition, the safety of phenobarbital in brodifacoum-poisoned patients has not been established. Therefore, we propose that CYP inducers should not be used to accelerate the clearance of brodifacoum from poisoned patients, but that alternative approaches such as reducing enterohepatic recirculation of brodifacoum, or using lipid emulsions to scavenge brodifacoum throughout the body, be considered.

Pediatric Thrombotic Events: Incidence, Clinical Risk Factors and Outcome

OBJECTIVE

To study the incidence, clinical risk factors and outcome of thrombotic events in pediatric age group of 1 mo-12 y.

METHODS

This prospective observational study was conducted in a tertiary care institute from September 2015 through October 2017. Forty nine children with thrombosis from 1 mo-12 y were enrolled.

RESULTS

Out of 49 cases, 30 (61.2%) were due to venous thromboembolism (VTE) and 19 (38.8%) were of arterial thromboembolism (ATE). The cumulative average annual incidence for VTEs was found to be 38.2 (n = 30) and for ATEs it was found to be 24.2 (n = 19) per 10,000 hospital admissions over 2 y of study period. With total of 19 (38.7%), catheters were the leading cause of thrombosis followed by infection numbering to 10 cases (20.4%). Total 42.8% cases (n = 21) achieved complete resolution. Partial resolution was noted in 53.2% of cases (n = 26) and no resolution in 4% cases (n = 2). Total seven (14.3%) deaths were recorded during the study period.

CONCLUSIONS

The present study showed that thrombosis is an emerging problem in tertiary care setting adding to both mortality and morbidity in children. Central venous catheters followed by infection were the leading cause of thrombosis in this study.

Considerations for Implementing Precision Therapeutics for Children

Improving the utilization of pharmacologic agents in the pediatric population yields significant, perhaps life‐long, benefits. Genetic factors related to the disposition of a medication or an alteration at the target receptor site contributes to the observed variability of exposure and response between individuals. An additional source of this variability specific to the pediatric population is ontogeny, where age‐specific changes during development may require dose adjustments to obtain the same levels of drug exposure and response. With significant improvements in characterizing both the ontogeny and genetic contributions of drug metabolizing enzymes, the time is right to begin placing more emphasis on response rather than only the dose‐exposure relationship. The amount of drug target receptors and the relative affinity for binding at that target site may require different levels of systemic exposure to achieve a desired response. Concentration‐controlled studies can identify the needed exposure for a response at the drug target, the level of expression of the target site in an individual patient, and the tools required to individualize response. Although pediatrics represents a large spectrum of growth and development, developing tools to improve drug delivery for each individual patient across the spectrum of the ages treated by clinicians remains valuable.

Personalised Warfarin Dosing in Children Post-cardiac Surgery

Warfarin dosing is challenging due to a multitude of factors affecting its pharmacokinetics (PK) and pharmacodynamics (PD). A novel personalised dosing algorithm predicated on a warfarin PK/PD model and incorporating CYP2C9 and VKORC1 genotype information has been developed for children. The present prospective, observational study aimed to compare the model with conventional weight-based dosing. The study involved two groups of children post-cardiac surgery: Group 1 were warfarin naïve, in whom loading and maintenance doses were estimated using the model over a 6-month duration and compared to historical case-matched controls. Group 2 were already established on maintenance therapy and randomised into a crossover study comparing the model with conventional maintenance dosing, over a 12-month period. Five patients enrolled in Group 1. Compared to the control group, the median time to achieve the first therapeutic INR was longer (5 vs. 2 days), to stable anticoagulation was shorter (29.0 vs. 96.5 days), to over-anticoagulation was longer (15.0 vs. 4.0 days). In addition, median percentage of INRs within the target range (%ITR) and percentage of time in therapeutic range (%TTR) was higher; 70% versus 47.4% and 83.4% versus 62.3%, respectively. Group 2 included 26 patients. No significant differences in INR control were found between model and conventional dosing phases; mean %ITR was 68.82% versus 67.9% (p = 0.84) and mean %TTR was 85.47% versus 80.2% (p = 0.09), respectively. The results suggest model-based dosing can improve anticoagulation control, particularly when initiating and stabilising warfarin dosing. Larger studies are needed to confirm these findings.

Height, VKORC1 1173, and CYP2C9 Genotypes Determine Warfarin Dose for Pediatric Patients with Kawasaki Disease in Southwest China

Long-term oral warfarin is recommended in pediatric Kawasaki disease patients with large coronary artery aneurysms; however, heterogeneity is considerable. This study aimed to determine variables affecting warfarin dosage in Kawasaki disease. The enrolled individuals (194 children) were divided into four groups: (1) Cases with severe coronary artery lesions (CAL) of IV to V degrees or thrombogenesis treated with oral warfarin were assigned to Group A; (2) Group B, CAL of I degrees; (3) Group C, CAL of II and III degrees cases with small or medium-sized CAL not treated with warfarin; (4) Group D, normal children without Kawasaki disease. The relevant genotypes of CYP2C9, VKORC1 (1173, - 1639, and 3730), and CYP4F2 were assessed. There were no statistically significant differences in CYP2C9, VKORC1, and CYP4F2 mutation frequencies among the 4 groups. In the 44 Group A patients, demographic features, clinical characteristics, and genotypes were recorded, and their associations with warfarin dose variability were assessed. Multivariate linear regression analysis revealed that height, VKORC1 1173, and CYP2C9 accounted for 61.2%, 7.9%, and 4.3% of dosing variability, respectively. Conclusions: Patient height is the main factor determining warfarin dosage, while genotype effects on warfarin dosage vary among studies. New formula should be defined using data obtained from children in cases with demonstrated efficacy.

Management of thrombosis in children and neonates: practical use of anticoagulants in children

Venous thrombosis (VTE) in children and neonates presents numerous management challenges. Although increasing in frequency, VTE in children and neonates is still uncommon compared with adults. The epidemiology of VTE is vastly different in neonates vs children vs adolescents vs adults. In reality, pediatric thrombosis should be viewed as a multitude of rare diseases (eg, renal vein thrombosis, spontaneous thrombosis, catheter-related thrombosis, cerebral sinovenous thrombosis), all requiring different approaches to diagnosis and with different short- and long-term consequences, but linked by the use of common therapeutic agents. Further, children have fundamentally different physiology in terms of blood flow, developmental hemostasis, and, likely, endothelial function. The American Society of Hematology 2017 Guidelines for Management of Venous Thromboembolism: Treatment of Pediatric VTE provides up-to-date evidence-based guidelines related to treatment. Therefore, this article will focus on the practical use of therapeutic agents in the management of pediatric VTE, especially unfractionated heparin, low-molecular-weight heparin, and oral vitamin K antagonists, as the most common anticoagulants used in children. Direct oral anticoagulants (DOACs) remain in clinical trials in children and should not be used outside of formal trials for the foreseeable future.

Weight and the vitamin K expoxide reductase 1 genotype primarily contribute to the warfarin dosing in pediatric patients with Kawasaki disease

INTRODUCTION

Warfarin therapy is recommended in children with giant coronary artery aneurysms (GCAAs) after Kawasaki disease (KD). Large individual variability makes it difficult to predict the warfarin dose. Polymorphisms in the vitamin K expoxide reductase 1 (VKORC1) and cytochrome P4502C9 (CYP2C9) genes have been reported to influence the warfarin dose. We investigated the effects of the VKORC1 and CYP2C9 genotypes on the warfarin dose in pediatric patients with giant CAAs after KD. We attempted to create a dosing algorithm.

MATERIALS AND METHODS

The clinical and genetic data of patients were documented. VKORC1 (rs 9923231) and CYP2C9 *3 (rs 1057910) were genotyped using TaqMan real-time polymerase chain reaction. A linear regression analysis was performed to evaluate the contribution of clinical and genetic factors to the warfarin maintenance dose.

RESULTS

Forty-seven patients were enrolled. Patients with the CT or CC genotype of VKORC1 had a relatively higher warfarin dose than did those with the TT genotype (p < 0.05). Three patients with CYP2C9*1/*3 had a lower warfarin dose than did those with the wild CYP2C9*1/*1 genotype, but the difference did not reach significance (p > 0.05). Weight and the VKORC1 genotype predominantly contributed to the warfarin dose, with 33.0% and 11.2% of variability, respectively. The observed warfarin dose was correlated with the predicted dose based on the algorithm used in our study (r = 0.45, p < 0.01).

CONCLUSIONS

Weight and the VKORC1 genotype primarily determined the warfarin dose in Chinese pediatric patients with KD. Further studies are warranted to verify the findings of our study.

[Thromboembolic disease in pediatric oncology]

The survival rate of children with cancer is now close to 80 %, as a result of continuous improvement in diagnostic and treatment procedures. Prevention and treatment of treatment-associated complications is now a major challenge. Thromboembolic venous disease, due to multifactorial pathogenesis, is a frequent complication (up to 40 % asymptomatic thrombosis in children with cancer), responsible for significant morbidity. Predominantly in children with acute lymphoblastic leukemia, lymphoma, or sarcoma, thromboembolic disease justifies primary prophylaxis in certain populations at risk, whether genetic or environmental. The curative treatment, well codified, is based on the administration of low-molecular-weight heparin. In the absence of robust pediatric prospective studies, this article proposes a concise decision tree summarizing the preventive and curative strategy.

Incidence and Management of Thrombotic and Thromboembolic Complications Following the Superior Cavopulmonary Anastomosis Procedure: A Literature Review

The objective of this literature review was to estimate the incidence of thrombosis and thromboembolism associated with the superior cavopulmonary anastomosis (SCPA) procedure and its variants and to examine current thromboprophylaxis regimens utilized. MEDLINE and EMBASE were searched from inception to August 2017 for all prospective and retrospective cohort studies explicitly reporting incidence of thrombosis, thromboembolism, or shunt occlusion in neonates, infants, and children undergoing 1 or more variants of the SCPA procedure. End points included thrombotic events and thromboembolic events (strokes and pulmonary embolisms) as primary outcomes, and overall mortality as a secondary outcome, at the last available follow-up time point. Of 1303 unique references identified, 13 cohort studies were deemed eligible. Reported incidence of thrombosis and thromboembolic events ranged from 0% to 28.0% and from 0% to 12.5%, respectively. Reported incidence of major bleeding events ranged from 0% to 2.9%. Reported overall mortality ranged from 2.5% to 50.5% across studies. Thromboprophylaxis protocols varied across institutions and studies, most commonly involving unfractionated heparin (UFH), warfarin, enoxaparin, acetylsalicylic acid (ASA), or combinations of ASA and warfarin, ASA and low-molecular-weight heparin (LMWH), UFH and LMWH, and UFH and ASA; several studies did not specify a protocol. Due to substantial variability in reported event rates, no clear correlation was identified between prophylaxis protocols and postoperative thrombotic complications. Despite guidance recommending postoperative UFH as standard practice, thromboprophylaxis protocols varied across institutions and studies. More robust trials evaluating different thromboprophylaxis regimens for the management of these patients are warranted.

Duration of anticoagulant therapy in pediatric venous thromboembolism: Current approaches and updates from randomized controlled trials

INTRODUCTION

Compared with the incidence of venous thromboembolism in the adult population, pediatric VTE is rare. Yet, recent data suggest that the incidence of VTE in children is increasing, and little is known about the optimal duration of anticoagulation in pediatrics. Areas covered: This review summarizes current evidence-based adult recommendations and associated clinical trials from which current guidelines on the duration of anticoagulation in children have been extrapolated. It also discusses pediatric expert consensus-based guidelines and current pediatric clinical trials on duration of therapy in pediatric VTE. Expert commentary: The vast majority of pediatric VTE are provoked, and evidence on duration of anticoagulation for pediatric VTE is highly limited, but suggests that a maximum duration of 3 months is reasonable for most patients with provoked VTE, whereas longer duration is likely appropriate for unprovoked VTE. Whether shorter duration than 3 months is optimal for pediatric provoked VTE is as yet unclear. Results from the multinational randomized controlled trial studying the duration of anticoagulant therapy for provoked VTE in patients <21 years old (Kids-DOTT) will be critical to inform the future standard of care in pediatric VTE treatment.

UNUSUAL WARFARIN DOSE TO ACHIEVE THERAPEUTIC INR IN A 4-MONTH OLD CHILD: NON-GENETICS RISK FACTORS ARE STILL A CHALLENGE

Objective:

To report a case of a 4-month old girl that required 0.7 mg/kg/day (5 mg) of warfarin and discuss relevant risk factors for requiring higher doses.

Case Description:

In November 2015, a 5 kg female infant (36-week preterm) was admitted to the hospital due to status epilepticus and fever. Diazepam, phenytoin and ceftriaxone were prescribed. Cerebrospinal fluid contained 7 leukocytes, 150 mg/dL proteins, 1 mg/dL glucose and gram positive cocci were observed. Cranial tomography suggested hypodense signs in the cerebellum, right temporal lobe and left basal nuclei, which was consistent with pneumococcal meningitis-induced infectious vasculitis. She required low molecular weight heparin and warfarin for post-encephalitis thrombosis. About 10 days were required to achieve therapeutic INR, and warfarin was adjusted five times since the initial prescription.

Comments:

The risk factors for higher warfarin doses were age and enteral tube feeding. Phenobarbital and prednisone might also have contributed with one of the highest warfarin dose ever reported. Despite current importance given to genetics testing, clinicians should attempt to identify common contributing factors for prolonged non-therapeutic INR, to minimize the risk of coagulation, and to reduce costs of hospital stay and laboratory exams.

Anticoagulation Therapies in Children

Venous thromboembolism is occurring with increasing frequency in children resulting in the more widespread use of anticoagulation in pediatrics. Antithrombotic drugs in children can be divided into the standard and alternative agents. This review discusses standard and alternative anticoagulants. Because standard anticoagulants have significant limitations, including variable pharmacokinetics, issues with therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects, it is expected that the use of alternative anticoagulants will increase over time. With their improved properties and recent prospective clinical trial data, the current and future use of these agents will likely slowly replace of the standard anticoagulants.

Safety, tolerability and clinical pharmacology of dabigatran etexilate in adolescents

Venous thromboembolism (VTE) incidence is increasing among children owing to many factors, including improved diagnosis of VTE. There is a need for alternative treatment options. Our objective was to investigate the safety, pharmacokinetics (PK) and pharmacodynamics (PD) of dabigatran etexilate in adolescents with VTE. Adolescents aged 12 to <18 years (n = 9) who successfully completed planned treatment for primary VTE were administered dabigatran etexilate twice daily for three days; initially 1.71 (± 10%) mg/kg (80% of a 150 mg/70 kg twice daily adult dose), followed by 2.14 (± 10%) mg/kg (target adult dose adjusted for patient’s weight), if there were no safety concerns. No bleeding events, deaths or drug-related serious adverse events (AEs) were reported; three treatment-emergent AEs, all gastrointestinal-related, occurred in two patients. In these adolescent patients with normal renal function, presumed steady-state trough plasma concentrations of dabigatran were low (geometric mean dosenormalised total dabigatran plasma concentration: 0.493 ng/ml/mg at 72 hours). Total dabigatran concentrations were well predicted by the RE-LY® population PK model (94% of trough concentrations were within the 80% prediction interval). The relationship between total dabigatran plasma concentration, diluted thrombin time and ecarin clotting time (ECT) was linear; the relationship with activated partial thromboplastin time (aPTT) was non-linear. Adult population PK/PD models predicted the adolescent concentration–ECT and –aPTT relationships well. In conclusion, dabigatran etexilate was generally well tolerated, except for occurrence of dyspepsia in two patients, over the three-day treatment period. The dabigatran PK/PD relationship observed in adolescent patients was similar to that in adult patients.

Institution where work was performed: Main clinical study site: Children’s Hospital of Eastern Ontario, Ottawa, Ontario, Canada.

This study is registered at ClinicalTrials.gov (NCT00844415).

Home point-of-care international normalised ratio monitoring sustained by a non-selective educational program in children

Adverse events related to vitamin K antagonist (VKA) therapy might be reduced by point-of-care international normalised ratio (POC INR) monitoring supported by an education program (EP). Our aim was to evaluate the efficacy of a non-selective VKA paediatric EP (regardless of the social, economic, educational or linguistic levels) by analysing the time spent in the therapeutic range (TTR), VKA adverse events and compliance to treatment, and INR control prescriptions. The EP was modified from the pediatric EP previously described but improved by a specifically devised child-focused game. One hundred four consecutive children (median age 8 years) receiving VKA were included in a standardised E P. Patients were in self-testing, and dose adjustments were made by a single physician for three tolerance ranges according to the underlying disease: [2.5–4], [1.8–3.2], and [1.5–2.5]. The median follow-up was 481 days [70–1,001]. The overall TTR was 81.4% [36–100]. The TTR were 74%, 85.6% and 89% for the ranges [2.5–4], [1.8–3.2], and [1.5–2.5], respectively. These results were sustainable during the study period. Only one serious VKA adverse event was recorded. The median number of POC INR tests was 2.5 [1.6–5.7] INR per patient and month. Patients/families performed POC INR when requested in 86.9% of the cases. More than 90% of the families found the EP supportive and wished to follow a long-term reinforcement program. In conclusion, this non-selective child-focused EP for VKA therapy, strongly supported by our dedicated game, is useful in maintaining efficacy, safety and compliance to anticoagulation and its monitoring.

USE OF WARFARIN IN PEDIATRICS: CLINICAL AND PHARMACOLOGICAL CHARACTERISTICS

Objective:

To describe how children respond to oral anticoagulation with warfarin, verifying the influence of age, clinical condition, route of administration of warfarin and use of total parenteral nutrition (TPN), as well as to describe risk factors for the occurrence of thrombotic events (TE) in childhood.

Methods:

A retrospective descriptive study including all patients ≤18 years old for whom warfarin was prescribed in a university hospital. Patients were divided according to clinical condition, age, route of medication administration and use of TPN. Data was collected from the patients’ medical records and the analysis considered the risk factors for TE already described in the literature, the time and the dose required in order to reach the first International Normalized Ratio (INR) in the target and the adverse events in this period. After reaching the INR, the maintenance of anticoagulation was verified by the prescribed dose and INR tests.

Results:

Twenty-nine patients were included in the study. The major risk factor for TE was the use of a central venous catheter in 89.6% of the patients. Patients with short bowel syndrome and total parenteral nutrition required significantly higher doses (p≤0.05) to achieve and maintain the INR in the target. Patients ≤1 year old needed longer periods and required an increased dose of anticoagulation and maintenance than older patients. The mean number of INR examinations below the target was 48.2% in the groups studied.

Conclusions:

The observed complexity of anticoagulant therapy reinforces the need to develop protocols that guide clinical practice.

Anticoagulation in children: Making the most of little patients and little evidence

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 standard agents (heparin, low molecular weight heparin, and vitamin K antagonists) and alternative agents (argatroban, bivalirudin, and fondaparinux). This review will compare and contrast the standard and alternative anticoagulants and suggest situations in which it may be appropriate to use argatroban, bivalirudin, and fondaparinux. Clearly, the standard anticoagulants all have significant shortcomings including variable pharmacokinetics, issues with therapeutic drug monitoring, frequency of administration, efficacy, and adverse effects. The alternative anticoagulants have properties which overcome these shortcomings and prospective clinical trial data are presented supporting the current and future use of these agents in place of the standard anticoagulants.

Personalised dosing of medicines for children

Objectives

Doses for most drugs are determined from population-level information, resulting in a standard ?one-size-fits-all’ dose range for all individuals. This review explores how doses can be personalised through the use of the individuals’ pharmacokinetic (PK)-pharmacodynamic (PD) profile, its particular application in children, and therapy areas where such approaches have made inroads.

Key findings

The Bayesian forecasting approach, based on population PK/PD models that account for variability in exposure and response, is a potent method for personalising drug therapy. Its potential utility is even greater in young children where additional sources of variability are observed such as maturation of eliminating enzymes and organs. The benefits of personalised dosing are most easily demonstrated for drugs with narrow therapeutic ranges such as antibiotics and cytotoxics and limited studies have shown improved outcomes. However, for a variety of reasons the approach has struggled to make more widespread impact at the bedside: complex dosing algorithms, high level of technical skills required, lack of randomised controlled clinical trials and the need for regulatory approval.

Summary

Personalised dosing will be a necessary corollary of the new precision medicine initiative. However, it faces a number of challenges that need to be overcome before such an approach to dosing in children becomes the norm.

Incidence and Management of Thrombotic and Thromboembolic Complications Following the Norwood Procedure: A Systematic Review

Background:

The stage 1 Norwood procedure and its variants represent the first step of palliation for hypoplastic left heart syndrome. Although appropriate postoperative thromboprophylaxis is integral, significant variance remains across institutional practices. The purpose of this systematic review is to estimate the incidence of thrombosis and thromboembolism following the Norwood or modified Blalock-Taussig shunt procedure and examine current thromboprophylaxis regimens.

Methods:

Ovid MEDLINE and Embase were searched from January 2000 to June 2016 for primary studies explicitly reporting incidence of thrombosis, thromboembolism (strokes and pulmonary embolisms), or shunt occlusion in neonates, infants, and children undergoing the Norwood procedure or any variant. All-cause mortality was a secondary outcome of interest.

Results:

Of 887 identified articles, 15 cohort studies were deemed eligible, the majority including modified Blalock-Taussig shunt patients. Reported incidence of thrombosis ranged from 0% to 40%; thromboembolic events were rarely reported. Overall mortality ranged from 4.5% to 31.3% across studies. Although most studies involved the long-term acetylsalicylic acid use, thromboprophylaxis strategies varied across studies. Due to substantial variability in event rates, no correlation was identified with thrombotic complications.

Discussion:

Clinical practice guidelines recommend that patients receive intraoperative unfractionated heparin therapy and either aspirin or no antithrombotic therapy postoperatively. Our findings suggest a substantial risk of thrombosis and thromboembolism and demonstrate substantial variation in thromboprophylaxis practices.

Conclusion:

Although postoperative thromboprophylaxis seems optimal, it remains controversial whether the long-term aspirin use is most effective. Our findings highlight the lack of a gold-standard thromboprophylaxis strategy and emphasize the need for more consistency.

Immunizations in Children Requiring Warfarin Therapy

Children with conditions requiring chronic warfarin therapy have increased. The importance of receiving immunizations in this population is magnified due to potential weakness in their immune response. There is concern about immunizing on therapeutic anticoagulation due to risk of hematomas and the influence of vaccine on warfarin metabolism. This study evaluated the influence of vaccines on warfarin effect as measured by the International Normalized Ratio and the clinically relevant hematomas or bruising postimmunization. There were no clinically relevant negative outcomes postimmunizations. This study demonstrates that immunizations may be safely administered to children receiving therapeutic warfarin therapy.

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.