Population pharmacodynamic model for low molecular weight heparin nadroparin in morbidly obese and non-obese patients using anti-Xa levels as endpoint

Is the current therapeutic dosage of nadroparin adequate for neonates and infants under 8 months with thromboembolic disease? a population pharmacokinetic study from a national children's medical center

Objectives: Nadroparin, a low-molecular-weight-heparin is commonly used off-label in neonates and infants for thromboembolic events prevention. However, the recommended dosing regimen often fails to achieve therapeutic target ranges. This study aimed to develop a population pharmacokinetic (PK) model of nadroparin to determine an appropriate dosing regimen for neonates and infants less than 8 months. Methods: A retrospective chart review was conducted on patients treated with nadroparin at Children's Hospital of Fudan University between July 2021 and December 2023. A population PK model was developed using anti-Xa levels, and its predictive performance was evaluated internally. Monte Carlo simulations were performed to design an initial dosing schedule targeting anti-Xa levels between 0.5 and 1 IU/mL. Results: A total of 40 neonates and infants aged less than 8 months with gestational age ranging from 25 to 41 weeks treated with nadroparin were enrolled in the study for analysis. A one-compartment PK model with first order absorption and elimination was adequately fitted to the data. Creatinine clearance was identified as a significant factor contributing to inter-individual variability in clearance. The typical population parameter estimates of clearance, distribution volume and absorption rate in this population were 0.211 L/h, 1.55 L and 0.495 h-1, respectively. Our findings suggest that current therapeutic doses of nadroparin (150-200 IU/kg q12 h) may result in subtherapeutic exposure, thus higher doses might be required. Conclusion: The present study offers the first estimation of PK parameters for nadroparin in preterm or term neonates and infants less than 8 months utilizing the model. Our findings have potential implications for recommending initial personalized dosages, particularly among patient populations exhibiting similar characteristics.

The effect of renal impairment and obesity on anti-Xa peak and trough levels in patients receiving therapeutic doses of nadroparin: a comparison with control patients

PURPOSE

Anti-Xa peak level monitoring is recommended during LMWH treatment in renal impairment or obesity. The trough level has been proposed as marker for bleeding. We studied the influence of renal impairment and obesity on anti-Xa levels.

METHODS

Peak and trough levels were collected during therapeutic nadroparin treatment in patients with renal impairment, obese patients, and controls. 27 patients (n = 68 samples) were evaluated and combined with published data (n = 319 samples from 35 patients) using population pharmacokinetic (popPK) modelling.

RESULTS

Median peak level was 0.44 and 0.95 IU/mL in renal impairment with and without dose reduction and 0.60 and 0.43 IU/mL in obesity and controls, respectively. Trough levels were < 0.5 IU/mL in all patients with renal impairment with dose reduction and in 5/6 control patients. In the popPK model, total body weight and eGFR were covariates for clearance and lean body weight for distribution volume. Model-based evaluations demonstrated peak levels below the therapeutic window in controls and increased levels in renal impairment. Dose reductions resulted in a different effect on peak and trough levels. Obese patients (BMI up to 32 kg/m2) had similar levels upon weight-based dosing.

CONCLUSION

In renal impairment, anti-Xa peak levels after dose reduction are comparable to those in controls. Weight-based dosing is suitable for obese patients. Aiming for peak levels between 0.6 and 1.0 IU/mL in these patients would result in overexposure compared to controls. Considering the association of trough levels and bleeding risk and our findings, trough monitoring seems to be a suitable parameter to identify nadroparin accumulation.

Population Pharmacokinetics and Probability of Target Attainment Analysis of Nadroparin in Different Stages of COVID-19

BACKGROUND AND OBJECTIVE

The risk of thrombotic complications in critical patients with COVID-19 remains extremely high, and multicenter trials failed to prove a survival benefit of escalated doses of low-molecular-weight heparins (nadroparin calcium) in this group. The aim of this study was to develop a pharmacokinetic model of nadroparin according to different stages of COVID-19 severity.

METHODS

Blood samples were obtained from 43 patients with COVID-19 who received nadroparin and were treated with conventional oxygen therapy, mechanical ventilation, and extracorporeal membrane oxygenation. We recorded clinical, biochemical, and hemodynamic variables during 72 h of treatment. The analyzed data comprised 782 serum nadroparin concentrations and 219 anti-Xa levels. We conducted population nonlinear mixed-effects modeling (NONMEM) and performed Monte Carlo simulations of the probability of target attainment for reaching 0.2-0.5 IU/mL anti-Xa levels in study groups.

RESULTS

We successfully developed a one-compartment model to describe the population pharmacokinetics of nadroparin in different stages of COVID-19. The absorption rate constant of nadroparin was 3.8 and 3.2 times lower, concentration clearance was 2.22 and 2.93 times higher, and anti-Xa clearance was 0.87 and 1.1 times higher in mechanically ventilated patients and the extracorporeal membrane oxygenation group compared with patients treated with conventional oxygen, respectively. The newly developed model indicated that 5.900 IU of nadroparin given subcutaneously twice daily in the mechanically ventilated patients led to a similar probability of target attainment of 90% as 5.900 IU of subcutaneous nadroparin given once daily in the group supplemented with conventional oxygen.

CONCLUSIONS

Different nadroparin dosing is required for patients undergoing mechanical ventilation and extracorporeal membrane oxygenation to achieve the same targets as those for non-critically ill patients.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov identifier no. NCT05621915.

The right time to measure anti-Xa activity in critical illness: pharmacokinetics of therapeutic dose nadroparin

Background

Peak anti-Xa activity of low-molecular-weight heparin nadroparin is measured 3 to 5 hours after subcutaneous injection. In critically ill patients, physiological changes and medical therapies may result in peak activities before or after this interval, possibly impacting dosing.

Objectives

The primary objective was to determine the percentage of critically ill patients with adequately estimated peak activities drawn 3 to 5 hours after subcutaneous administration of a therapeutic dose of nadroparin. Adequate was defined as a peak activity of ≥80% of the actual peak anti-Xa activity. If ≥80% of patients had adequately estimated peak activities in the 3- to 5-hour interval, measurement in this interval was regarded as acceptable. The secondary objective was to determine the pharmacokinetic profile of nadroparin.

Methods

In this single-center, prospective study, we evaluated anti-Xa activities in patients admitted to a general intensive care unit. After ≥4 equal doses of nadroparin, anti-Xa activity was measured according to a 12- to 24-hour sampling scheme.

Results

In 25 patients, anti-Xa activities drawn between 3 and 5 hours after administration ranged 80% to 100% of the actual peak activity. Compared to the threshold level of an adequate estimation in at least 20 patients (≥80%), measuring anti-Xa activities in the 3- to 5-hour interval is an acceptable method (1-tailed binomial test; P < .02). We found a large interindividual variability for nadroparin exposure (mean ± SD area-under-the-curve_0-12h, 10.3 ± 4.8 IU·h/mL) and delayed elimination (t_1/2 range, 4.0-120.9 hours) despite adequate renal function.

Conclusion

In critically ill patients, measuring anti-Xa activity in a 3- to 5-hour interval after subcutaneous injection of therapeutic nadroparin is an acceptable method to estimate the actual peak anti-Xa activity.

Drug pharmacokinetics in the obese population: challenging common assumptions on predictors of obesity-related parameter changes

INTRODUCTION

Obesity is associated with many physiological changes. We review available evidence regarding five commonly accepted assumptions to a priori predict the impact of obesity on drug pharmacokinetics (PK).

AREAS COVERED

The investigated assumptions are: 1) lean body weight is the preferred descriptor of clearance and dose adjustments; 2) volume of distribution increases for lipophilic, but not for hydrophilic drugs; 3) CYP-3A4 activity is suppressed and UGT activity is increased, implying decreased and increased dose requirements for substrates of these enzyme systems, respectively; 4) glomerular filtration rate is enhanced, necessitating higher doses for drugs cleared through glomerular filtration; 5) drug dosing information from obese adults can be extrapolated to obese adolescents.

EXPERT OPINION

Available literature contradicts, or at least limits the generalizability, of all five assumptions. Clinical studies should focus on quantifying the impact of duration and severity of obesity on drug PK in adults and adolescents, and also include oral bioavailability and pharmacodynamics in these studies. Physiologically-based PK approaches can be used to predict PK changes for individual drugs, but can also be used to define in general terms based on patient characteristics and drug properties, when certain assumptions can or cannot be expected to be systematically accurate.

Optimising the Nadroparin Dose for Thromboprophylaxis During Hemodialysis by Developing a Population Pharmacodynamic Model Using Anti-Xa Levels

INTRODUCTION

The optimal nadroparin dose in patients undergoing hemodialysis is difficult to determine in clinical practice. Anti-Xa levels ≥ 0.4 IU/mL and < 2.0 IU/mL are suggested to prevent thrombus formation within the extracorporeal circuit whilst minimizing bleeding risk. We aimed to characterize the variability in the association between dose and anti-Xa levels, identify patient and dialysis characteristics that explained this variability, and optimize nadroparin dosing based on the identified characteristics.

METHODS

Anti-Xa samples were collected in patients who received intravenous nadroparin as thromboprophylaxis during routine dialysis sessions. A population pharmacodynamic model was developed using non-linear mixed-effects modelling. The percentage of patients ≥ 0.4 IU/mL (efficacy) and < 2.0 IU/mL (safety) was simulated for different doses, patient and dialysis characteristics.

RESULTS

Patients (n = 137) were predominantly receiving standard hemodialysis (84.7% vs. hemodiafiltration 15.3%) and had a mean bodyweight of 76.3 kg (± 16.9). Lean body mass (LBM), mode of dialysis, and dialyzer partially explained between-subject variability in anti-Xa levels. Patients on hemodiafiltration and those receiving hemodialysis with a high LBM (≥ 80 kg) had a low probability (< 29%) of anti-Xa levels ≥ 0.4 IU/mL during the entire dialysis session. All patients, except hemodialysis patients with a low LBM (< 50 kg), had a high probability (> 70%) of peak anti-Xa levels < 2.0 IU/mL.

CONCLUSION

Mainly patients receiving hemodiafiltration and those receiving hemodialysis with a high LBM can benefit from a higher nadroparin dose than currently used in clinical practice, while having anti-Xa levels < 2.0 IU/mL.

Influence of Morbid Obesity on the Pharmacokinetics of Morphine, Morphine-3-Glucuronide, and Morphine-6-Glucuronide

Introduction

Obesity is associated with many pathophysiological changes that may result in altered drug metabolism. The aim of this study is to investigate the influence of obesity on the pharmacokinetics of morphine, morphine-3-glucuronide (M3G), and morphine-6-glucuronide (M6G) through a combined analysis in morbidly obese patients and non-obese healthy volunteers.

Methods

In this analysis, data from 20 morbidly obese patients [mean body mass index 49.9 kg/m² (range 37.6–78.6 kg/m²) and weight 151.3 kg (range 112–251.9 kg)] and 20 healthy volunteers [mean weight 70.6 kg (range 58–85 kg)] were included. Morbidly obese patients received 10 mg of intravenous (I.V.) morphine after gastric bypass surgery, with additional morphine I.V. doses as needed. Healthy volunteers received an I.V. bolus of morphine of 0.1 mg/kg followed by an infusion of 0.030 mg kg⁻¹ h⁻¹ for 1 h. Population pharmacokinetic modeling was performed using NONMEM 7.2.

Results

In morbidly obese patients, elimination clearance of M3G and M6G was decreased substantially compared with healthy volunteers (p < 0.001). Regarding glucuronidation, only a slight decrease in the formation of M6G and a delay in the formation of M3G was found (both p < 0.001). Obesity was also identified as a covariate for the peripheral volume of distribution of morphine (p < 0.001).

Conclusion

Metabolism of morphine is not altered in morbidly obese patients. However, decreased elimination of both M3G and M6G is evident, resulting in a substantial increase in exposure to these two metabolites. A rational explanation of this finding is that it results from alterations in membrane transporter function and/or expression in the liver.

ClinicalTrials.gov identifier: NCT01097148.

Electronic supplementary material

The online version of this article (doi:10.1007/s40262-017-0544-2) contains supplementary material, which is available to authorized users.

Obesity and drug pharmacology: a review of the influence of obesity on pharmacokinetic and pharmacodynamic parameters

INTRODUCTION

The rising prevalence of obesity confronts clinicians with dosing problems in the (extreme) overweight population. Obesity has a great impact on key organs that play a role in the pharmacokinetics (PK) and pharmacodynamics (PD) of drugs, however the ultimate impact of these changes on how to adapt the dose may not always be known. Areas covered: In this review, physiological changes associated with obesity are discussed. An overview is provided on the alterations in absorption, distribution, drug metabolism and clearance in (morbid) obesity focusing on general principles that can be extracted from pharmacokinetic studies. Also, relevant pharmacodynamic considerations in obesity are discussed. Expert opinion: Over the last two decades, increased knowledge is generated on PK and PD in obesity. Future research should focus on filling in the knowledge gaps that remain, especially in connecting obesity-related physiological changes with changes in PK and/or PD and vice versa. Ultimately, this knowledge can be used to develop physiologically based PK and PD models on the basis of quantitative systems pharmacology principles. Moreover, efforts should focus on thorough prospective evaluation of developed model-based doses with subsequent implementation of these dosing recommendations in clinical practice.

The Effect of Obesity on Anti-Xa Concentrations in Bariatric Patients

BACKGROUND

Morbidly obese patients are at increased risk to develop venous thromboembolism (VTE), especially after bariatric surgery. Adequate postoperative thrombosis prophylaxis is of utmost importance. It is assumed that morbidly obese patients need higher doses of low molecular weight heparin (LMWH) compared to normal-weight patients; however, current guidelines based on relative efficacy in obese populations are lacking.

OBJECTIVES

First, we will evaluate the relationship between body weight descriptors and anti-Xa activity prospectively. Second, we will determine the dose-linearity of LMWH in morbidly obese patients.

SETTING

This study was performed in a general hospital specialized in bariatric surgery.

METHODS

Patients were scheduled for a Roux-en-Y gastric bypass with a total bodyweight (TBW) of ≥ 140 kg. Patients (n = 50, 64% female) received a daily postoperative dose of 5700 IU of nadroparin for 4 weeks. Anti-Xa activity was determined 4 h after the last nadroparin administration. To determine the dose linearity, anti-Xa was determined following a preoperative dose of 2850 IU nadroparin in another 50 patients (52%).

RESULTS

TBW of the complete group was 148.5 ± 12.6 kg. Mean anti-Xa activity following 5700 IU nadroparin was 0.19 ± 0.07 IU/mL. Of all patients, 32% had anti-Xa levels below the prophylactic range. Anti-Xa activity inversely correlated with TBW (correlation coefficient - 0.410) and lean body weight (LBW; correlation coefficient - 0.447); 67% of patients with a LBW ≥ 80 kg had insufficient anti-Xa activity concentrations. No VTE events occurred.

CONCLUSIONS

In morbidly obese patients, a postoperative dose of 5700 IU of nadroparin resulted in subprophylactic exposure in a significant proportion of patients. Especially in patients with LBW ≥ 80 kg, a higher dose may potentially be required to reach adequate prophylactic anti-Xa levels.

Drug Dosing in Obese Children: Challenges and Evidence-Based Strategies

With the alarming increase of obesity in children, pediatricians are increasingly being confronted with difficult dosing decisions. Many drug labels do not provide specific dosing instructions for children who are obese. In this article, we describe the physiologic parameters altered by obesity and their influences on drug disposition and effect. We review the principles of allometry, and the key pharmacokinetic parameters that can be used to derive age appropriate dosing regimens. Last, we illustrate how appropriate weight descriptors can be selected, and how important PK parameters can be extrapolated for dosing in obese children when pediatric pharmacokinetic information is available.

The Use of Gene Ontology Term and KEGG Pathway Enrichment for Analysis of Drug Half-Life

A drug's biological half-life is defined as the time required for the human body to metabolize or eliminate 50% of the initial drug dosage. Correctly measuring the half-life of a given drug is helpful for the safe and accurate usage of the drug. In this study, we investigated which gene ontology (GO) terms and biological pathways were highly related to the determination of drug half-life. The investigated drugs, with known half-lives, were analyzed based on their enrichment scores for associated GO terms and KEGG pathways. These scores indicate which GO terms or KEGG pathways the drug targets. The feature selection method, minimum redundancy maximum relevance, was used to analyze these GO terms and KEGG pathways and to identify important GO terms and pathways, such as sodium-independent organic anion transmembrane transporter activity (GO:0015347), monoamine transmembrane transporter activity (GO:0008504), negative regulation of synaptic transmission (GO:0050805), neuroactive ligand-receptor interaction (hsa04080), serotonergic synapse (hsa04726), and linoleic acid metabolism (hsa00591), among others. This analysis confirmed our results and may show evidence for a new method in studying drug half-lives and building effective computational methods for the prediction of drug half-lives.

Best anaesthetic drug strategy for morbidly obese patients

PURPOSE OF REVIEW

The purpose of this review is to describe an evidence-based drug strategy applicable to any obese patient, rather than to present one standard 'ideal' anaesthetic drug combination. The ultimate choice of specific drugs in any given situation will depend upon clinician experience, patient specifics, and drug availability. The fundamental principle in anaesthesia for the obese patient is to use the shortest acting, least fat soluble agents to ensure rapid recovery to safe levels of alertness and mobility.

RECENT FINDINGS

No new drugs have been introduced over the past few years, but we have seen an introduction of enhanced recovery after surgery-based protocols into bariatric surgery. Our understanding of how obesity affects pharmacokinetics/dynamics of our drugs is improving, with new and better use of established drugs. Allometric scaling is being tested in the different pharmacokinetic/dynamic models used in target controlled infusion devices, with improved performance as a result. Obstructive sleep apnoea has a significant impact upon outcome and utilization of clinical resources, including critical care beds. If an improved drug dosing strategy will reduce this impact, then this would be a step forward.

SUMMARY

This review introduces newer findings to help us use anaesthetic and analgesic drugs more safely in the morbidly obese. However, there remain many areas of uncertainty with a lack of consensus on many issues.

Acute phase treatment of VTE: Anticoagulation, including non-vitamin K antagonist oral anticoagulants

The acute phase of venous thromboembolism (VTE) treatment focuses on the prompt and safe initiation of full-dose anticoagulation to decrease morbidity and mortality. Immediate management consists of resuscitation, supportive care, and thrombolysis for patients with haemodynamically significant pulmonary embolism (PE) or limb-threatening deep-vein thrombosis (DVT). Patients with contraindications to anticoagulants are considered for vena cava filters. Disposition for the acute treatment of VTE is then considered based on published risk scores and the patient's social status, as the first seven days carries the highest risk for VTE recurrence, extension and bleeding due to anticoagulation. Next, a review of: immediate and long-term bleeding risk, comorbidities (i. e. active cancer, renal failure, obesity, thrombophilia), medications, patient preference, VTE location and potential for pregnancy should be undertaken. This will help determine the most suitable anticoagulant for immediate treatment. The non-vitamin K antagonist oral anticoagulants (NOACs), including the factor Xa inhibitors apixaban, edoxaban and rivaroxaban as well as the direct-thrombin inhibitor dabigatran, are increasing the convenience of and options available for VTE treatment. Current options for immediate treatment include low-molecular-weight heparin (LMWH), unfractionated heparin (UFH), fondaparinux, apixaban, or rivaroxaban. LMWH or UFH may be continued as monotherapy or transitioned to treatment with a VKA, dabigatran or edoxaban. This review describes the upfront treatment of VTE and the evolving role of NOACs in the contemporary management of VTE.