Abstract:503
The optimal dosing strategy of low molecular weight heparins (LMWH) for the treatment of antenatal venous thromboembolism (VTE) is not known. The physiological changes associated with pregnancy alter the pharmacokinetic (PK) profile of LMWH, and this has led to controversy and subsequent variation in practice, when pregnant women are managed with LMWH for VTE [Voke et al., 2009]. The perceived impact of these PK changes has led to the Royal College of Obstetrics and Gynaecologists (RCOG) rec… Show more
“…We also demonstrated a marked variability in AXA concentrations within individual patients, which we believe is related to changing PK during pregnancy. The changes in AXA concentrations support Casele et al ’s findings that clearance decreases in late pregnancy . Only 49.6% of all AXA concentrations in the MV population were therapeutic, indicating the difficulties in dosing this special population and the potential risks of both thrombosis and bleeding.…”
Section: Discussionsupporting
confidence: 80%
“…The changes in AXA concentrations support Casele et al's findings that clearance decreases in late pregnancy. 16,24 Only 49.6% of all AXA concentrations in the MV population were therapeutic, indicating the difficulties in dosing this special population and the potential risks of both thrombosis and bleeding. The wide variability in management suggests that a protocol formed in collaboration with medical, obstetric, pharmacy and clinical pharmacology teams is warranted, ideally at a national level to ensure consistency across hospital sites.…”
Background
Therapeutic anticoagulation with enoxaparin in pregnancy is complex due to varying pharmacokinetics and the increasing prevalence of obesity. There is limited evidence to support current dosing and monitoring strategies of enoxaparin in this population.
Aim
To describe the current practice in therapeutic anticoagulation in the pregnant population at a tertiary institution.
Methods
A retrospective study of pregnant women on therapeutic enoxaparin between January 2007 and December 2011.
Results
Forty‐four pregnant women requiring therapeutic anticoagulation were identified and divided into two groups, monitored with anti‐factor Xa (AXA) concentrations and unmonitored. Fifty‐five percent of monitored women were initiated on the recommended 1 mg/kg twice a day (bd) enoxaparin dose‐strategy. Eighty‐two percent of women were monitored; however, there was variability regarding the timing, frequency and subsequent dose adjustments from monitoring. Overall, as pregnancies progressed, there was both increasing dose adjustments and increasing frequency of monitoring. Fourteen women had a BMI over 30 kg/m2, and 13 of these women were monitored. Nine monitored obese women required doses less than 1 mg/kg/bd to maintain a therapeutic AXA level. Management appeared to be individualised. There were small numbers of toxicity events.
Conclusion
Variation exists in dosing and monitoring practices for therapeutic enoxaparin in the pregnant population. Dosing obese patients using 1 mg/kg twice daily can lead to toxic AXA concentrations, and dose reductions are required to maintain a therapeutic range. A larger prospective study reviewing dose, AXA concentrations and outcome data is necessary to make dosing recommendations in this group.
“…We also demonstrated a marked variability in AXA concentrations within individual patients, which we believe is related to changing PK during pregnancy. The changes in AXA concentrations support Casele et al ’s findings that clearance decreases in late pregnancy . Only 49.6% of all AXA concentrations in the MV population were therapeutic, indicating the difficulties in dosing this special population and the potential risks of both thrombosis and bleeding.…”
Section: Discussionsupporting
confidence: 80%
“…The changes in AXA concentrations support Casele et al's findings that clearance decreases in late pregnancy. 16,24 Only 49.6% of all AXA concentrations in the MV population were therapeutic, indicating the difficulties in dosing this special population and the potential risks of both thrombosis and bleeding. The wide variability in management suggests that a protocol formed in collaboration with medical, obstetric, pharmacy and clinical pharmacology teams is warranted, ideally at a national level to ensure consistency across hospital sites.…”
Background
Therapeutic anticoagulation with enoxaparin in pregnancy is complex due to varying pharmacokinetics and the increasing prevalence of obesity. There is limited evidence to support current dosing and monitoring strategies of enoxaparin in this population.
Aim
To describe the current practice in therapeutic anticoagulation in the pregnant population at a tertiary institution.
Methods
A retrospective study of pregnant women on therapeutic enoxaparin between January 2007 and December 2011.
Results
Forty‐four pregnant women requiring therapeutic anticoagulation were identified and divided into two groups, monitored with anti‐factor Xa (AXA) concentrations and unmonitored. Fifty‐five percent of monitored women were initiated on the recommended 1 mg/kg twice a day (bd) enoxaparin dose‐strategy. Eighty‐two percent of women were monitored; however, there was variability regarding the timing, frequency and subsequent dose adjustments from monitoring. Overall, as pregnancies progressed, there was both increasing dose adjustments and increasing frequency of monitoring. Fourteen women had a BMI over 30 kg/m2, and 13 of these women were monitored. Nine monitored obese women required doses less than 1 mg/kg/bd to maintain a therapeutic AXA level. Management appeared to be individualised. There were small numbers of toxicity events.
Conclusion
Variation exists in dosing and monitoring practices for therapeutic enoxaparin in the pregnant population. Dosing obese patients using 1 mg/kg twice daily can lead to toxic AXA concentrations, and dose reductions are required to maintain a therapeutic range. A larger prospective study reviewing dose, AXA concentrations and outcome data is necessary to make dosing recommendations in this group.
“…For example, population PK analysis has previously provided compelling evidence that enoxaparin could be administered once daily during the antenatal period for the treatment of VTE. 27…”
Section: Population Pharmacokinetic Modellingmentioning
Background
Emerging safety and efficacy data for rivaroxaban suggest traditional therapy and rivaroxaban are comparable in the morbidly obese. However, real‐world data that indicate pharmacokinetic (PK) parameters are comparable at the extremes of body size are lacking. The International Society of Thrombosis and Haemostasis Scientific and Standardisation Committee (ISTH SSC) suggests avoiding the use of direct oral anticoagulants (DOACs) in patients weighing >120 kg or with a body mass index >40 kg/m2 and gives no recommendation on the use of DOACs in those <50 kg.
Objectives
To generate a population PK model to understand the influence of bodyweight on rivaroxaban exposure from clinical practice data.
Method
Rivaroxaban plasma concentrations and patient characteristics were collated between 2013 and 2018 at King's College Hospital anticoagulation clinic. A population PK model was developed using a nonlinear mixed effects approach and then used to simulate rivaroxaban concentrations at the extremes of bodyweight.
Results
A robust population PK model derived from 913 patients weighing between 39 kg and 172 kg was developed. The model included data from n = 86 >120 kg, n = 74 BMI >40 kg/m2, and n = 30 <50 kg. A one‐compartment model with between‐subject variability on clearance and a proportional error model best described the data. Creatinine clearance calculated by Cockcroft‐Gault, with lean bodyweight as the weight descriptor in this equation, was the most significant covariate influencing rivaroxaban exposure.
Conclusions
Our work demonstrates rivaroxaban can be used at extremes of bodyweight provided renal function is satisfactory. We recommend that the ISTH SSC revises the current guidance with respect to rivaroxaban at extremes of body size.
“…At 24 hours, the anti-Xa level was 0.29 IU/ml which was above the locally accepted level for haemostasis (0.20 IU/ml). Recent antenatal pharmacokinetic data with LMWH supports the case observation of increased trough anti-Xa activity with pregnancy that may lead to modification of future international guidelines 10 .…”
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