Effect of Renal Function on the Pharmacokinetics of Enoxaparin and Consequences on Dose Adjustment

Current and emerging drug strategies for the prevention of venous thromboembolism in acutely ill medical inpatients

INTRODUCTION

Venous thromboembolism (VTE) is a common complication in patients hospitalized for acute medical illnesses. Therefore, medical inpatients require a careful VTE and bleeding risk assessment to drive optimal strategies for VTE prevention. Low molecular weight heparin and fondaparinux have long been used for inhospital prophylaxis for patients at increased risk of VTE. The selection of patients who require post-discharge prophylaxis, and the role of direct oral anticoagulants remain debated. New molecules currently under development may contribute to improve the risk benefit of VTE prevention in this setting.

AREAS COVERED

This text summarizes the evidence on approved treatments and on other drugs for the prevention of VTE in acutely ill medical patients. The main focus is on their pharmacological proprieties, clinical efficacy and safety, and the current license approved by the FDA (Food and Drug Administration) and EMA (European Medicines Agency), giving the readers a way to compare available drugs to date. The trials presented consider both inhospital and extended prophylaxis.

EXPERT OPINION

Thanks to the potentially favorable safety profile, factor XI inhibitors may play a role in the prevention of VTE in this setting. The expert opinion section discusses pharmacological properties, prophylaxis trials, and potential clinical applications of this novel class of drugs.

Anti-Xa Activity of Enoxaparin for Prevention of Venous Thromboembolism in Severe Nephrotic Syndrome-A Single Center Prospective Study

Severe nephrotic syndrome (NS) is associated with high risk of venous thromboembolic events (VTE), as well as presumably altered heparin pharmacokinetics and pharmacodynamics. Although prophylactic anticoagulation is recommended, the optimal dose is not established. The aim of the study was to test two co-primary hypotheses: of reduced enoxaparin effectiveness and of the need for dose-adjustment in NS. Forty two nephrotic patients with serum albumin ≤2.5 g/dL were alternately assigned to a standard fixed-dose of enoxaparin (NS-FD: 40 mg/day) or ideal body weight (IBW)-based adjusted-dose (NS-AD: 1 mg/kg/day). Twenty one matched non-proteinuric individuals (C-FD) also received fixed-dose. Co-primary outcomes were: the achievement of low- and high-VTE risk threshold of antifactor-Xa activity (anti-FXa) defined as 0.2 IU/mL and 0.3 IU/mL, respectively. Low-VTE-risk threshold was achieved less often in NS-FD than C-FD group (91 vs. 62%, p = 0.024), while the high-VTE-risk threshold more often in NS-AD than in NS-FD group (90 vs. 38%, p < 0.001). Two VTE were observed in NS during 12 months of follow-up (incidence: 5.88%/year). In both cases anti-FXa were 0.3 IU/mL implying the use of anti-FXa >0.3 IU/mL as a target for dose-adjustment logistic regression models. We determined the optimal dose/IBW cut-off value at 0.8 mg/kg and further developed bivariate model (termed the DoAT model) including dose/IBW and antithrombin activity that improved the diagnostic accuracy (AUC 0.85 ± 0.06 vs. AUC 0.75 ± 0.08). Enoxaparin efficacy is reduced in severe NS and the dose should be adjusted to ideal body weight to achieve target anti-FXa activity.

Tinzaparin Safety in Patients With Cancer and Renal Impairment: A Systematic Review

Low-molecular-weight heparins are approved for primary and secondary venous thromboembolism prevention. Tinzaparin is the low-molecular-weight heparin with the highest average molecular weight. The purpose of this systematic review is to provide an update regarding the safety profile of tinzaparin, prescribed either as a prophylactic or as a therapeutic regimen for venous thromboembolism in special populations, including cancer patients and patients with renal impairment. We identified prospective studies up to August 2020 reporting safety outcomes for cancer patients and patients with renal impairment on tinzaparin regimens. In patients with cancer major bleeding rates fluctuated between 0.8% and 7%. Patients on tinzaparin exhibited significantly lower rates of clinically relevant nonmajor bleeding events in comparison with those on vitamin K antagonists. Bioaccumulation of tinzaparin was not correlated with age, body weight or creatinine clearance. Periodic administration of either prophylactic or therapeutic doses of tinzaparin did not result in bioaccumulation, even in patients with severe renal impairment and creatinine clearance < 20 ml/min. Major bleeding rates for non-cancer patients with renal impairment on prophylactic tinzaparin regimens were 0%. Non-cancer patients with renal impairment on therapeutic tinzaparin regimens exhibited major bleeding in 0 to 3.4% of cases; major bleeding rates were higher for cancer patients with renal impairment on therapeutic tinzaparin regimens (4.3 to 10%). Tinzaparin can be used without dose adjustment in patients with severe renal impairment and creatinine clearance > 20 ml/min. Tinzaparin represents a safe choice for special populations at increased risk for thrombosis and bleeding.

Pharmacokinetics of Enoxaparin After Renal Transplantation in Pediatric Patients

Enoxaparin is commonly used in the prevention of renal allograft vascular thrombosis but off-label in children, and no consensus exists regarding the optimal dosing and dose adjustment. In this retrospective study, 444 anti-Xa levels were obtained from 30 pediatric renal transplant recipients in order to investigate enoxaparin population pharmacokinetics. The main results were (1) 25% of children achieved the target anti-Xa activity 36 hours after initiation of treatment, (2) anti-Xa time courses were best described by a 1-compartment open model with first-order absorption, (3) body weight but not renal function was the sole covariate influencing clearance and volume of distribution, and (4) large between-subject and between-occasion variabilities in anti-Xa activity were observed. However, creatinine-based estimated glomerular filtration rate in the first post-renal transplantation hours may not reliably reflect the actual renal function of the children. Based on the final population model, a Bayesian-based program was developed in order to estimate the individual pharmacokinetic parameters on a single anti-Xa measurement, allowing determination of the next enoxaparin dose that will quickly achieve an appropriate anti-Xa activity (targeting 0.3-0.5 IU/mL) and anticoagulation. Finally, these results should help standardize practices that remain to date largely heterogeneous in pediatric intensive care units.

Can we reliably predict the level of anticoagulation after enoxaparin injection in elderly patients with renal failure?

OBJECTIVES

The aim of this study was to evaluate the activity of anti-activated factor X (anti-Xa) in patients with different degrees of chronic renal failure (CRF), treated with therapeutic doses of low molecular weight heparin.

DESIGN

This prospective study evaluated the effect of age, renal function, BMI, gender, in determining the efficacy and safety of treatment with enoxaparin, evaluated by assessing the anti-Xa. The therapeutic anticoagulant range was set between 0.20 and 0.70 U/mL.

SETTING

Two hospital geriatric units.

PARTICIPANTS

98 patients (64 men, 34 women, mean age 82 years) with CRF, treated with enoxaparin at therapeutic dosage, for deep vein thrombosis or acute coronary syndrome.

MEASUREMENTS

Anti-Xa was assessed 4 h after the third administration of LMWH using Chromogenix test. Renal function was assessed by calculating creatinine clearance according to Cockcroft formula.

RESULTS

The dose of enoxaparin ranged between 53 and 200 U/kg; total 4000-16000 U/day. The mean anti-Xa was 0.41 U/mL (95% CI 0.36-0.45). Multiple regression analysis selected only the dose of enoxaparin, but not age, creatinine clearance, BMI, gender, as a predictor of anti-Xa serum levels. In seven patients anti-Xa was above the range but none of them received more than 150 U/Kg enoxaparin (100 U/kg if creatinine clearance <30 mL/min). Ten patients (eight men, two women) showed suboptimal levels of anti-Xa, regardless enoxaparin dose or creatinine clearance.

CONCLUSION

Enoxaparin dose reduction according to renal function decreases the risk of overdosing and potentially the risk of bleeding. The risk of under dosing seems less predictable; therefore, anti-Xa assay may be useful in severe clinical situations that require higher anticoagulant activity.

What do we learn from repeated population analyses?

Population analyses are performed on new and existing drugs. They play an important role in quantifying the time course of drug effects and provide a means of understanding the impact of variability between individuals on dosing requirements. For some drugs there have been several population analyses reported in the literature. It is important to understand how repeated population analyses can value add and what authors and readers can consider when reviewing such analyses. The purpose of this review is to explore what is learnt from repeated population analyses and provide an understanding of how the value-added nature of these analyses can be considered.

Pharmacodynamics assessment of Bemiparin after multiple prophylactic and single therapeutic doses in adult and elderly healthy volunteers and in subjects with varying degrees of renal impairment

INTRODUCTION

Aging and renal impairment may prolong the half-life and lead to accumulation of low molecular weight heparins. Correct dosing is critical to prevent bleeding or thrombosis.

MATERIALS AND METHODS

Open, parallel study. Healthy adult [n=13] and elderly (>65yrs) [n=12] volunteers; and subjects with mild (ClCr≥50 to ≤80mL/min, n=8), moderate (ClCr≥30 to <50mL/min, n=7), and severe (ClCr<30mL/min, n=8) renal impairment received four prophylactic doses (3,500IU/24h) and a single therapeutic dose (115IU/kg) of bemiparin with an interim washout period. Anti-FXa activity and the potential need for dose adjustment were evaluated.

RESULTS

There were statistically significant differences in the severe renal impairment group vs. adult volunteers in all anti-FXa related parameters, but no significant differences in any of the anti-FXa related parameters between the adult and the elderly. Anti-FXa simulations after 10 prophylactic doses predicted mean Amax=0.59IU/mL in subjects with severe renal impairment and 0.33-0.39IU/mL in the rest. Simulations in the severe renal impairment group with dose adjustment (2,500IU/24h) predicted all individual Amax<0.60IU/mL (mean Amax=0.42IU/ml). Simulations after 10 therapeutic doses predicted mean Amax=1.22IU/mL in severe renal impairment group and 0.89-0.98IU/mL in the rest. Simulations in the severe renal impairment group with 75% dose adjustment predicted individual Amax≤1.60IU/mL (mean Amax=0.91IU/mL).

CONCLUSIONS

No dose adjustments are required in elderly with preserved renal function. A dose adjustment of bemiparin is only advisable in patients with severe renal impairment when using prophylactic or therapeutic doses.

Non-therapeutic anti-Xa levels in medical patients receiving anticoagulant therapy with enoxaparin

INTRODUCTION

Anticoagulant activity of enoxaparin is not routinely monitored even when previous studies have shown a high pharmacological variability. The aim of this study is to determine the prevalence of non-therapeutic anti-Xa levels among medical patients using enoxaparin as anticoagulant therapy and to point out potential risk factors related to the risk of having a sub-therapeutic level.

MATERIALS AND METHODS

Anti-Xa levels were measured in a cohort of sixty patients with medical indication for enoxaparin. Patients were categorized according to anti-Xa levels as follows: suboptimal anticoagulation (<0.5 IU/ml), optimal anticoagulation (between 0.5 and 1.2 IU/ml) or overanticoagulated (>1.2 IU/ml). Demographic and clinical variables and the use of concomitant medications were described for each group. Univariate and multivariate analysis were performed to assess the relationship between sub-optimal anticoagulation and potential predictive variables. A linear regression analysis was done to assess the relationship between anti-Xa activity, age, weight, body mass index, administered dose/weight and creatinine clearance.

RESULTS

The mean anti-Xa activity was 0.71±0.32 UI/ml. Thirty one percent of patients had anti-Xa levels out of the therapeutic range, most of them (twenty-eight percent of total population) with a sub-therapeutic level. None of the variables were associated with the risk of a sub-therapeutic anti-Xa level.

CONCLUSION

Almost one third of patients receiving enoxaparin had anti-Xa levels out of the therapeutic range. We need more studies to determine the clinical relevance of these findings.

Interpreting population pharmacokinetic-pharmacodynamic analyses - a clinical viewpoint

The population analysis approach is an important tool for clinical pharmacology in aiding the dose individualization of medicines. However, due to their statistical complexity the clinical utility of population analyses is often overlooked. One of the key reasons to conduct a population analysis is to investigate the potential benefits of individualization of drug dosing based on patient characteristics (termed covariate identification). The purpose of this review is to provide a tool to interpret and extract information from publications that describe population analysis. The target audience is those readers who are aware of population analyses but have not conducted the technical aspects of an analysis themselves. Initially we introduce the general framework of population analysis and work through a simple example with visual plots. We then follow-up with specific details on how to interpret population analyses for the purpose of identifying covariates and how to interpret their likely importance for dose individualization.

Modelling the occurrence and severity of enoxaparin-induced bleeding and bruising events

AIMS

To develop a population pharmacokinetic-pharmacodynamic model to describe the occurrence and severity of bleeding or bruising as a function of enoxaparin exposure.

METHODS

Data were obtained from a randomized controlled trial (n = 118) that compared conventional dosing of enoxaparin (product label) with an individualized dosing regimen. Anti-Xa concentrations were sampled using a sparse design and the size, location and type of bruising and bleeding event, during enoxaparin therapy, were collected daily. A population pharmacokinetic-pharmacodynamic analysis was performed using nonlinear mixed effects techniques. The final model was used to explore how the probability of events in patients with obesity and/or renal impairment varied under differing dosing strategies.

RESULTS

Three hundred and forty-nine anti-Xa concentrations were available for analysis. A two-compartment first-order absorption and elimination model best fit the data, with lean body weight describing between-subject variability in clearance and central volume of distribution. A three-category proportional-odds model described the occurrence and severity of events as a function of both cumulative enoxaparin AUC (cAUC) and subject age. Simulations showed that individualized dosing decreased the probability of a bleeding or major bruising event when compared with conventional dosing, which was most noticeable in subjects with obesity and renal impairment.

CONCLUSIONS

The occurrence and severity of a bleeding or major bruising event to enoxaparin, administered for the treatment of a thromboembolic disease, can be described as a function of both cAUC and subject age. Individualized dosing of enoxaparin will reduce the probability of an event.

Pharmacokinetics and dosage adjustment in patients with renal dysfunction

INTRODUCTION

Chronic kidney disease is a common, progressive illness that is becoming a global public health problem. In patients with kidney dysfunction, the renal excretion of parent drug and/or its metabolites will be impaired, leading to their excessive accumulation in the body. In addition, the plasma protein binding of drugs may be significantly reduced, which in turn could influence the pharmacokinetic processes of distribution and elimination. The activity of several drug-metabolizing enzymes and drug transporters has been shown to be impaired in chronic renal failure. In patients with end-stage renal disease, dialysis techniques such as hemodialysis and continuous ambulatory peritoneal dialysis may remove drugs from the body, necessitating dosage adjustment.

METHODS

Inappropriate dosing in patients with renal dysfunction can cause toxicity or ineffective therapy. Therefore, the normal dosage regimen of a drug may have to be adjusted in a patient with renal dysfunction. Dosage adjustment is based on the remaining kidney function, most often estimated on the basis of the patient's glomerular filtration rate (GFR) estimated by the Cockroft-Gault formula. Net renal excretion of drug is a combination of three processes: glomerular filtration, tubular secretion and tubular reabsorption. Therefore, dosage adjustment based on GFR may not always be appropriate and a re-evaluation of markers of renal function may be required.

DISCUSSION

According to EMEA and FDA guidelines, a pharmacokinetic study should be carried out during the development phase of a new drug that is likely to be used in patients with renal dysfunction and whose pharmacokinetics are likely to be significantly altered in these patients. This study should be carried out in carefully selected subjects with varying degrees of renal dysfunction. In addition to this two-stage pharmacokinetic approach, a population PK/PD study in patients participating in phase II/phase III clinical trials can also be used to assess the impact of renal dysfunction on the drug's pharmacokinetics and pharmacodynamics.

CONCLUSION

In conclusion, renal dysfunction affects more that just the renal handling of drugs and/or active drug metabolites. Even when the dosage adjustment recommended for patients with renal dysfunction are carefully followed, adverse drug reactions remain common.

Study of bioaccumulation of dalteparin at a prophylactic dose in patients with various degrees of impaired renal function

BACKGROUND

Low-molecular-weight heparins (LMWH) have been shown to be effective and safe for prophylaxis of thromboembolic diseases. However, issues regarding safety and optimal use of LMWH arise in patients with renal insufficiency (RI).

OBJECTIVES

To compare pharmacokinetic data of dalteparin for up to 3 weeks in patients with various degrees of RI.

PATIENTS AND METHODS

Patients from general medical and surgical wards were included in this prospective cohort study and divided into three groups according to renal function: A=normal (GFR>or=60 mL min(-1)1.73 m(-2)), B=mild RI (GFR 30-59 mL min(-1)1.73 m(-2)), C=severe RI (GFR<30 mL min(-1)1.73 m(-2)). Dalteparin was injected s.c. once daily at a prophylactic dose. Peak anti-Xa activity levels (anti-Xa) were measured 4+/-1 h after injection on day 1 and every third day up to 3 weeks. Primary objectives were peak anti-Xa levels and adjusted anti-Xa levels, adjustment being carried out for dose and body weight.

RESULTS

A total of 42 patients could be analyzed during a median of 10 days (interquartile range IQR 4-13, range 1-20). In all groups, adjusted peak anti-Xa levels were not different on day 10 compared with day 1. No bioaccumulation>30% could be found up to day 10 even in patients with severe RI.

CONCLUSION

The use of dalteparin at a prophylactic dose was not associated with a bioaccumulation>30% even in patients with severe renal insufficiency during a median follow-up of 10 days (IQR 4-13, range 1-20).

Anti-factor Xa activity of enoxaparin administered at prophylactic dosage to patients over 75 years old

AIMS

Major bleeding complications with low-molecular-weight heparin (LMWH) treatment have been reported both in clinical studies and during postmarketing surveillance. Monitoring of antifactor Xa (anti-Xa) activities is therefore recommended in special populations often predisposed to renal impairment. The PROPHRE.75 study was conducted to estimate the distribution parameters of anti-Xa activity in the elderly.

METHODS

PROPHRE.75 was a prospective study of a cohort of consecutive patients aged >75 years and treated with 4000 IU of enoxaparin once daily for venous thromboembolism prophylaxis. Dosing history and measurements of anti-Xa activity in sparse samples were recorded throughout treatment. The covariates included weight, gender, age, renal function, medical history and concomitant medication. Population parameters and interindividual variability were estimated using NONMEM V software.

RESULTS

Anti-Xa activity was studied in 189 patients (mean age 82 +/- 5 years, 22% weighing <50 kg, 50% presenting renal impairment according to the Cockcroft and Gault formula). A first-order input two-compartment model best fitted the data. Clearance was significantly related to body weight and creatinine clearance based on the simplified Modification of Diet in Renal Disease formula, central volume being related to body weight. According to individual Bayesian estimations, 4% of patients presented with a peak anti-Xa activity >1.0 IU ml(-1), but this group did not include the sole patient experiencing a major bleed (0.53%).

CONCLUSIONS

Systematic monitoring of anti-Xa activity in elderly patients treated with enoxaparin at prophylactic doses does not seem to be necessary to prevent the occurrence of major bleeding.

Development of a dosage strategy in patients receiving enoxaparin by continuous intravenous infusion using modelling and simulation

AIM

To develop an appropriate dosing strategy for continuous intravenous infusions (CII) of enoxaparin by minimizing the percentage of steady-state anti-Xa concentration (C(ss)) outside the therapeutic range of 0.5-1.2 IU ml(-1).

METHODS

A nonlinear mixed effects model was developed with NONMEM for 48 adult patients who received CII of enoxaparin with infusion durations that ranged from 8 to 894 h at rates between 100 and 1600 IU h(-1). Three hundred and sixty-three anti-Xa concentration measurements were available from patients who received CII. These were combined with 309 anti-Xa concentrations from 35 patients who received subcutaneous enoxaparin. The effects of age, body size, height, sex, creatinine clearance (CrCL) and patient location [intensive care unit (ICU) or general medical unit] on pharmacokinetic (PK) parameters were evaluated. Monte Carlo simulations were used to (i) evaluate covariate effects on C(ss) and (ii) compare the impact of different infusion rates on predicted C(ss). The best dose was selected based on the highest probability that the C(ss) achieved would lie within the therapeutic range.

RESULTS

A two-compartment linear model with additive and proportional residual error for general medical unit patients and only a proportional error for patients in ICU provided the best description of the data. Both CrCL and weight were found to affect significantly clearance and volume of distribution of the central compartment, respectively. Simulations suggested that the best doses for patients in the ICU setting were 50 IU kg(-1) per 12 h (4.2 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). The best doses for patients in the general medical unit were 60 IU kg(-1) per 12 h (5.0 IU kg(-1) h(-1)) if CrCL < 30 ml min(-1); 70 IU kg(-1) per 12 h (5.8 IU kg(-1) h(-1)) if CrCL was 30-50 ml min(-1); and 100 IU kg(-1) per 12 h (8.3 IU kg(-1) h(-1)) if CrCL > 50 ml min(-1). These best doses were selected based on providing the lowest equal probability of either being above or below the therapeutic range and the highest probability that the C(ss) achieved would lie within the therapeutic range.

CONCLUSIONS

The dose of enoxaparin should be individualized to the patients' renal function and weight. There is some evidence to support slightly lower doses of CII enoxaparin in patients in the ICU setting.

Development of an Efficient Sampling Strategy to Predict Enoxaparin Pharmacokinetics in Stage 5 Chronic Kidney Disease

Patients with renal dysfunction are at greater risk for hemorrhagic events than patients with normal renal function. The objective of this study was to develop an efficient sampling strategy that optimally predicts anti-Xa activity exposure after enoxaparin administration in patients with chronic kidney disease to optimize enoxaparin therapy. The antifactor Xa activity data of 8 anuric patients who were administered 1 mg/kg enoxaparin immediately after hemodialysis were used for the development of the optimal sampling strategies. Maximum A Posteriori Bayesian (MAPB) priors were developed by pharmacokinetic analysis. The 2, 3, and 4 D-optimal sampling designs were determined and Monte Carlo simulations using the MAPB estimator were performed. The original model with the estimator was used to determine the predictive power of the sampling schemes. The most efficient sampling scheme (OSS-2) was accurate and precise in predicting apparent enoxaparin clearance (-3.2% bias, 6.5% precision). The addition of a third sampling time at 30 minutes (OSS-3) was more accurate (P < 0.01) and precise (P < 0.01) than OSS-2 at predicting the rate of absorption (ka) but did not improve the accuracy (P > 0.05) or precision (P = 0.20) of the CLs/F estimate. The determination of antifactor Xa activity at 5 and 24 hours, along with the Bayesian estimators generated from this study, accurately and precisely predict the apparent clearance of antifactor Xa activity. This sampling strategy may be used for therapeutic drug monitoring of enoxaparin and for future clinical trials in patients with chronic kidney disease.

Anti-factor Xa kinetics after intravenous enoxaparin in patients undergoing percutaneous coronary intervention: a population model analysis

AIM

Recent studies have suggested that intravenous (i.v.) enoxaparin could be used as antithrombotic therapy in patients ongoing percutaneous coronary intervention (PCI). However, anti-Xa pharmacokinetics following different i.v. dosing regimens is not clearly established.

METHODS

A population pharmacokinetic analysis was developed using anti-Xa activities measured in 546 patients who received a single 0.5 mg kg(-1) i.v. dose of enoxaparin immediately before PCI. Effects of higher doses (0.75 mg kg(-1) and 1 mg kg(-1)) and/or additional bolus after the initial administration were similarly simulated.

RESULTS

Enoxaparin anti-Xa time profiles were best described by a one-compartment model with zero-order kinetics. Mean population parameters (intersubject variability, %) were CL 1.2 l h(-1) (33), V 2.9 l (30) and zero-order input 0.25 h (24). With a single bolus of 0.5 mg kg(-1), the totality of the patients reached an effective anticoagulation level (anti-Xa >0.5 IU ml(-1)) and only 2.5% reached levels above 1.5 IU ml(-1). Simulations showed that greater doses (0.75 mg kg(-1) and 1 mg kg(-1)) prolonged the duration of anticoagulation (3.4 and 4.1 h, respectively) compared with the 0.5 mg kg(-1) bolus (2.7 h) and markedly increased the proportion (48% and 79%, respectively) of patients with anti-Xa levels >1.5 IU ml(-1). For delayed and/or prolonged procedures, patients could be administered a second bolus of half the initial dose in a time interval between 90 min to 2 h after in order to maintain similar anticoagulation profile levels.

CONCLUSIONS

A single 0.5 mg kg(-1) i.v. dose of enoxaparin reached anticoagulation levels adequately and should be safer compared with greater doses for anticoagulation in patients undergoing an elective PCI. An additional second bolus could be proposed in patients with delayed or prolonged procedures.

Administration of enoxaparin by continuous infusion in a naturalistic setting: analysis of renal function and safety

STUDY OBJECTIVE

To describe the clinical use and safety of continuous infusion (CI) enoxaparin in a naturalistic setting and to evaluate the influence of renal function on enoxaparin elimination.

DESIGN

Retrospective medical record review.

SETTING

1000-bed tertiary care teaching centre.

PATIENTS

Hospitalized patients that received enoxaparin by CI during a 2-year period.

INTERVENTIONS

None.

MEASUREMENTS

Specific details of dosage and monitoring were collected. Adverse drug reactions (ADR) were recorded. Creatinine clearance (CrCl) was calculated using Cockroft and Gault and Brater equations. A population pharmacokinetic analysis was performed using the non-linear mixed effect model (NONMEM). For patients located in the intensive care unit (ICU) and ward, POSTHOC pharmacokinetic parameter estimates were evaluated using the Wilcoxon rank-sum. Pearson correlation coefficient was calculated to determine the association between renal function and anti-Xa clearance.

MAIN RESULTS

Sixty-seven patients received enoxaparin by CI of which 61.2% were in the ward and 38.8% in the ICU. The average initial rate and duration of infusion were 5.2 mg/h and 5.6 days, respectively. The number of anti-Xa concentration measurements averaged five per patient. Nine patients experienced an ADR. The most frequent ADR was gastrointestinal bleeding (n = 4). Among the 67 patients, 48 had available anti-Xa concentrations and were included in the NONMEM model. The anti-Xa CL and volume of distribution for ICU and ward patients averaged 0.64 +/- 0.34 L/h, 10.6 +/- 1.55 L and 1.01 +/- 0.39 L/h, 9.08 +/- 1.17 L, respectively. CrCl was not a significant covariate when included in the NONMEM model, and the association between CrCl and anti-Xa clearance was not significant (R2 = 0.0005; P = 0.8916).

CONCLUSIONS

This study is the first to report the use and safety of prolonged CI enoxaparin. Pharmacokinetic parameters of enoxaparin differ in ICU vs. ward patients. Overall, we found the safety of CI to be comparable to subcutaneous administration. Also, we found no effect of renal function on enoxaparin elimination.

Non-ST-segment elevation acute coronary syndrome in patients with renal dysfunction: benefit of low-molecular-weight heparin alone or with glycoprotein IIb/IIIa inhibitors on outcomes. The Global Registry of Acute Coronary Events

AIMS

To determine whether low-molecular-weight heparin (LMWH)+glycoprotein (GP) IIb/IIIa inhibitors provide greater benefit than unfractionated heparin (UFH)+GP IIb/IIIa inhibitors, irrespective of renal status.

METHODS AND RESULTS

Patients in the Global Registry of Acute Coronary Events (GRACE) were divided into three groups according to creatinine clearance (CrCl): normal renal function (CrCl >60 mL/min), moderate renal dysfunction (30<CrCl< or =60 mL/min), and severe (CrCl< or =30 mL/min) renal dysfunction. Data were analysed from 11 881 patients with acute coronary syndrome (ACS). Patients with moderate (n=3705) or severe (n=982) renal dysfunction were at higher risk of adverse outcomes than those with normal renal function. Decreasing CrCl was an independent predictor of mortality at 30 days and in-hospital major bleeding. LMWH+GP IIb/IIIa inhibitors were used significantly less frequently in patients with severe (2.0%) or moderate (3.1%) renal dysfunction than in those with normal function (3.9%, P=0.0056). LMWH alone was more beneficial than UFH alone, irrespective of renal status. LMWH alone was an independent predictor of 30 day survival [odds ratio (OR) 0.56; 95% confidence interval (CI) 0.43-0.73] and lower risk of in-hospital bleeding (OR 0.66; 95% CI 0.48-0.92). Bleeding rates were significantly lower with LMWH+GP IIb/IIIa inhibitors than those with UFH+GP IIb/IIIa inhibitors. Use of UFH+GP IIb/IIIa inhibitors was an independent predictor of bleeding (OR 2.02; 95% CI 1.42-2.90) compared with UFH alone.

CONCLUSION

In patients with renal dysfunction and non-ST-segment elevation ACS, bleeding complications are more frequent and outcomes appear worse in individuals treated with UFH compared with LMWH. Combination therapy with LMWH and GP IIb/IIIa inhibitors appears to be better tolerated than with UFH and GP IIb/IIIa inhibitors.

Life-Threatening Hemorrhage After Dalteparin Therapy in a Patient with Impaired Renal Function

Dalteparin and other low-molecular-weight heparins are frequently used for the treatment of deep vein thrombosis and for other indications. Unlike unfractionated heparin (UFH), dalteparin is mainly cleared through the kidney; therefore, it can accumulate in patients with impaired renal function, increasing the risk of hemorrhage. An 84-year-old woman with chronic renal failure was hospitalized because of stenosis of a femorofibular bypass in her right leg. Peripheral transluminal angioplasty was performed successfully. Later the same day, Doppler sonography revealed deep vein thrombosis of the left lower leg. Treatment with dalteparin was started. The patient was discharged home 3 days later, with dalteparin to be continued at home. One day later, the patient was rehospitalized because of a pronounced hematoma on her flank. Her hemoglobin level had dropped to 5.5 g/dl. Treatment with dalteparin was stopped, and protamine 2500 U and two transfusions of packed red blood cells were administered. Treatment with UFH and oral anticoagulants were started because of a persistent risk for venous thrombosis. Thereafter, the patient's hemoglobin level remained stable, and no further bleeding episodes occurred. As long as systematic studies of the efficacy and safety of dalteparin in patients with severe renal impairment are lacking, dalteparin should be avoided or used only with close monitoring of antifactor Xa activity in these patients. As an alternative, UFH can be used because monitoring of UFH is well established and easier than it is with dalteparin. Renal impairment does not notably influence the short elimination half-life of UFH, which unlike that of dalteparin or other low-molecular-weight heparins allows for rapid dosage adjustments to prevent hemorrhage.

Safety profile of different low-molecular weight heparins used at therapeutic dose

Low-molecular weight heparins (LMWHs) have been shown to be as safe and effective as unfractionated heparin (UFH) for the treatment of acute venous thrombosis and non-life-threatening pulmonary embolism. Different reports have shown that LMWHs may also be used to treat patients with unstable angina or non-Q-wave infarction. The safety of LMWHs used at therapeutic dose has been widely studied in pivotal clinical trials and analysed in several meta-analyses. However, despite the wide development and use of LMWHs, several issues regarding the safety and optimal use of LMWHs remain unanswered. The main adverse effect of LMWHs is bleeding and it is uncertain whether a weight-adjusted dosage regimen without laboratory monitoring can be used in patients with a high risk of bleeding, such as patients with renal failure, elderly patients, obese patients or pregnant women. These patients are usually excluded from clinical trials and only a few studies, not sufficiently powered to estimate efficacy and safety, have been carried out in these special populations. Most of the available data comes from pharmacokinetic or population pharmacodynamic studies or clinical reports. Results in patients with renal impairment who are not undergoing haemodialysis suggest that a reduction in calculated creatinine clearance levels is associated with an increased risk of accumulation of anti-Xa activity, the extent of which differs depending on the individual LMWH and the extent to which the compound is cleared by the kidney. The limited data available regarding the use of therapeutic doses of LMWHs in obese patients suggest that there is no need to cap the dose at a maximal allowable dose. Long-term (3-month) treatment with LMWHs appears to be as effective and safe as oral anticoagulant therapy for the treatment of venous thromboembolism. It appears that each LMWH is a distinct compound with unique pharmacokinetic and pharmacodynamic profiles. Until more data are available regarding these special populations, periodic monitoring of anti-Xa activity levels may be recommended to detect accumulation and/or an overdose and minimise the bleeding risk. The non-haemorrhagic adverse effects of the LMWHs include heparin-induced thrombocytopenia (HIT) and osteoporosis. The incidence of HIT appears to be lower with LMWHs than with UFH; there is currently not enough data to compare the frequency of HIT between the various LMWHs. LMWHs also appear to carry a lower risk of causing osteoporosis than UFH. In conclusion, studies that include special population patients are required to make conclusive recommendations concerning the safety and monitoring of the different LMWHs.

Dosing strategy for enoxaparin in patients with renal impairment presenting with acute coronary syndromes

BACKGROUND

Phase III clinical studies have confirmed that enoxaparin is superior to standard heparin in reducing the rate of recurrent ischaemic events in patients with non-ST elevation acute coronary syndromes. Patients with moderate to severe renal impairment were, however, excluded from these studies. Due to the hydrophilic disposition of enoxaparin, accumulation is likely in patients with renal dysfunction, thereby increasing the risk of haemorrhagic complications if standard weight adjusted treatment doses are used. Arbitrary dose reduction has been reported to increase the risk of ischaemic events, presumably due to inadequate enoxaparin concentrations.

AIM

The aims of this study were to investigate the influence of glomerular filtration rate (GFR) on the pharmacokinetics of subcutaneously administered enoxaparin, and to develop a practical dosing algorithm in renal impairment that can easily be used at the bedside.

METHODS

Thirty-eight patients, median age 78 years (range 44-87), mean GFR 32 ml min(-1) (range 16-117) and mean weight 69 kg (range 32-95), presenting with acute coronary syndrome were recruited into the study. Approximately 10 anti-Xa concentrations were taken per patient over their period of therapy. A population pharmacokinetic model was developed using non linear mixed effects modelling techniques, utilizing the software NONMEM. Stochastic simulations were performed to identify the most suitable dosing regimen.

RESULTS

Three hundred and thirteen anti-Xa concentrations were collected. A two compartment, first order input model was identified as the best baseline model. Covariates found to improve model fitting were GFR as a linear function on clearance (CL) and weight as a linear function on the central volume compartment (Vc). The fraction of drug excreted unchanged (Fu) was estimated at 71%. CL and Vc from the final covariate model were estimated as; CL (l h(-1)) = 0.681 per 4.8 l hr(-1) (GFR) + 0.229 Vc (l) = 5.22 per 80 kg (total body weight)

CONCLUSIONS

Clearance of enoxaparin was predictably related to GFR estimated using the Cockroft and Gault equation, with ideal body weight used as the size descriptor. According to our model no dosage adjustment from the standard 1.0 mg kg(-1) 12 hourly is required for the first 48 h of treatment. Maintenance doses thereafter can be calculated using standard proportional adjustments based on Fu equal to 0.71.

Dosage of enoxaparin among obese and renal impairment patients

BACKGROUND

Enoxaparin dosage for obese patients and patients with renal impairment remains controversial.

OBJECTIVE

To compare anti-factor Xa activity (anti-Xa) among obese and renal impairment patients to patients with healthy weight and adequate renal function.

DESIGN

Open, prospective, nonrandomized clinical trial.

SETTING

A major community teaching hospital.

PATIENTS

A total of 233 patients with prescription of enoxaparin.

INTERVENTIONS

Enoxaparin 1.5 mg/kg once daily or 1 mg/kg twice daily except those on dialysis, who received 75% of the dose.

MEASUREMENTS

Anti-Xa was measured 4 h post-injection on day 2 or 3.

RESULTS

Mean (95% confidence interval (95% CI)) anti-Xa was equal to 1.14 IU/mL (1.07-1.21) and 1.14 IU/mL (1.08-1.20) among patients who received one (n=92) and two injections (n=122) per day, respectively. Anti-Xa increases with body mass index (BMI) (0.01 IU/mL for each kg/m2; 95% CI: 0.002-0.017), but the increase is insufficient to reach supratherapeutic anti-Xa. Anti-Xa decreases with higher creatinine clearance (CrCl) (-0.003 IU/mL for each mL/min; 95% CI: -0.006 to -0.001). On the twice-daily regimen, this is sufficient to reach supratherapeutic anti-Xa. The odd ratio (OR) (95% CI) of having a nontherapeutic anti-Xa is equal to 2.28 (1.25-4.16) when enoxaparin is administered twice daily and to 3.03 (1.16-7.86) among severe renal impairment patients (< or =30 mL/min).

CONCLUSIONS

Based on Anti-Xa, no dosage adjustments are required in obese patients. In renally impaired patients, adjustments may be necessary when enoxaparin is administered twice daily.