Pharmacokinetics and pharmacodynamics of argatroban in combination with a platelet glycoprotein IIB/IIIA receptor antagonist in patients undergoing percutaneous coronary intervention

Racial and Ethnic Differences in Response to Anticoagulation: A Review of the Literature

INTRODUCTION

Anticoagulants are among the most frequently prescribed medications in the United States. Racial and ethnic disparities in incidence and outcomes of thrombotic disorders are well-documented, but differences in response to anticoagulation are incompletely understood.

OBJECTIVE

The objective of this review is to describe the impact of race and ethnicity on surrogate and clinical end points related to anticoagulation and discuss racial or ethnic considerations for prescribing anticoagulants.

METHODS

A PubMed and MEDLINE search of clinical trials published between 1950 and May 2018 was conducted using search terms related to anticoagulation, specific anticoagulant drugs, race, and ethnicity. References of identified studies were also reviewed. English-language human studies on safety or efficacy of anticoagulants reporting data for different races or ethnicities were eligible for inclusion.

RESULTS

Seventeen relevant studies were identified. The majority of major trials reviewed for inclusion either did not include representative populations or did not report on the racial breakdown of participants. Racial differences in pharmacokinetics, dosing requirements, drug response, and/or safety end points were identified for unfractionated heparin, enoxaparin, argatroban, warfarin, rivaroxaban, and edoxaban.

CONCLUSIONS

Race appears to influence drug concentrations, dosing, or safety for some but not all direct oral anticoagulants. This information should be considered when selecting anticoagulant therapy for nonwhite individuals.

Antiplatelet Effect of a Pulaimab [Anti-GPIIb/IIIa F(ab)2 Injection] Evaluated by a Population Pharmacokinetic-pharmacodynamic Model

BACKGROUND

Cardiovascular disease has one of the highest mortality rates among all the diseases. Platelets play an important role in the pathogenesis of cardiovascular diseases. Platelet membrane glycoprotein GPIIb/IIIa antagonists are the most effective antiplatelet drugs, and pulaimab is one of these. The study aims to promote individual medication of pulaimab [anti-GPIIb/IIIa F(ab)2 injection] by discovering the pharmacological relationship among the dose, concentration, and effects. The goal of this study is to establish a population pharmacokineticpharmacodynamic model to evaluate the antiplatelet effect of intravenous pulaimab injection.

METHODS

Data were collected from 59 healthy subjects who participated in a Phase-I clinical trial. Plasma concentration was used as the pharmacokinetic index, and platelet aggregation inhibition rate was used as the pharmacodynamic index. The basic pharmacokinetics model was a two-compartment model, whereas the basic pharmacodynamics model was a sigmoid-EMAX model with a direct effect. The covariable model was established by a stepwise method. The final model was verified by a goodness-of-fit method, and predictive performance was assessed by a Bootstrap (BS) method.

RESULTS

In the final model, typical population values of the parameters were as follows: central distribution Volume (V1), 183 L; peripheral distribution Volume (V2), 349 L; Central Clearance (CL), 31 L/h; peripheral clearance(Q), 204 L/h; effect compartment concentration reaching half of the maximum effect (EC50), 0.252 mg/L; maximum effect value (EMAX), 54.0%; and shape factor (γ), 0.42. In the covariable model, thrombin time had significant effects on CL and EMAX. Verification by the goodness-of-fit and BS methods showed that the final model was stable and reliable.

CONCLUSION

A model was successfully established to evaluate the antiplatelet effect of intravenous pulaimab injection that could provide support for the clinical therapeutic regimen.

Prediction of paraquat exposure and toxicity in clinically ill poisoned patients: a model based approach

AIMS

Paraquat poisoning is a medical problem in many parts of Asia and the Pacific. The mortality rate is extremely high as there is no effective treatment. We analyzed data collected during an ongoing cohort study on self-poisoning and from a randomized controlled trial assessing the efficacy of immunosuppressive therapy in hospitalized paraquat-intoxicated patients. The aim of this analysis was to characterize the toxicokinetics and toxicodynamics of paraquat in this population.

METHODS

A non-linear mixed effects approach was used to perform a toxicokinetic/toxicodynamic population analysis in a cohort of 78 patients.

RESULTS

The paraquat plasma concentrations were best fitted by a two compartment toxicokinetic structural model with first order absorption and first order elimination. Changes in renal function were used for the assessment of paraquat toxicodynamics. The estimates of toxicokinetic parameters for the apparent clearance, the apparent volume of distribution and elimination half-life were 1.17 l h(-1) , 2.4 l kg(-1) and 87 h, respectively. Renal function, namely creatinine clearance, was the most significant covariate to explain between patient variability in paraquat clearance.This model suggested that a reduction in paraquat clearance occurred within 24 to 48 h after poison ingestion, and afterwards the clearance was constant over time. The model estimated that a paraquat concentration of 429 μg l(-1) caused 50% of maximum renal toxicity. The immunosuppressive therapy tested during this study was associated with only 8% improvement of renal function.

CONCLUSION

The developed models may be useful as prognostic tools to predict patient outcome based on patient characteristics on admission and to assess drug effectiveness during antidote drug development.

Argatroban therapy in heparin-induced thrombocytopenia

Argatroban is a direct thrombin inhibitor approved for anticoagulation in heparin-induced thrombocytopenia (HIT; in several countries) and in patients with or at risk of HIT undergoing percutaneous coronary intervention (PCI; in the USA). HIT is a relatively common extreme prothrombotic condition. When HIT is reasonably suspected, an alternative anticoagulant should be promptly initiated. In historical controlled studies, argatroban reduced new thrombosis, mortality from thrombosis and the composite of death, amputation or thrombosis, without increasing bleeding. With intravenous infusion, advantages include short half-life, easy monitoring and elimination primarily by hepatobiliary (rather than renal) means. In patients undergoing PCI, argatroban with or without glycoprotein IIb/IIIa inhibition leads to high rates of procedural success with low bleeding risk. Herein we review argatroban therapy for HIT and for PCI.

A guide to rational dosing of monoclonal antibodies

BACKGROUND AND OBJECTIVE

Dosing of therapeutic monoclonal antibodies (mAbs) is often based on body size, with the perception that body size-based dosing would reduce inter-subject variability in drug exposure. However, most mAbs are target specific with a relatively large therapeutic window and generally a small contribution of body size to pharmacokinetic variability. Therefore, the dosing paradigm for mAbs should be assessed in the context of these unique characteristics. The objective of this study was to review the current dosing strategy and to provide a scientific rationale for dosing of mAbs using a modelling and simulation approach.

METHODS

In this analysis, the body weight-based or body weight-independent (fixed) dosing regimens for mAbs were systematically evaluated. A generic two-compartment first-order elimination model was developed. Individual or population pharmacokinetic profiles were simulated as a function of the body weight effects on clearance (θ(BW_CL)) and on the central volume of distribution (θ(BW_V1)). The variability in exposure (the area under the serum concentration-time curve [AUC], trough serum concentration [C(min)] and peak serum concentration [C(max)]) was compared between body weight-based dosing and fixed dosing in the entire population. The deviation of exposure for light and heavy subjects from median body weight subjects was also measured. The simulation results were then evaluated with clinical pharmacokinetic characteristics of various mAbs that were given either by body weight-based dosing or by fixed dosing in the case study.

RESULTS

Results from this analysis demonstrated that exposure variability was dependent on the magnitude of the body weight effect on pharmacokinetics. In contrast to the conventional assumption, body weight-based dosing does not always offer advantages over fixed dosing in reducing exposure variability. In general, when the exponential functions of θ(BW_CL) and θ(BW_V1) in the population pharmacokinetic model are <0.5, fixed dosing results in less variability and less deviation than body weight-based dosing; when both θ(BW_CL) and θ(BW_V1) are >0.5, body weight-based dosing results in less variability and less deviation than fixed dosing. In the scenarios when either θ(BW_CL) or θ(BW_V1) is >0.5, the impact on exposure variability is different for each exposure measure. The case study demonstrated that most mAbs had little effect or a moderate body weight effect (θ(BW_CL) and θ(BW_V1) <0.5 or ∼0.5). The difference of variability in exposure between body weight-based and fixed dosing is generally less than 20% and the percentages of deviation for light and heavy subpopulations are less than 40%.

CONCLUSIONS

The analysis provided insights into the conditions under which either fixed or body weight-based dosing would be superior in reducing pharmacokinetic variability and exposure differences between light and heavy subjects across the population. The pharmacokinetic variability introduced by either dosing regimen is moderate relative to the variability generally observed in pharmacodynamics, efficacy and safety. Therefore, mAb dosing can be flexible. Given many practical advantages, fixed dosing is recommended to be the first option in first-in-human studies with mAbs. The dosing strategy in later stages of clinical development could then be determined based on combined knowledge of the body weight effect on pharmacokinetics, safety and efficacy from the early clinical trials.

Pharmacology of argatroban

Argatroban is a synthetic, small-molecule direct thrombin inhibitor that is approved in the USA, the EU and Japan for prophylaxis or treatment of thrombosis in patients with heparin-induced thrombocytopenia (HIT), and for anticoagulation of HIT patients undergoing PCI. Argatroban binds reversibly to, and inhibits both soluble and clot-bound thrombin. Argatroban does not generate antibodies, is not susceptible to degradation by proteases and is cleared hepatically. It has a predictable anticoagulant effect and there is a good correlation between dose, plasma concentration and pharmacodynamic effect. Initial clinical studies suggest that further investigations to establish the use of argatroban in ischemic stroke, acute coronary syndrome, hemodialysis, blood oxygenation, off-pump cardiac surgery and other clinical indications are warranted.

Pharmacotherapy in the critically ill obese patient

Despite the growing epidemic of obesity in the United States, dosing medications in such patients remains poorly studied and understood. Most recommendations are based on small independent studies, case reports, and expert opinion. Applying manufacturer kinetics and dosing recommendations in the obese patient may result in toxicity or treatment failure, leading to increased morbidity, mortality, and hospital length of stay.

Impact of renal function on argatroban therapy during percutaneous coronary intervention

Argatroban, a hepatically metabolized direct thrombin inhibitor, is approved for anticoagulation in patients with or at risk of heparin-induced thrombocytopenia (HIT) undergoing percutaneous coronary intervention (PCI). We investigated the effect of renal function on argatroban therapy during PCI. From previous argatroban studies in PCI, we evaluated relationships between estimated creatinine clearance (CrCl) and activated clotting times (ACTs), dosage, and outcomes in 219 patients with or at risk of HIT (HIT group, n = 67) or administered glycoprotein IIb/IIIa inhibition (non-HIT group, n = 152). Patients received an argatroban bolus (350 mcg/kg, HIT group; 250 or 300 mcg/kg, non-HIT group) then 25-30 mcg/kg/min (adjusted to achieve ACTs 300-450 s, HIT group) or 15 mcg/kg/min (target ACTs 275-325 s, non-HIT group), with additional 150-mcg/kg boluses if needed. Of 219 patients, 55 (25%) had CrCl <or= 60 ml/min (8 with CrCl <or= 30 ml/min). Regression analyses detected no association between CrCl (range 7-231 ml/min) and initial ACT (by bolus) or mean infusion dose. Multi-bolus usage was similar in patients with, versus without, CrCl <or= 60 ml/min. In the non-HIT group, CrCl was associated (P = 0.01) with the time to ACT <or= 160 s after argatroban cessation (approximately 17 min slower per 30-ml/min CrCl decrease). Eight patients (none with CrCl <or= 60 ml/min) had ischemic complications. Three patients (1 with CrCl 40 ml/min) experienced major bleeding. Argatroban dose adjustment for renal function appears unnecessary during PCI. Renal dysfunction may be associated with slower (by minutes) ACT effect decay after argatroban cessation. Argatroban is well tolerated in PCI patients with renal impairment.

Pharmacokinetics and pharmacodynamics of monoclonal antibodies: concepts and lessons for drug development

Monoclonal antibodies (mAbs) have complex pharmacology; pharmacokinetics and pharmacodynamics depend on mAb structure and target antigen. mAbs targeting soluble antigens often exhibit linear pharmacokinetic behavior, whereas mAbs targeting cell surface antigens frequently exhibit nonlinear behavior due to receptor-mediated clearance. Where nonlinear kinetics exist, clearance can change due to receptor loss following repeated dosing and/or disease severity. mAb pharmacodynamics are often indirect, with delayed clinically relevant outcomes. This behavior provides challenges during clinical development; studies must be carefully planned to account for complexities specific to each agent. Selection of a starting dose for human studies can be difficult. Species differences in pharmacology need to be considered. Various metrics are available for scaling from animals to humans. Optimal dose selection should ensure uniform mAb exposure across all individuals. Traditional approaches such as flat dosing and variable dosing based upon body surface area or weight should be supported by pharmacokinetic and pharmacodynamic behavior, including target antigen and concurrent disease states. The use of loading doses or dose adjustments to improve clinical response is also a consideration. The evaluation of drug interactions requires innovative designs. Due to the pharmacokinetic properties of mAbs, interacting drugs may need to be administered for protracted periods. Consequently, population pharmacokinetic and pharmacodynamic model-based approaches are often implemented to evaluate mAb drug interactions.

Reducing harm associated with anticoagulation: practical considerations of argatroban therapy in heparin-induced thrombocytopenia

Argatroban is a hepatically metabolized, direct thrombin inhibitor used for prophylaxis or treatment of thrombosis in heparin-induced thrombocytopenia (HIT) and for patients with or at risk of HIT undergoing percutaneous coronary intervention (PCI). The objective of this review is to summarize practical considerations of argatroban therapy in HIT. The US FDA-recommended argatroban dose in HIT is 2 microg/kg/min (reduced in patients with hepatic impairment and in paediatric patients), adjusted to achieve activated partial thromboplastin times (aPTTs) 1.5-3 times baseline (not >100 seconds). Contemporary experiences indicate that reduced doses are also needed in patients with conditions associated with hepatic hypoperfusion, e.g. heart failure, yet are unnecessary for renal dysfunction, adult age, sex, race/ethnicity or obesity. Argatroban 0.5-1.2 microg/kg/min typically supports therapeutic aPTTs. The FDA-recommended dose during PCI is 25 microg/kg/min (350 microg/kg initial bolus), adjusted to achieve activated clotting times (ACTs) of 300-450 sec. For PCI, argatroban has not been investigated in hepatically impaired patients; dose adjustment is unnecessary for adult age, sex, race/ethnicity or obesity, and lesser doses may be adequate with concurrent glycoprotein IIb/IIIa inhibition. Argatroban prolongs the International Normalized Ratio, and published approaches for monitoring the argatroban-to-warfarin transition should be followed. Major bleeding with argatroban is 0-10% in the non-interventional setting and 0-5.8% periprocedurally. Argatroban has no specific antidote, and if excessive anticoagulation occurs, argatroban infusion should be stopped or reduced. Improved familiarity of healthcare professionals with argatroban therapy in HIT, including in special populations and during PCI, may facilitate reduction of harm associated with HIT (e.g. fewer thromboses) or its treatment (e.g. fewer argatroban medication errors).

Effect of body mass index on Argatroban therapy during percutaneous coronary intervention

BACKGROUND

Obesity is common in patients undergoing percutaneous coronary intervention (PCI). Argatroban, a direct thrombin inhibitor, is used during PCI in patients with or at risk of heparin-induced thrombocytopenia (HIT) and also has been evaluated in conjunction with glycoprotein IIb/IIIa inhibition in nonHIT patients. We investigated the effect of body mass index (BMI), and specifically obesity (BMI>30 kg/m2), on argatroban therapy during PCI.

METHODS

From previously reported studies of argatroban therapy during PCI in patients with or at risk of HIT (ie, HIT group) or in conjunction with glycoprotein IIb/IIIa inhibition (ie, nonHIT group), we identified patients with sufficient data to determine BMI. After an initial bolus of 350 microg/kg (HIT group) or 300 or 250 microg/kg (nonHIT group), patients received continuous argatroban 25-30 microg/kg/min (adjusted to achieve ACTs of 300-450 s, HIT group) or 15 microg/kg/min (target ACTs of 275-325 s, nonHIT group) during PCI, with additional 150 microg/kg boluses allowed if needed. Regression analyses evaluated relationships between patient BMI and ACT response to initial bolus administration, mean infusion dose (HIT group only), and rate of ACT decline after PCI. Frequencies of additional bolus usage and clinical outcomes were compared between obese and nonobese patients.

RESULTS

Our analysis population included 225 patients (85 obese) in total: 73 in the HIT group and 152 in the nonHIT group (300 microg/kg bolus, n=101; 250 microg/kg bolus, n=51), with BMIs of 16.3-50.9 kg/m2. No association was detected between BMI and the first ACT after bolus administration (median ACTs of 361, 298, and 289 s, respectively, following 350, 300, and 250 microg/kg bolus), mean infusion dose (24.2+/-4.9 microg/kg/min overall in HIT group), or time to ACTs<or=160 s after argatroban cessation (median 4.4 h in HIT group and 1.7-2.1 h in nonHIT group). Fifteen (5 obese) patients in the HIT group and 36 (13 obese) in the nonHIT group required additional boluses, without differences by obesity versus nonobesity (P>or=0.35). Clinical outcomes did not differ (P>or=0.09) between obese and nonobese individuals: 4 (3 obese) patients in the HIT group and 4 (2 obese) in the nonHIT group had ischemic complications; 1 nonobese patient in the HIT group and 2 (1 obese) in the nonHIT group experienced major bleeding.

CONCLUSIONS

These findings support the use of actual body weight-adjusted (and ACT-targeted) argatroban therapy during PCI and suggest that dose adjustment for obesity (BMI up to 50.9 kg/m2) is unnecessary.

Update on the clinical applications of argatroban

The small molecule, arginomimetic drug argatroban is the first synthetic direct antithrombin to be approved for clinical use. Argatroban reversibly binds to and inhibits both soluble and clot-bound thrombin. In contrast to other direct thrombin inhibitors, argatroban upregulates nitric oxide, enhancing its antithrombotic effect, does not generate antibodies, is not susceptible to degradation by proteases and is hepatically cleared. It has a predictable anticoagulant effect. Argatroban has proven efficacy and safety for prophylaxis and treatment of patients with thrombosis associated with heparin-induced thrombocytopenia (HIT), and for percutaneous coronary intervention in HIT and non-HIT patients. Pilot studies suggest that further investigations to establish the use of argatroban in ischemic stroke, acute coronary syndrome, hemodialysis, blood oxygenation, off-pump cardiac surgery and other clinical indications are warranted.

Argatroban: update

Unfractionated heparin has historically been used as the anticoagulant of choice in the management of a number of thrombotic diseases. Recognition of the limitations of heparin has led to the development of a newer class of anticoagulants, the direct thrombin inhibitors. Argatroban is a synthetic small molecule that selectively inhibits thrombin at its active site. In preclinical studies, argatroban has been shown to be more effective than heparin in preventing arterial thrombosis and in promoting vessel patency in conjunction with thrombolysis in a number of animal models. In clinical trials, argatroban has been shown to be as effective as heparin in the management of ST-segment elevation myocardial infarction in conjunction with thrombolysis. It has been shown to be an effective anticoagulant in patients undergoing percutaneous coronary interventions. In patients with heparin-induced thrombocytopenia and heparin-induced thrombocytopenia complicated by thrombosis, argatroban significantly decreases the risk of thrombotic events. Small studies have demonstrated a potential role for its use in ischemic stroke and hemodialysis. Additional studies are warranted to confirm argatroban's efficacy in a wide variety of clinical settings.

Alternative parenteral anticoagulation with argatroban, a direct thrombin inhibitor

Argatroban, a direct thrombin inhibitor, effectively inhibits free and clot-bound thrombin without the need of a cofactor and exerts dose-dependent anticoagulant effects that are rapidly active and rapidly reversible (elimination half-life: 39-51 min). Argatroban provides predictable parenteral anticoagulation and is well tolerated with an acceptably low bleeding risk in a variety of clinical settings, including heparin-induced thrombocytopenia, acute ischemic stroke, percutaneous coronary intervention and hemodialysis. This review will discuss the clinical pharmacology and utility of argatroban; in particular, clinical trial experiences will be discussed in patients with, or at risk of, heparin-induced thrombocytopenia (where heparins must be avoided) including those requiring hemodialysis or percutaneous coronary intervention, and in patients with acute ischemic stroke (where heparins are not generally recommended).