Antithrombin Concentrate Use in Children Receiving Unfractionated Heparin for Acute Thrombosis

Efficacy and safety of antithrombin supplementation in neonates and infants on a continuous heparin infusion

Background

Antithrombin (AT) is a natural anticoagulant and potent inhibitor of several coagulation proteins, including activated factor X (FXa) and FIIa. The therapeutic activity of heparin depends on the presence of AT. Levels of plasma AT are low in neonates and young infants compared to those in adults. Exogenous AT supplementation is postulated to enhance the activity of heparin and facilitate attainment of therapeutic anticoagulation in infants.

Objectives

To describe the efficacy and safety of AT administration in infants on a continuous heparin infusion.

Methods

Retrospective cohort study of 50 infants who received AT while on a heparin infusion. The primary efficacy outcome was attainment of therapeutic anticoagulation within 48 hours after AT administration. Secondary outcomes included the percent of partial thromboplastin time (PTT) levels and/or antifactor Xa (anti-FXa) activity within the therapeutic window, attainment of the target AT activity level, the incidence and severity of bleeding, and all-cause in-hospital mortality. A secondary analysis investigated the relationship between simultaneously measured PTT levels and anti-FXa activity used for heparin monitoring.

Results

AT supplementation resulted in achievement of at least one therapeutic PTT level or anti-FXa activity in 90% of AT courses, though not sustained. PTT was within the therapeutic window more often than anti-FXa activity. When measured simultaneously, therapeutic anti-FXa levels were associated with supratherapeutic PTT levels.

Conclusion

AT supplementation in infants on a continuous heparin infusion may transiently improve the therapeutic effect of heparin, but this is largely dependent on the laboratory parameters used for monitoring.

Questions around a case of in utero thrombosis in a premature child, concerning the management of anticoagulant treatments

We report the case of a preterm infant presenting a thrombosis, discovered on ultrasound at 22 weeks of gestational age and confirmed at birth following additional examinations. We describe the anticoagulant treatment of this patient by intravenous enoxaparin, tinzaparin and rivaroxaban, from questioning to practice.

Native and activated antithrombin inhibits TMPRSS2 activity and SARS-CoV-2 infection

Host cell proteases such as TMPRSS2 are critical determinants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) tropism and pathogenesis. Here, we show that antithrombin (AT), an endogenous serine protease inhibitor regulating coagulation, is a broad-spectrum inhibitor of coronavirus infection. Molecular docking and enzyme activity assays demonstrate that AT binds and inhibits TMPRSS2, a serine protease that primes the Spike proteins of coronaviruses for subsequent fusion. Consequently, AT blocks entry driven by the Spikes of SARS-CoV, MERS-CoV, hCoV-229E, SARS-CoV-2 and its variants of concern including Omicron, and suppresses lung cell infection with genuine SARS-CoV-2. Thus, AT is an endogenous inhibitor of SARS-CoV-2 that may be involved in COVID-19 pathogenesis. We further demonstrate that activation of AT by anticoagulants, such as heparin or fondaparinux, increases the anti-TMPRSS2 and anti-SARS-CoV-2 activity of AT, suggesting that repurposing of native and activated AT for COVID-19 treatment should be explored.

Antithrombin III Supplementation in a Premature Infant: Is There a Target Antithrombin Level?

The optimal antithrombin (AT) activity for low-molecular-weight heparin efficacy and the benefits of antithrombin III (ATIII) supplementation in premature infants diagnosed with venous thromboembolism are unknown. Currently, there are no neonatal-specific guidelines directing the appropriate target AT activity during supplementation. This case report describes a critically ill premature infant with a progressive, occlusive inferior vena cava thrombus who received supplemental ATIII during enoxaparin treatment. The patient did not achieve therapeutic anti-Xa levels despite increasing enoxaparin dosing to 3 mg/kg every 12 hours. ATIII supplementation sufficient to attain an AT activity of >40%, in combination with an enoxaparin dosing of >2 mg/kg every 12 hours, was needed to achieve therapeutic anti-Xa levels. Future large studies are needed to determine if there is an optimal target AT activity for critically ill premature infants.

Antithrombin Dose Optimization in Extracorporeal Membrane Oxygenation in Infants

Anticoagulation in extracorporeal membrane oxygenation (ECMO) is challenging, with significant morbidity and mortality associated with thrombotic complications. Unfractionated heparin (UFH) is commonly used, which depends on native antithrombin (AT) function to exert anticoagulant effects. Antithrombin deficiency is common in infants on ECMO and replacement with AT concentrate may be warranted. However, dosing recommendations in this population are limited. We conducted a retrospective review of patients <1 year of age who received recombinant AT (ATryn) while on UFH and ECMO between January 1, 2010 and December 31, 2017. Commonly used dosing equations were assessed to determine their ability to predict postdose AT levels. Patient AT levels were compared with equation-predicted postdose AT levels to determine a correlation. A total of 102 doses in 41 patients were used for analysis. Baseline mean AT level was 43% (±13%) and mean AT doses were 134 units (±58.1 units) or 40.5 units/kg (±18.7 units/kg). Median increase in the AT level was 8% (interquartile range 2-17%) with a mean postdose level of 52.6% (±14.2%). Weight-based dosing poorly correlated with postdose AT levels (r2 = 0.082). Postdose levels were best predicted when using an equation that included desired change in the AT level from baseline, the patient's weight, and added weight from the volume of the ECMO circuit (r2 = 0.427). Prospective studies are needed to evaluate optimal dosing strategies, safety, and efficacy of AT in this population.

Catheter-directed Thrombolysis for Neonatal IVC and Bilateral Renal Vein Thrombosis: A Case Report

Renal vein thrombosis is the most common non-catheter-associated venous thromboembolism event in neonates, accounting for up to 20% of cases. Although mortality rates are lower than a variety of other forms of pediatric thrombosis, renal vein thrombi are associated with significant short-term and long-term sequelae. This report presents the case of a full-term neonate presenting with bilateral renal vein thrombosis with inferior vena cava involvement treated with catheter-directed thrombolysis. This case report intends to highlight the value of a multidisciplinary approach to pediatric venous thromboembolism and to outline relevant procedural details and current laboratory and imaging monitoring of catheter-directed thrombolysis.

Hematologic concerns in extracorporeal membrane oxygenation

This ISTH "State of the Art" review aims to critically evaluate the hematologic considerations and complications in extracorporeal membrane oxygenation (ECMO). ECMO is experiencing a rapid increase in clinical use, but many questions remain unanswered. The existing literature does not address or explicitly state many pertinent details that may influence hematologic complications and, ultimately, patient outcomes. This review aims to broadly introduce modern ECMO practices, circuit designs, circuit materials, hematologic complications, transfusion-related considerations, age- and size-related differences, and considerations for choosing outcome measures. Relevant studies from the 2019 ISTH Congress in Melbourne, which further advanced our understanding of these processes, will also be highlighted.

Antithrombin Population Pharmacokinetics in Pediatric Ventricular Assist Device Patients

OBJECTIVES

Describe the pharmacokinetics of antithrombin in pediatric patients undergoing ventricular assist device therapy and provide dosing recommendations for antithrombin in this population.

DESIGN

A retrospective population pharmacokinetic study was designed.

SETTING

Large tertiary care children's hospital Subject inclusion criteria consisted of less than 19 years old.

PATIENTS

Subjects less than 19 years old undergoing therapy with a HeartWare ventricular assist device (HeartWare, Framingham, MA) or Berlin EXCOR ventricular assist device (Berlin GmbH, Berlin, Germany), who received a dose of antithrombin with a postdose antithrombin activity level from January 1, 2011, to June 30, 2017.

INTERVENTIONS

Population pharmacokinetic analysis and simulation using NONMEM v.7.4 (Icon, PLC, Dublin, Ireland).

MEASUREMENTS AND MAIN RESULTS

A total of 41 patients met study criteria (median age, 5.8 years [interquartile range, 1.6-9.9 yr]), and 53.7% underwent therapy with the pulsatile Berlin EXCOR pediatric ventricular assist device (Berlin Heart GmbH, Berlin, Germany). All patients received unfractionated heparin continuous infusion at a mean ± SD dose of 29 ± 14 U/kg/hr. A total of 181 antithrombin doses (44.1 ± 24.6 U/kg/dose) were included, and baseline antithrombin activity levels were 77 ± 12 U/dL. Antithrombin activity levels were drawn a median 19.9 hours (interquartile range, 8.8-41.6 hr) after antithrombin dose. A one-compartment proportional error model best fit the data, with allometric scaling of fat-free mass providing a better model fit than actual body weight. Unfractionated heparin and baseline antithrombin were identified as significant covariates. A 50 U/kg dose of antithrombin had a simulated half-life 13.2 ± 6.6 hours.

CONCLUSIONS

Antithrombin should be dosed on fat-free mass in pediatric ventricular assist device patients. Unfractionated heparin dose and baseline antithrombin activity level should be considered when dosing antithrombin in pediatric ventricular assist device patients.

Exogenous supplementation of antithrombin III in adult and pediatric patients receiving extracorporeal membrane oxygenation

Background:

Antithrombin III deficiency can occur with heparin anticoagulation during extracorporeal membrane oxygenation leading to heparin resistance. Antithrombin III supplementation has been shown to improve anticoagulation; however, there is no consensus on appropriate administration. We described the effect of antithrombin III supplementation on coagulation parameters in adult and pediatric extracorporeal membrane oxygenation patients.

Methods:

We conducted a retrospective cohort study using electronic medical records of patients who received ⩾1 dose of antithrombin III during extracorporeal membrane oxygenation while on continuous heparin. Endpoints included the change in anti-Xa levels and antithrombin III activity at −6 versus 6 h relative to antithrombin III supplementation, and heparin infusion rates at 6 versus 12 h after antithrombin III supplementation.

Results:

Eighteen patients receiving 36 antithrombin III administrations were analyzed. Mean (standard deviation) anti-Xa values at −6 versus 6 h were 0.15 (0.07) versus 0.24 (0.15) IU/mL ( p-value: 0.250) for pediatrics and 0.19 (0.22) versus 0.31 (0.27) IU/mL ( p-value: 0.052) for adults. Mean (standard deviation) plasma antithrombin III activity at the same intervals were 32% (14.2%) versus 66.8% (25.1%; p-value: 0.062) for pediatrics and 30.3% (14%) versus 52.8% (8.1%; p-value: 0.094) for adults. Mean (standard deviation) heparin rates at 6 versus 12 h after antithrombin III for pediatrics were 23.6 (6) versus 23.5 (6.5) units/kg/h ( p-value: 0.728), and 15.3 (6.6) versus 13.5 (8) units/kg/h ( p-value: 0.188) for adults.

Conclusion:

Administration of antithrombin III improved anti-Xa levels in both populations, however, did not significantly reduce heparin rates. Our findings suggest that the use of antithrombin III restores heparin responsiveness in patients with low antithrombin III activity and low anti-Xa activity.

Monitoring of heparins in antithrombin-deficient patients

INTRODUCTION

Heparins exert their anticoagulant effect through activation of antithrombin. Whether antithrombin deficiency leads to clinically relevantly reduced anti-Xa activity of heparins is unknown. We investigated the relation between antithrombin deficiency and anti-Xa activity measurements of plasma samples spiked with unfractionated heparin (UFH) or low-molecular-weight heparin (LMWH).

MATERIALS AND METHODS

Plasma samples from 34 antithrombin-deficient subjects and 17 family controls were spiked with UFH and LMWH (nadroparin) aimed to correspond with an anti-Xa activity of 0.8 IU/mL. Antithrombin, β-antithrombin and anti-Xa activities were measured.

RESULTS

Mean anti-Xa activity with LWMH was 0.55 IU/mL (0.30-0.74) (recovery 69%, 38-93%) in antithrombin-deficient subjects and 0.82 (0.71-0.89) IU/mL in controls (recovery 103%, 89-111%). Expected anti-Xa measurements after LMWH spiking were found in 17/17 non-deficient subjects and in 8/34 antithrombin-deficient subjects. Anti-Xa measurements in the expected range (0.6-1.0 IU/mL) after UFH spiking were found in 17/17 non-deficient subjects and in 1/22 antithrombin-deficient subjects. Antithrombin activity correlated with anti-Xa activity of UFH (R = 0.77) and LMWH (R = 0.66). Mixing studies of pooled normal plasma and antithrombin-deficient plasma showed that anti-Xa recovery was linearly reduced with antithrombin activity decreasing below 100%.

CONCLUSIONS

Reduced antithrombin activity causes significantly reduced anti-Xa levels. Standard LWMH- or UFH-doses are likely to lead to under treatment in antithrombin-deficient individuals.

Effect of Exogenous Antithrombin Administration on Anti-Xa Levels in Infants Treated With Enoxaparin

OBJECTIVES

Determine the effect of exogenous antithrombin III administration on low molecular weight heparin anti-Xa levels in the context of enoxaparin dosing in infants.

METHODS

A retrospective chart review of infants receiving concomitant antithrombin III and enoxaparin. The primary objective of this study was to determine the median change in anti-Xa level with antithrombin III supplementation. Secondary objectives were to analyze the median change in antithrombin III levels after administration of exogenous antithrombin III, the dosing of antithrombin III, and the dose of enoxaparin throughout therapy. For a safety analysis, any bleeding events were recorded.

RESULTS

The study included 17 patients who received a total of 33 doses of antithrombin III. The median change in anti-Xa levels in infants receiving exogenous antithrombin III was 0.2 units/mL (p < 0.001). The median dose of antithrombin III was 50 units/kg and was administered when patients were receiving a median enoxaparin dose of 1.71 mg/kg. The median increase in antithrombin III levels was 16.5% (p < 0.001).

CONCLUSIONS

These results demonstrated that administration of exogenous antithrombin III to infants who were being treated with enoxaparin results in a significant increase in anti-Xa levels. At this time, there is insufficient evidence to recommend routine administration of antithrombin III to infants on enoxaparin. However, antithrombin III supplementation could be considered a potential option for patients who are unable to adequately achieve therapeutic anti-Xa levels with enoxaparin alone.

Population pharmacokinetics of human antithrombin concentrate in paediatric patients

AIMS

Antithrombin is increasingly used in paediatric patients, yet there are few age-specific pharmacokinetic data to guide dosing. We aimed to describe the pharmacokinetic profile of human (plasma-derived) antithrombin concentrate in paediatric patients.

METHODS

A 5-year retrospective review was performed of patients <19 years of age admitted to our institution who received antithrombin concentrate, were not on mechanical circulatory support and had baseline (predose) and postdose plasma antithrombin activity levels available for analysis. Demographic and laboratory variables, antithrombin dosing information and data on the use of continuous infusion unfractionated heparin were collected. Population pharmacokinetic analysis was performed with bootstrap analysis. The model developed was tested against a validation dataset from a cohort of similar patients, and a predictive value was calculated.

RESULTS

A total 184 patients met the study criteria {46.7% male, median age [years] 0.35 [interquartile range (IQR) 0.07-3.9]}. A median of two antithrombin doses (IQR 1-4) were given to patients (at a dose of 46.3 ± 13.6 units kg^-1 ), with median of three (IQR 2-7) postdose levels per patient. Continuous infusion unfractionated heparin was administered in 87.5% of patients, at a mean dose of 34.1 ± 22.7 units kg^-1 h^-1 . A one-compartment exponential error model best fit the data, and significant covariates included allometrically scaled weight on clearance and volume of distribution, unfractionated heparin dose on clearance, and baseline antithrombin activity level on volume of distribution. The model resulted in a median -1.75% prediction error (IQR -11.75% to 6.5%) when applied to the validation dataset (n = 30).

CONCLUSIONS

Antithrombin pharmacokinetics are significantly influenced by the concurrent use of unfractionated heparin and baseline antithrombin activity.

Transient Hemi-Lower Limb Ischemia in the Newborn: Arterial Thrombosis or Persistent Sciatic Artery?

Neonatal thromboembolism occurs with various predispositions and triggers. Early diagnosis of the thrombosis is challenging and essential for the therapeutic interventions. We herein report two newborns who presented with transient hemi-lower limb ischemia due to (1) arterial thrombosis or (2) a persistent sciatic artery (PSA). The patient with arterial thrombosis showed elevations of fibrin degradation product and D-dimer and received antithrombin and heparin intravenously. The patient with PSA was immediately assessed by a contrast-enhanced computed tomography because of a transient ischemic episode with no evidence of hypercoagulability. Newborns suspected of having arterial thrombosis may need urgent surgical intervention along with thrombolytic and anticoagulant therapy to prevent organ ischemia and amputation of extremities. Conversely, some PSA cases have reportedly been treated conservatively. This vascular anomaly was previously reported as a cause of lower limb ischemia only in a newborn. PSA is a critical differential diagnosis of neonatal arterial thrombosis that needs urgent therapeutic intervention.

Use and Future Investigations of Recombinant and Plasma-Derived Coagulation and Anticoagulant Products in the Neonate

Although congenital bleeding disorders can manifest in the newborn period, the most common causes of bleeding and thrombosis in neonates are acquired conditions. Factor concentrates are used for specific diagnoses (hemophilia with inhibitors, specific factor deficiency, von Willebrand disease) and approved indications, and increasingly for off-label indications (bleeding in surgery cardiopulmonary bypass, extracorporeal membrane oxygenation). We will review the approved indications for factor products in the neonate and discuss the evidence and rationale for off-label use of factor products in management of bleeding and thrombosis in the neonate.

Antithrombin III for critically ill patients: a systematic review with meta-analysis and trial sequential analysis

Purpose

Antithrombin III (AT III) is an anticoagulant with anti-inflammatory properties. We assessed the benefits and harms of AT III in critically ill patients.

Methods

We searched from inception to 27 August 2015 in CENTRAL, MEDLINE, EMBASE, CAB, BIOSIS and CINAHL. We included randomized controlled trials (RCTs) irrespective of publication status, date of publication, blinding status, outcomes published or language.

Results

We included 30 RCTs with a total of 3933 participants. The majority of included trials were at high risk of bias. Combining all trials, regardless of bias, showed no statistically significant effect of AT III on mortality (RR 0.95, 95 % CI 0.88–1.03, I² = 0 %, fixed-effect model, 29 trials, 3882 participants). Among those with severe sepsis and disseminated intravascular coagulation (DIC), AT III showed no impact on mortality (RR 0.95, 95 % Cl 0.88–1.03, I² = 0 %, fixed-effect model, 12 trials, 2858 participants). We carried out multiple subgroup and sensitivity analyses to assess the benefits and harms of AT III and to examine the impact of risk of bias. AT III significantly increased bleeding events (RR 1.58, 95 % CI 1.35–1.84, I² = 0 %, fixed-effect model, 11 trials, 3019 participants). However, for all other outcome measures and analyses, the results did not reach statistical significance.

Conclusions

There is insufficient evidence to support AT III substitution in any category of critically ill participants including those with sepsis and DIC. AT III did not show an impact on mortality, but increased the risk of bleeding.

Electronic supplementary material

The online version of this article (doi:10.1007/s00134-016-4225-7) contains supplementary material, which is available to authorized users.

Antithrombin III for critically ill patients

BACKGROUND

Critical illness is associated with uncontrolled inflammation and vascular damage which can result in multiple organ failure and death. Antithrombin III (AT III) is an anticoagulant with anti-inflammatory properties but the efficacy and any harmful effects of AT III supplementation in critically ill patients are unknown. This review was published in 2008 and updated in 2015.

OBJECTIVES

To examine:1. The effect of AT III on mortality in critically ill participants.2. The benefits and harms of AT III.We investigated complications specific and not specific to the trial intervention, bleeding events, the effect on sepsis and disseminated intravascular coagulation (DIC) and the length of stay in the intensive care unit (ICU) and in hospital in general.

SEARCH METHODS

We searched the following databases from inception to 27 August 2015: Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (Ovid SP), EMBASE (Ovid SP,), CAB, BIOSIS and CINAHL. We contacted the main authors of trials to ask for any missed, unreported or ongoing trials.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) irrespective of publication status, date of publication, blinding status, outcomes published, or language. We contacted the investigators and the trial authors in order to retrieve missing data. In this updated review we include trials only published as abstracts.

DATA COLLECTION AND ANALYSIS

Our primary outcome measure was mortality. Two authors each independently abstracted data and resolved any disagreements by discussion. We presented pooled estimates of the intervention effects on dichotomous outcomes as risk ratios (RR) with 95% confidence intervals (CI). We performed subgroup analyses to assess risk of bias, the effect of AT III in different populations (sepsis, trauma, obstetrics, and paediatrics), and the effect of AT III in patients with or without the use of concomitant heparin. We assessed the adequacy of the available number of participants and performed trial sequential analysis (TSA) to establish the implications for further research.

MAIN RESULTS

We included 30 RCTs with a total of 3933 participants (3882 in the primary outcome analyses).Combining all trials, regardless of bias, showed no statistically significant effect of AT III on mortality with a RR of 0.95 (95% CI 0.88 to 1.03), I² statistic = 0%, fixed-effect model, 29 trials, 3882 participants, moderate quality of evidence). For trials with low risk of bias the RR was 0.96 (95% Cl 0.88 to 1.04, I² statistic = 0%, fixed-effect model, 9 trials, 2915 participants) and for high risk of bias RR 0.94 (95% Cl 0.77 to 1.14, I² statistic = 0%, fixed-effect model, 20 trials, 967 participants).For participants with severe sepsis and DIC the RR for mortality was non-significant, 0.95 (95% Cl 0.88 to 1.03, I² statistic = 0%, fixed-effect model, 12 trials, 2858 participants, moderate quality of evidence).We conducted 14 subgroup and sensitivity analyses with respect to the different domains of risk of bias, but detected no statistically significant benefit in any subgroup analyses.Our secondary objective was to assess the benefits and harms of AT III. For complications specific to the trial intervention the RR was 1.26 (95% Cl 0.83 to 1.92, I² statistic = 0%, random-effect model, 3 trials, 2454 participants, very low quality of evidence). For complications not specific to the trial intervention, the RR was 0.71 (95% Cl 0.08 to 6.11, I² statistic = 28%, random-effects model, 2 trials, 65 participants, very low quality of evidence). For complications other than bleeding, the RR was 0.72 ( 95% Cl 0.42 to 1.25, I² statistic = 0%, fixed-effect model, 3 trials, 187 participants, very low quality of evidence). Eleven trials investigated bleeding events and we found a statistically significant increase, RR 1.58 (95% CI 1.35 to 1.84, I² statistic = 0%, fixed-effect model, 11 trials, 3019 participants, moderate quality of evidence) in the AT III group. The amount of red blood cells administered had a mean difference (MD) of 138.49 (95% Cl -391.35 to 668.34, I² statistic = 84%, random-effect model, 4 trials, 137 participants, very low quality of evidence). The effect of AT III in patients with multiple organ failure (MOF) was a MD of -1.24 (95% Cl -2.18 to -0.29, I² statistic = 48%, random-effects model, 3 trials, 156 participants, very low quality of evidence) and for patients with an Acute Physiology and Chronic Health Evaluation score (APACHE) at II and III the MD was -2.18 (95% Cl -4.36 to -0.00, I² statistic = 0%, fixed-effect model, 3 trials, 102 participants, very low quality of evidence). The incidence of respiratory failure had a RR of 0.93 (95% Cl 0.76 to 1.14, I² statistic = 32%, random-effects model, 6 trials, 2591 participants, moderate quality of evidence). AT III had no statistically significant impact on the duration of mechanical ventilation (MD 2.20 days, 95% Cl -1.21 to 5.60, I² statistic = 0%, fixed-effect model, 3 trials, 190 participants, very low quality of evidence); on the length of stay in the ICU (MD 0.24, 95% Cl -1.34 to 1.83, I² statistic = 0%, fixed-effect model, 7 trials, 376 participants, very low quality of evidence) or on the length of stay in hospital in general (MD 1.10, 95% Cl -7.16 to 9.36), I² statistic = 74%, 4 trials, 202 participants, very low quality of evidence).

AUTHORS' CONCLUSIONS

There is insufficient evidence to support AT III substitution in any category of critically ill participants including the subset of patients with sepsis and DIC. We did not find a statistically significant effect of AT III on mortality, but AT III increased the risk of bleeding events. Subgroup analyses performed according to duration of intervention, length of follow-up, different patient groups, and use of adjuvant heparin did not show differences in the estimates of intervention effects. The majority of included trials were at high risk of bias (GRADE; very low quality of evidence for most of the analyses). Hence a large RCT of AT III is needed, without adjuvant heparin among critically ill patients such as those with severe sepsis and DIC, with prespecified inclusion criteria and good bias protection.

Antithrombin: anti-inflammatory properties and clinical applications

Many humoral and cellular components participate in bidirectional communication between the coagulation and inflammation pathways. Natural anticoagulant proteins, including antithrombin (AT), tissue factor pathway inhibitor, and protein C, suppress proinflammatory mediators. Conversely, inflammation blunts anticoagulant activity and, when uncontrolled, promotes systemic inflammation-induced coagulation, such as those that occur in disseminated intravascular coagulation and severe sepsis. This review discusses the mechanisms of action and clinical use of AT concentrate in critically ill patients and in the settings of perioperative anticoagulation management for surgery and obstetrics. AT is a serine protease inhibitor with broad anticoagulant activity and potent anti-inflammatory properties. In clinical conditions associated with hereditary or acquired AT deficiency, administration of AT concentrate has been shown to restore proper haemostasis and attenuate inflammation. Of note, AT modulates inflammatory responses not only by inhibiting thrombin and other clotting factors that induce cytokine activity and leukocyte-endothelial cell interaction, but also by coagulation-independent effects, including direct interaction with cellular mediators of inflammation. An increasing body of evidence suggests that AT concentrate may be a potential therapeutic agent in certain clinical settings associated with inflammation. In addition to the well-known anticoagulation properties of AT for the treatment of hereditary AT deficiency, AT also possesses noteworthy anti-inflammatory properties that could be valuable in treating acquired AT deficiency, which often result in thrombotic states associated with an inflammatory component.