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Heparin-induced thrombocytopenia (HIT) is a rare, potentially life-threatening condition secondary to unfractionated heparin or low molecular weight heparin exposure. This immune-mediated drug reaction manifests as thrombocytopenia with a paradoxical hypercoagulable state that can result in life-threatening thrombosis. It is imperative to ensure cessation of heparin-based products as soon as HIT is identified. Traditional treatment options include argatroban, bivalirudin, fondaparinux, and danaparoid with a transition to warfarin upon platelet recovery. These anticoagulants are notwithstanding limitations including parenteral administration and routine laboratory monitoring leading to prolonged hospitalizations, emphasizing the need for new therapies. Direct oral anticoagulants (DOACs) have been increasingly investigated for the management of HIT and may overcome the aforementioned challenges of current therapies. The objective of this narrative review is to summarize the current HIT guidelines, discuss limitations to contemporary treatment options, provide insight into the emerging evidence for the DOACs rivaroxaban, apixaban, and dabigatran, and conclude with a clinical summary for their use in this setting. The PubMed, Google Scholar, and MEDLINE databases were searched for peer-reviewed literature from January 1, 2012, to June 31, 2018. Twenty-seven articles met inclusion criteria for review: 1 prospective trial, 5 retrospective cohort studies, and 21 case reports totaling 104 patients treated with a DOAC for HIT. The DOACs prevented new and recurrent thrombosis in 98% (n=102) of cases, and bleeding complications occurred in 3% (n=3). While current literature remains limited, it is suggestive of a potential role of DOACs for HIT, which has led to their integration into the 2018 American Society Hematology Guidelines with a conditional recommendation.

Study Objectives. To evaluate steady-state bivalirudin dosing requirements in patients with a wide range of kidney function who were being treated for heparin-induced thrombocytopenia (HIT)-related disorders. Design. Retrospective medical record review. Setting. Academic medical center. Patients. Sixty-four adults with varying degrees of renal function who were receiving bivalirudin for at least 48 hours for HIT-related disorders between March 2007 and May 2010. Measurements and Main Results. Steady-state conditions were defined as a constant bivalirudin infusion dose for at least 12 hours, with serum creatinine concentration varying less than 20% for 48 hours (for patients not receiving renal replacement therapy) and at least two therapeutic activated partial thromboplastin time (aPTT) values (60–80 sec). Patients were assigned to five groups based on Cockcroft-Gault-estimated creatinine clearance (Clcr) of less than 30, 30–60, or greater than 60 ml/minute, or by type of renal replacement therapy—intermittent hemodialysis or continuous venovenous hemofiltration (CVVH). For Clcr greater than 60 ml/minute, the median bivalirudin dose was 0.15 mg/kg/hour (interquartile range [IQR] 0.11–0.15 mg/kg/hr), which was greater than median doses for Clcr 30–60 ml/minute (0.10 mg/kg/hr, IQR 0.06–0.13 mg/kg/hr, p=0.004), Clcr less than 30 ml/minute (0.08 mg/kg/hr, IQR 0.04–0.1 mg/kg/hr, p=0.001), CVVH (0.06 mg/kg/hr, IQR 0.03–0.10 mg/kg/hr, p=0.046), and hemodialysis (0.04 mg/kg/hr, IQR 0.03–0.05 mg/kg/hr, p=0.0001). Bivalirudin doses correlated with Clcr (Spearman r = 0.58, p

Study objectives To compare the effectiveness of bivalirudin and argatroban in achieving anticoagulation goals and to compare clinical outcomes assessing the safety and efficacy in patients with known or suspected heparin-induced thrombocytopenia (HIT). Design Single-center, retrospective analysis. Setting Large tertiary care academic medical center. Patients A total of 138 adults who received either bivalirudin (92 patients) or argatroban (46 patients) for at least 24 hours for known or suspected HIT between January 2007 and July 2008. MEASUREMENTS AND MAIN RESULTS. Data regarding demographics, direct thrombin inhibitor (DTI) dosing and monitoring, and related clinical outcomes were collected; statistical analysis was performed to compare results for patients receiving bivalirudin versus those receiving argatroban. Duration of DTI use ranged from 24-658 hours. At the time of DTI initiation, 108 patients (78%) were in an intensive care unit, with the highest proportion (61/138 [44%]) in the cardiothoracic surgery intensive care unit. The median (interquartile range [IQR]) DTI doses at the time of first reaching therapeutic goal were bivalirudin 0.06 mg/kg/hour (0.04-0.08 mg/kg/hr) and argatroban 1.0 μg/kg/minute (0.5-2.0 μg/kg/min). The median percentage of activated partial thromboplastin time (aPTT) values within therapeutic range while patients were receiving DTI therapy were similar for bivalirudin and argatroban (75% and 70%, respectively, p=0.238). A greater percentage of aPTT values were supratherapeutic with argatroban versus bivalirudin treatment (18% vs 8%, p=0.046). Median time to therapeutic goal was similar for bivalirudin (5.50 hrs [IQR 4-14.5 hrs]) and argatroban (5.75 hrs [IQR 3-17.7 hrs], p=0.499). New thromboembolic events occurred in seven patients (8%) receiving bivalirudin and two (4%) receiving argatroban (p=0.718). Bleeding events occurred at similar rates in both groups (9% for bivalirudin vs 11% for argatroban, p>0.999). Conclusions Bivalirudin and argatroban were similar in achieving and maintaining therapeutic anticoagulation goals, clinical outcomes, and safety. This study suggests that bivalirudin represents an alternative in the management of HIT, but prospective studies are needed.

Study Objective. To evaluate the safety and efficacy of bivalirudin compared with heparin for preventing hemofilter occlusion during continuous venovenous hemofiltration (CVVH). Design. Prospective, randomized, double-blind study. Setting. University-affiliated hospital. Patients. Ten critically ill adults (median age 58 yrs, 70% male) with acute renal failure who, without anticoagulation, experienced hemofilter survival time of 24 hours or less during CVVH. Intervention. Patients were randomized to receive bivalirudin 2 mg/hour (five patients) or heparin 400 units/hour (five patients) administered prefilter into the extracorporeal circuit. Measurements and Main Results. Patients had a median Acute Physiology and Chronic Health Evaluation (APACHE) II score of 24, Sequential Organ Failure Assessment (SOFA) score of 11, and reduced antithrombin activity (75.5 units/dl). Baseline characteristics were not significantly different between groups. Study drug was administered in 40 hemofilters (18 from bivalirudin-treated patients, 22 from heparin-treated patients). The primary efficacy outcome was hemofilter survival time, defined as the interval of time between commencement of CVVH with a new extracorporeal circuit (hemofilter) and hemofilter failure. Compared with no anticoagulation, the addition of bivalirudin or heparin significantly improved hemofilter survival time (mean ± SD 10 ± 5 hrs with no anticoagulation vs 22 ± 18 hrs with anticoagulation, p=0.0005). Hemofilter survival time was significantly increased in patients receiving bivalirudin versus those receiving heparin (29.6 ± 20.7 vs 16.5 ± 13.6 hrs, p=0.045). Independent predictors of hemofilter survival were use of bivalirudin therapy and increased antithrombin III activity. No patients randomized to bivalirudin experienced any bleeding or thrombosis events; one patient who received heparin developed alveolar hemorrhage, and one developed a lower extremity deep vein thrombosis. Conclusion. Compared with heparin, bivalirudin was more efficacious in prolonging hemofilter survival time and was well tolerated. Additional studies of bivalirudin for prevention of hemofilter occlusion during continuous renal replacement therapy are warranted.

The temporary total artificial heart (TAH-t) has emerged as an effective bridge to transplantation for individuals with biventricular failure. Implantation of a TAH-t creates a hypercoagulable state requiring a multidrug approach that includes low-dose unfractionated heparin (UFH) in order to minimize thromboembolism. A concern with UFH is the development of heparin-dependent antibodies, which develop in up to 50% of patients receiving the drug as part of cardiopulmonary bypass. If UFH therapy continues postoperatively, the risk of heparin-induced thrombocytopenia approaches 3%. Small investigations have demonstrated that bivalirudin, given as a bolus of 0.75-1 mg/kg followed by an infusion at 1.75-2.5 mg/kg/hour, is an effective alternative to UFH for therapeutic anticoagulation during coronary artery bypass surgery, valve replacement, or both. We describe a series of five adults (age range 24-58 yrs) who received bivalirudin as an alternative to low-dose UFH after TAH-t implantation. None of the patients had documented heparin-induced thrombocytopenia. Treatment was started at the discretion of the treating physician, and adjustments were based principally on the results of thromboelastography. Additional general monitoring included activated partial thromboplastin time, prothrombin time, international normalized ratio, fibrinogen, D-dimer, platelet count, hemoglobin, hematocrit, and platelet aggregation studies. Bivalirudin therapy was continued until successful warfarin implementation. All five patients received bivalirudin in addition to standard antithrombotic therapy. Bivalirudin treatment started at a dosage of 0.005 or 0.01 mg/kg/hour with titration to maintain normocoagulability, which occurred (without concomitant warfarin therapy) within the dosage range of 0.01-0.02 mg/kg/hour. Duration of TAH-t implantation was a mean of 38.8 days (range 25-60 days), and bivalirudin was continued for a mean of 15.2 days (range 7-24 days). No major hemorrhagic events occurred during treatment, and all patients successfully transitioned to warfarin therapy. Low-dose bivalirudin, as an alternative to UFH, maintained normocoagulability after TAH-t implantation. Further investigation is warranted to define the role and dosing of bivalirudin in this situation.

Heparin-induced thrombocytopenia (HIT) is an immune-mediated complication that can occur after exposure to heparin products. Because patients with HIT are at increased risk for thrombosis, anticoagulation is warranted. The direct thrombin inhibitors lepirudin and argatroban are approved by the United States Food and Drug Administration (FDA) for this indication. Bivalirudin, another direct thrombin inhibitor, is approved for use in patients with HIT who must undergo percutaneous coronary intervention. The synthetic pentasaccharide fondaparinux lacks FDA approval for treating patients with HIT; however, a few published reports describe its use. Furthermore, various small-scale, in vitro studies have demonstrated a lack of cross-reactivity between fondaparinux and HIT antibodies. Large, in vivo comparison trials must be performed before fondaparinux can become a standard treatment option in the setting of HIT.

The recognition and management of heparin-induced thrombocytopenia (HIT) and heparin-induced thrombocytopenia with thrombosis syndrome (HITTS) has been evolving over the past several years. Although HIT is a relatively uncommon adverse event in patients receiving heparin therapy, it bears a significant risk of thrombotic events. If patients are left untreated, 50% can develop thrombosis. Several direct thrombin inhibitors have been studied as alternative anticoagulants in patients with HIT. Lepirudin and argatroban are both approved by the United States Food and Drug Administration (FDA) for the management of HIT. Lepirudin requires dosage adjustments in patients with renal insufficiency and has potential for antibody formation. Argatroban requires dosage adjustments in patients with hepatic insufficiency. Argatroban increases the international normalized ratio when coadministered with warfarin, leading to dosage difficulties when transitioning to warfarin therapy. Bivalirudin is the most recent direct thrombin inhibitor to be introduced to the market, but it is not currently FDA approved for HIT. Controversy still exists over which direct thrombin inhibitor to use, especially in acutely ill patients and in those requiring invasive or surgical procedures. Bivalirudin has a relatively short half-life and a predictable response, which makes it attractive as an anticoagulant in patients requiring invasive or surgical procedures, those who are acutely ill, or patients with both renal and hepatic insufficiency. It offers promise as an additional direct thrombin inhibitor for use in patients with HIT, but additional studies need to be performed to further define its use.

Acute coronary syndromes (ACS) consist of unstable angina (UA), non-ST-segment myocardial infarction (NSTEMI) and ST-segment myocardial infarction (STEMI). Timely intervention with effective, predictable antithrombin therapy is critically important in the early management of these conditions. Platelet aggregation is also an important component of thrombus formation in arterial thrombosis. Historically, unfractionated heparin (UFH) has been combined with aspirin to suppress thrombin propagation and fibrin formation; however, its effectiveness has been questioned in this setting. Unlike newer anticoagulant alternatives, UFH paradoxically stimulates platelet aggregation, which may further promote clot formation. In addition, obtaining a valid therapeutic activated partial thromboplastin time (aPTT) in cardiology patients is a major challenge, and dosing is complex. Due to substantial variation in reagents and instruments, target aPTT ranges for UFH in ACS clinical trials cannot be extrapolated to individual institutions. Further, the risk of ischemic events is greater shortly after abrupt discontinuation of UFH compared with alternative agents with longer half-lives and less stimulation of platelet aggregation. Key UA-NSTEMI clinical trials have demonstrated that UFH is inferior to newer agents, such as the low-molecular-weight heparins (LMWHs). Consistent with this evidence, the most recent practice guidelines of the American College of Cardiology and the American Heart Association in UA-NSTEMI identify the LMWH enoxaparin as the agent of choice. In patients with STEMI receiving the fibrinolytic tenecteplase as reperfusion therapy, enoxaparin has also been superior to UFH in combination. In percutaneous procedures, newer indirect (enoxaparin) and direct (bivalirudin) antithrombins have demonstrated safety and efficacy. There is little doubt that as we move forward in optimizing adjunctive anticoagulation in the cardiology setting, UFH will largely be replaced by better antithrombin agents.

Despite advances in percutaneous coronary intervention (PCI) techniques and adjunctive therapies, the risks of ischemic and bleeding complications with PCI remain significant. These complications are associated with significant morbidity and mortality, as well as substantially higher costs. Bivalirudin is the only antithrombotic agent that has been shown to reduce both ischemic and hemorrhagic complications associated with PCI. Cost models drawn from the results of three clinical trials of bivalirudin have estimated its potential impact on total medical costs. In addition, the number needed to treat to avoid a bleeding complication has been calculated based on patients shown to have a heightened risk of bleeding in the Bivalirudin Angioplasty Trial. In all models assessed, the use of bivalirudin offset most of its own cost through reductions in bleeding and ischemic complications.

Study objectives To compare dosing strategies using total body weight (actual measured body weight), adjusted body weight, and ideal body weight when starting bivalirudin for the treatment for heparin-induced thrombocytopenia (HIT) in obese patients, and to compare differences in dosing requirements and clinical outcomes between obese and nonobese patients. Design Retrospective medical record review. Setting Academic tertiary care medical center. Patients One hundred thirty-five medical and surgical patients who were treated with bivalirudin for HIT between June 1, 2004, and October 1, 2009. Measurements and main results The 135 patients were separated into two groups based on body mass index (BMI): 46 patients had a BMI greater than 30 kg/m(2) and were classified in the obese group; the nonobese group consisted of 89 patients with a BMI less than 30 kg/m(2) . The mean BMI in the obese group was 37.7 kg/m(2) (range: 30.1-56.2 kg/m(2) ). Weight-standardized doses that achieved activated partial thromboplastin time (aPTT) goal were compared in the obese group. The mean ± SD doses that achieved aPTT goal with total (actual), adjusted, and ideal body weights in this group were 0.1 ± 0.07, 0.11 ± 0.08, and 0.14 ± 0.09 mg/kg/hour, respectively. Of the three weight-based dosing approaches, total body weight followed by adjusted body weight provided the closest correlation to rates observed at the target aPTT goal. The secondary analysis compared initial doses of bivalirudin, doses required to reach goal aPTT, time to achieve goal aPTT, and clinical outcomes (number of patients not achieving goal, new thrombosis, major bleeding, and 30-day all-cause mortality) between the obese and nonobese groups. A significant difference in initial dose was noted between groups; however, no significant differences in dose required to achieve goal aPTT, time to achieve goal aPTT, and clinical outcomes were noted between the obese and nonobese groups. Conclusion This study provides evidence that the dosing strategy for bivalirudin based on total body weight is the most accurate predictor of achieving aPTT goal in obese patients with HIT. The study also suggests that there are no clinical differences that warrant different dosing strategies between obese and nonobese patients. Further prospective studies are needed to confirm these findings.

Current guidelines recommend using bivalirudin, a direct thrombin inhibitor,as a preferred alternative to unfractionated heparin in patients with heparin induced thrombocytopenia (HIT) for percutaneous coronary intervention, as well as for cardiac and vascular surgery. Anticoagulation during radiofrequency catheter ablation (RFA) procedures may be another potential use for bivalirudin in the setting of HIT. Radiofrequency catheter ablation procedures involving left atrial or left ventricular access are increasingly employed as a method to treat cardiac arrhythmias. Because stroke risk is a serious complication of RFA, anticoagulation is required during this procedure. We describe the first report, to our knowledge, of successful use of bivalirudin anticoagulation during RFA procedures in two patients with a history of clinically diagnosed HIT that precluded the use of unfractionated heparin or low-molecular-weight heparin. One of the patients underwent RFA for ventricular tachycardia, the other for pulmonary vein isolation for the treatment of atrial fibrillation. In both patients, bivalirudin was administered as a 0.75-mg/kg intravenous bolus, followed by a 1.75-mg/kg/hour infusion.Activated clotting time (ACT) was measured after the initial bolus in each patient. However, no dosage adjustment was made based on the ACT, and the infusion rate of bivalirudin remained fixed during the procedures. Both procedures were completed without any embolic events. No bleeding or clotting events were noted; one patient experienced minor access site oozing that was not felt to be clinically important. Bivalirudin is a therapeutic option for anticoagulation during left-sided catheter RFA procedures in patients with a history of HIT.

Direct thrombin inhibitors are commonly used anticoagulants in patients with known or suspected heparin-induced thrombocytopenia (HIT). All three direct thrombin inhibitors available in the United States-argatroban, bivalirudin, and lepirudin-are pregnancy category B drugs based on animal studies, but little data are available on the safety of these agents during human pregnancy. Whereas several case reports support the safe use of lepirudin, only one case report has been published with argatroban and none with bivalirudin. We describe a 26-year-old pregnant woman with portal vein thrombosis and thrombocytopenia treated with argatroban for possible HIT during her last trimester. An argatroban infusion was started at 2 microg/kg/minute during her 33rd week of pregnancy, with the dosage titrated based on the activated partial thromboplastin time; infusion rates ranged from 2-8 microg/kg/minute. Treatment continued until her 39th week of pregnancy, when labor was induced. Argatroban therapy was discontinued 7 hours before epidural anesthesia. The patient successfully delivered a healthy male newborn, devoid of any known adverse effects from argatroban. The infant was found to have a small ventricular septal defect and patent foramen ovale at birth, but it is unlikely that these were caused by argatroban since organogenesis occurs in the first trimester. Even though the cause of this patient's thrombocytopenia was later determined to be idiopathic thrombocytopenic purpura, this is an important case that adds to the literature on use of argatroban during pregnancy.

Objective. To compare clinical outcomes and glycoprotein IIb-IIIa inhibitor use in patients undergoing percutaneous coronary intervention (PCI) who received bivalirudin or unfractionated heparin (UFH) in a real-world setting. Design. Retrospective cohort analysis. Setting. University-affiliated medical center. Patients. One thousand seventy-five adult patients who underwent PCI and received either bivalirudin (539 patients) or UFH (536 patients) from April 1, 2003–April 1, 2004. Measurement and Main Results. Patient data on demographics, comorbidities, laboratory values, and reports of radiologic examinations, cardiac catheterizations, and discharge summaries were obtained. Outcomes evaluated included rates of in-hospital mortality, myocardial infarction, revascularization, and length of stay (LOS), as well as Randomized Evaluation of PCI Linking Angiomax to Reduced Clinical Events (REPLACE-2) and Thrombosis in Myocardial Infarction (TIMI) bleeding categorization. Bivalirudin use was associated with a significant reduction in TIMI major (5.0% vs 9.7%, p=0.003), REPLACE-2 major (5.4% vs 12.9%, p

Heparin-induced thrombocytopenia (HIT) is an immune-mediated adverse effect that typically manifests several days after the start of heparin therapy, although both rapid- and delayed-onset HIT have been described. Its most serious complication is thrombosis. Although not all patients develop thrombosis, it can be life threatening. The risk of developing HIT is related to many factors, including the type of heparin product administered, route of administration, duration of therapy, patient population, and previous exposure to heparin. The diagnosis of HIT is typically based on clinical presentation, exposure to heparin, and presence of thrombocytopenia with or without thrombosis. Antigen and activation laboratory assays are available to support the diagnosis of HIT. However, because of the limited sensitivity and specificity of these assays, bedside probability scales for HIT were developed. When HIT is suspected, prompt cessation of all heparin therapy is necessary, along with initiation of alternative anticoagulant therapy. Two direct thrombin inhibitors--argatroban and lepirudin--are approved for the management of HIT in the United States, and bivalirudin is approved for use in patients with HIT who are undergoing percutaneous coronary intervention. Other agents, although not approved to manage HIT, have also been used; however, their role in therapy requires further evaluation. A comprehensive HIT management strategy involves the evaluation of numerous factors. Many patients, including those undergoing coronary artery bypass surgery, those with acute coronary syndromes, those with hepatic or renal insufficiency, and children, require special attention. Clinicians must become familiar with the available information on this serious adverse effect and its treatment so that optimum patient management strategies may be formulated.

Study Objective. To perform a cost-effectiveness analysis comparing three treatment approaches during nonurgent percutaneous coronary intervention (PCI): bivalirudin with provisional glycoprotein (GP) IIb-IIIa inhibitor therapy, unfractionated heparin (UFH) with eptifibatide, and UFH with abciximab. Design. Literature-based decision model from an institutional perspective. Data Source. Patient data from the Randomized Evaluation in PCI Linking Angiomax to Reduced Clinical Events (REPLACE)-2 study and three other randomized controlled trials that included UFH and routine GP IIb-IIIa inhibitor (eptifibatide or abciximab) therapy. All included studies were comparable based on patient population, procedural techniques, and general treatment approaches. Measurements and Main Results. We included patient populations undergoing contemporary nonurgent PCI to identify probabilities of success or complications (myocardial infarction, urgent revascularization, thrombocytopenia, and major or minor bleeding at 30 days). Costs were assigned to each outcome by incorporating diagnosis-related group- and/or Current Procedural Terminology-associated costs, institutional drug acquisition costs, and unit replacement costs of platelets and red blood cells. In the base-case analysis, the use of bivalirudin with provisional GP IIb-IIIa inhibitor therapy dominated the UFH and planned GP IIb-IIIa inhibitor approach: UFH with eptifibatide was $74 more expensive and 1.2% less effective, and UFH with abciximab was $777 more expensive and 2.3% less effective. Sensitivity analyses indicated that the model results were robust, but also revealed that bivalirudin lost its cost-effectiveness, resulting in UFH with eptifibatide becoming more cost-effective, when two or more vials of bivalirudin were necessary in greater than 27% of cases or when the use of provisional GP IIb-IIIa inhibitor therapy exceeded 20%. Conclusion. This analysis indicates that bivalirudin with provisional GP IIb-IIIa inhibitor therapy is the most cost-effective antithrombotic treatment strategy in nonurgent PCI when its use and dosing are consistent with the REPLACE-2 trial.

Study Objective. To evaluate the efficacy, safety, and associated costs of anticoagulation with argatroban, bivalirudin, and lepirudin for managing patients with heparin-induced thrombocytopenia (HIT) or presumed HIT. Design. Retrospective medical record review. Setting. University-affiliated teaching hospital. Patients. Forty-two patients who were hospitalized between January 1 and December 31, 2004, and who were treated with bivalirudin, argatroban, or lepirudin for at least 24 hours. Measurements and Main Results. The primary outcome was the time to reach the desired goal for activated partial thromboplastin time (aPTT). Secondary outcomes were the number of aPTT measurements within the therapeutic range, costs, treatment duration, clinical outcomes, and adverse events. Of the 42 patients who met the inclusion criteria, 24 received bivalirudin, 13 received argatroban, and 5 received lepirudin. Patients receiving bivalirudin who reached therapeutic aPTTs attained them sooner than those receiving either argatroban or lepirudin (8.5 vs 14 and 24 hrs, respectively, p=0.124). Average percentage of therapeutic aPTTs/patient was greatest in the argatroban group (62%), followed by the bivalirudin (57%) and lepirudin (29%) groups (p=0.062). Average drug cost/day/patient was greater in the lepirudin group than the other groups, whereas average laboratory costs were similar among groups. Treatment duration was longer with argatroban than with bivalirudin or lepirudin. Bleeding rates were similar in the argatroban and bivalirudin groups, but higher than in the lepirudin group. A composite of clinical outcomes (deep vein thrombosis, nonfatal myocardial infarction, nonfatal stroke, limb amputation, and all-cause mortality) were similar among the three groups. Conclusion. All three drugs were effective as anticoagulants for patients with HIT or presumed HIT. Based on average use and average wholesale price, bivalirudin cost less per day than the other two agents. Although not yet approved by the United States Food and Drug Administration for management of HIT, bivalirudin appears to be a viable treatment alternative for anticoagulation therapy.

The treatment of patients with acute coronary syndromes has changed dramatically over the last several years. Most patients now undergo some form of percutaneous coronary intervention (PCI), which includes either stent placement or percutaneous transluminal coronary angioplasty (PTCA). Along with new medical interventions for acute coronary syndromes comes the need for new antithrombotic therapies. Combination therapy with antiplatelet agents (aspirin, adenosine diphosphate inhibitors), glycoprotein (GP) IIb-IIIa receptor inhibitors, and anticoagulants (unfractionated heparin or low-molecular-weight heparins) is administered, depending on the type of intervention and severity of the coronary lesion. Bivalirudin is a direct thrombin inhibitor that recently was approved as an alternative to heparin in patients undergoing PTCA. Compared with unfractionated heparin, bivalirudin reduces the rate of death, myocardial infarction, or revascularization, with a concurrent reduction in bleeding. This agent offers promise as a replacement for unfractionated heparin in PCI and is being studied in comparison with unfractionated heparin plus GP IIb-IIIa receptor inhibitors in patients undergoing intracoronary stent placement.

Acute coronary syndromes encompass a spectrum of conditions, including myocardial infarction and unstable angina. These syndromes are related to the formation and disruption of atherosclerotic plaque. Rupture of plaque leads to thrombin generation, fibrin deposition, and platelet aggregation, ultimately resulting in restriction of blood flow and ischemia of cardiac tissue. Percutaneous coronary intervention (PCI), including angioplasty and coronary stent placement, has been developed to open occluded arteries. The frequency with which these procedures are performed speaks to their largely successful outcomes. However, the mechanical manipulations of PCI result in additional plaque rupture and damage to the vessel wall, exposing subendothelial components to blood and resulting in the initiation of the clotting cascade and in platelet activation. Left unchecked, these intertwined processes lead to formation of arterial thrombi at the site of endothelial damage, and potentially to abrupt vessel closure or embolization of thrombi into the distal microcirculation. Thrombin plays a central role in thrombus formation and platelet activation, and its inhibition significantly reduces thrombus-related sequelae. Current antithrombotic strategies during PCI are based on the traditional indirect thrombin inhibitor heparin. Heparin has several limitations in efficacy and safety, due in part to its indirect mechanism of action. Bivalirudin, a direct thrombin inhibitor, offers significant improvement over heparin in the clinical outcomes and risks associated with PCI.

In a large phase III study of patients with unstable angina treated with percutaneous transluminal coronary angioplasty (PTCA), the thrombin-specific anticoagulant bivalirudin produced relative risk reductions of 22% (p = 0.039) for ischemic complications and 62% (p < 0.001) for bleeding complications compared with heparin. Subsequent reports have shown that between-treatment differences favoring fewer complications with bivalirudin also extend to high-risk patients. Early heparinization promotes heparin resistance and decreases activated clotting time achieved during PTCA. These effects are relevant to patients with postinfarction angina, which is associated with a greater likelihood of early vessel closure and procedural failure. In 1006 patients with one or both of these risk factors, bivalirudin significantly reduced combined ischemic and bleeding complications compared with heparin (8.6% vs 18%, p < 0.001). Treatment separations favoring bivalirudin increased with risk, suggesting decreased heparin effectiveness in patients at heightened risk. Findings in three additional risk groups-women, the elderly, and patients not receiving glycoprotein IIb/IIIa inhibitors-also showed fewer complications with bivalirudin therapy. Preliminary data suggest that bivalirudin can be combined safely with glycoprotein IIb/Illa antagonists in percutaneous coronary intervention (PCI), including PTCA. An ongoing trial is aimed at determining the efficacy and safety of heparin with planned glycoprotein IIb/IIIa therapy versus bivalirudin with provisional glycoprotein IIb/IIIa therapy. The use of bivalirudin in patients with heparin-induced thrombocytopenia also is being evaluated after favorable findings in early compassionate-use studies. The fact that between-treatment differences favoring bivalirudin were especially outstanding among the high-risk patients considered in this review reinforces the impression that bivalirudin is a promising and unprecedented alternative to heparin in PCI.

Much progress has been made in understanding and treating acute coronary syndromes. For patients undergoing percutaneous transluminal coronary angioplasty, anticoagulant therapy during the procedure must strike a balance between providing sufficient anticoagulation to prevent thrombus formation and ischemic complications while averting hemorrhagic complications. Bivalirudin, a thrombin-specific anticoagulant, is the only anticoagulant that reduces both ischemic and bleeding complications associated with percutaneous coronary intervention (PCI). Bivalirudin is easy to use, provides predictable anticoagulation, inactivates both free and clot-bound thrombin, and blocks thrombin-mediated platelet activation and aggregation. Drug-drug interaction studies have found no clinically relevant interactions between bivalirudin and ticlopidine, abciximab, tirofiban, or eptifibatide. Bivalirudin is well tolerated by patients who previously received low-molecular-weight heparin (LMWH), when LMWH is discontinued 8-14 hours before bivalirudin is started. Similarly, switching from heparin to bivalirudin at the time of PCI reduces both ischemic and bleeding events.