Clinical imaging in anti-atherosclerosis drug development.

The development of novel drugs for the treatment of atherosclerosis faces many challenges, particularly caused by the need for large and costly outcome trials. When predictive biochemical biomarkers are not available, clinical imaging data can serve as intermediate Phase II endpoints to demonstrate mechanistic and anti-atherosclerotic activity of new compounds. These data can support risk mitigation before continuing development in large Phase III outcome trials. Imaging techniques such as magnetic resonance imaging (MRI), computed tomography (CT) and ultrasound [intima-media thickness (IMT) and intravascular ultrasound (IVUS)] can provide detailed information on vascular plaque volume and morphology, whereas functional changes can potentially be captured by positron emission tomography (PET) techniques in the vessel wall. We will review the application and operational aspects of clinical imaging methods and endpoints used in interventional atherosclerosis trials.

Sustained heparin effect contributes to reduced plasma thrombin generation capacity early after cardiac surgery.

INTRODUCTION: Thrombin is a key component in the coagulation cascade, and impaired thrombin generation has been linked to increased bleeding after surgical procedures. The aim was to evaluate postoperative thrombin generation capacity in plasma after cardiac surgery, and its potential associations to activity of individual coagulation factors and heparin. MATERIAL AND METHODS: Forty-eight coronary artery bypass grafting patients were included in a prospective observational cohort study. Thrombin generation capacity was analysed in plasma with calibrated automated thrombogram with tissue factor as activator before (baseline), and 2 h and 24 h after surgery. In addition, plasma activity of coagulation factors II, V, VII, VIII, IX, X, XI, XIII, were determined. Heparin effect was assessed by anti-Xa activity, APTT and thrombin time. RESULTS: Thrombin generation was markedly reduced 2h after surgery compared to baseline. Peak levels decreased with median 74% (interquartile range 52-90), p<0.001, and endogenous thrombin generation potential decreased with 65% (43-86), p<0.001. Postoperative changes in endogenous thrombin generation potential correlated inversely to changes in anti-Xa activity (r=-0.51, p=0.010) and to changes in thrombin time (r=-0.51, p=0.009), but there were no correlations to changes in individual coagulation factor activity. CONCLUSIONS: A marked reduction in thrombin generation potential was observed in the early postoperative phase after cardiac surgery. The decrease was independent of reductions in individual coagulation factor activity but correlated to heparin effects. The results indicate that a sustained heparin effect contributes to the postoperative reduction in thrombin generation capacity.

Oral direct thrombin inhibitor AZD0837 for the prevention of stroke and systemic embolism in patients with non-valvular atrial fibrillation: a Phase II study of AZD0837 in patients who are appropriate for but unable or unwilling to take vitamin K antagonist therapy.

BACKGROUND: Some patients with atrial fibrillation (AF) cannot be treated with vitamin K antagonists (VKAs) and will therefore not receive effective thromboprophylaxis. The primary objective of the present Phase II trial (NCT00623779) was to assess the feasibility of conducting a study with a novel oral anticoagulant, the direct thrombin inhibitor AZD0837, in patients with AF unable or unwilling to take warfarin, by evaluation of dropout rates and compliance. METHODS: Patients were randomised to receive AZD0837 extended-release tablets 150 mg (n=43) or 300 mg (n = 42) once daily, or standard therapy (no treatment, aspirin 75-325 mg or clopidogrel 75 mg once daily; n = 46) for a median treatment duration of 6 weeks. RESULTS: Reasons for patients not being treated with warfarin were: refusal or permanent cessation decided by the patient (64.8%), inability to keep international normalised ratio 2-3 over a 3-month period (23.2%), physician assessment that VKA was inappropriate (20.4%) and warfarin allergy (2.8%). Compliance with treatment (mean ± SD) was 97.0 ± 16.5% for AZD0837 150 mg and 99.8 ± 1.4% for 300 mg. Compliance with study visits was high (mean 93-98%). The numbers of dropouts were four, six and three, whilst minor or clinically significant minor bleeds were reported in zero, five and two patients in the AZD0837 150 mg, 300 mg and standard-therapy groups, respectively. No major bleeds were reported. Both doses of AZD0837 reduced levels of fibrin D-dimer and prolonged activated partial thromboplastin time, ecarin clotting time and thrombin clotting time. CONCLUSIONS: AZD0837 had a good safety profile during this study, including a low incidence of bleeding events, with effective anticoagulation on pharmacodynamic parameters. A larger study in AF patients unable or unwilling to take warfarin is feasible, as judged by compliance and dropout rates.

Plasma activity of individual coagulation factors, hemodilution and blood loss after cardiac surgery: a prospective observational study.

BACKGROUND: Hemodilution and consumption of coagulation factors during cardiopulmonary bypass has been suggested to contribute to bleeding complications after cardiac surgery. The aim was to describe the activity of individual coagulation factors after CABG in relation to hemodilution and postoperative bleeding. MATERIALS AND METHODS: Plasma concentrations of fibrinogen and plasma activity of FII, FV, FVII, FVIII, FIX, FX, FXI and FXIII adjusted for hemodilution were analysed in 57 CABG patients before, and 2h and 24h after surgery. Postoperative bleeding was registered and correlations to coagulation factor activity were calculated. RESULTS: Adjusted plasma concentration of fibrinogen (-14+/-6%), and plasma activity of FII (-9+/-6%), FV (-13+/-8%), FX (-13+/-7%) and FXIII (-9+/-14%) were reduced two hours after surgery compared to baseline (all p<0.001). FVII (+3+/-12%, p=0.34) and FXI (+1+/-19%, p=0.50) were unchanged, while FVIII (+23+/-44%, p=0.006) and FIX (+23+/-17%, p<0.001) increased. Twenty-four hours after surgery fibrinogen (+45+/-27%), FVIII (+93+/-66%) and FIX (+33+/-26%) were all increased (all p<0.001), while FVII (-37+/-14%, p<0.001), FXI (-4+/-18%, p=0.02) and FXIII (-6+/-15%, p=0.004) were decreased. Median postoperative blood loss was 380 ml/12h. There were significant inverse correlations between postoperative blood loss and fibrinogen concentration 2h after surgery (r=-0.33, p=0.019) and between postoperative blood loss and pre- and postoperative FXIII activity (r=-0.34, p=0.009 and r=-0.41, p=0.003, respectively), but not between blood loss and any of the other factors. CONCLUSIONS: There is a marked dissociation in plasma activity of individual coagulation factors after CABG. Plasma concentration of fibrinogen and factor XIII activity correlates inversely to postoperative blood loss after CABG.

Effect of ximelagatran on ischemic events and death in patients with atrial fibrillation after acute myocardial infarction in the efficacy and safety of the oral direct thrombin inhibitor ximelagatran in patients with recent myocardial damage (ESTEEM) trial.

BACKGROUND: New-onset trial fibrillation (AF) occurs commonly after acute myocardial infarction (MI) and is associated with a poor prognosis due to stroke or death. The optimal antithrombotic therapy is unknown. The aim of this study was to investigate whether an oral direct thrombin inhibitor, ximelagatran, added to aspirin, reduced the risk of death, myocardial infarction (MI), and stroke in patients who developed AF after their qualifying MI in the efficacy and safety of the oral direct thrombin inhibitor ximelagatran in patients with recent myocardial damage (ESTEEM) trial. METHODS: The ESTEEM trial evaluated 6 months treatment with ximelagatran together with aspirin, compared to aspirin alone, for prevention of ischemic events in 1883 patients randomized within 14 days after an MI. After their qualifying MI, 174 (9%) patients developed AF in hospital. Multivariate hazard ratios for ximelagatran compared with placebo were calculated by presence AF. RESULTS: Of 101 patients with AF treated with ximelagatran 7 (6.9%) had either death, MI, or stroke, compared with 15 (20.6%) in 73 patients allocated to placebo. Ximelagatran reduced the risk of death, MI, or stroke by 70% (hazard ratio 0.30, 95% CI 0.12-0.74). For the separate outcome events, we found similar, nonsignificant trends. One major bleeding event occurred in each treatment group. CONCLUSIONS: For patients with MI complicated by AF, the combination of aspirin and an oral direct thrombin inhibitor seems beneficial. The high risk for death, MI, and stroke in this population and the increasing use of percutaneous interventions in MI patients may suggest a combination of long-term antiplatelet and anticoagulant therapy. Randomized clinical trials are warranted.

Early decrease in coagulation activity after myocardial infarction is associated with lower risk of new ischaemic events: observations from the ESTEEM Trial.

AIM: Patients with a recent myocardial infarction have an increased risk of recurrent ischaemic events. In the ESTEEM trial, the oral direct thrombin inhibitor ximelagatran reduced the risk of new ischaemic events when compared with placebo in aspirin treated post myocardial infarction patients. Ximelagatran persistently reduced markers of coagulation activity, i.e. prothrombin fragment 1 + 2 (F1 + 2) and D-dimer levels. The aim of this substudy was to evaluate the levels of these markers and activated thromboplastin time (APTT) in relation to new ischaemic events or bleeding. METHODS AND RESULTS: In the substudy, 518 out of 1883 patients were included and within 14 days after a myocardial infarction randomized to ximelagatran or placebo for 6 months. The clinical endpoints death, myocardial infarction, severe recurrent ischaemia, ischaemic stroke, and bleeding were evaluated. The levels of F1 + 2, D-dimer, and APTT were analysed at randomization and in serial samples during the study. Ximelagatran treatment appeared to have a larger treatment effect in patients with F1 + 2 and D-dimer levels above the median at randomization with a reduction of ischaemic events from 18 to 9% (P = 0.03) for F1 + 2 and from 20 to 9% for D-dimer (P = 0.009). A reduction of D-dimer levels was found in 60% of the patients 1 week after randomization and these patients had less ischaemic events when compared with patients with unchanged or increased levels (P = 0.03) regardless of treatment. F1 + 2 and D-dimer levels were unrelated to bleeding risk. In the ximelagatran group, increased APTT was not related to ischaemic events but associated with a raised risk of bleeding. CONCLUSION: A reduction of initially high coagulation activity, as measured by the D-dimer level, in patients with recent myocardial infarction identifies patients with a decreased risk of new ischaemic events, regardless whether the reduction occurs spontaneously or is induced by pharmacological means. Patients with higher initial coagulation activity seemed to benefit most from long-term treatment with ximelagatran.

Antithrombotic effects of ximelagatran plus acetylsalicylic acid (ASA) and clopidogrel plus ASA in a human ex vivo arterial thrombosis model.

It was the objective of this study to compare the antithrombotic effects and bleeding profiles of the oral direct thrombin inhibitor ximelagatran, an anticoagulant, and the antiplatelet agent clopidogrel on top of steady-state acetylsalicylic acid (ASA) in a human arterial thrombosis model. Healthy male volunteers (n=62) received ASA (160 mg once daily), plus either clopidogrel for 6 days (loading dose 300 mg, then 75 mg once daily), or a single dose of ximelagatran (36 or 72 mg) on Day 6. Changes in total thrombus area (TTA) under low shear rate (LSR; 212 s(-1)) and high shear rate (HSR; 1690 s(-1)) conditions were measured, using the ex vivo Badimon perfusion chamber model pre-dose and 2 and 5 hours after dosing on Day 6, and capillary bleeding times (CBT) were determined. Ximelagatran plus ASA significantly reduced TTA under LSR and HSR, compared with ASA alone. Ximelagatran plus ASA reduced TTA more than clopidogrel plus ASA under LSR after 2 hours (36 mg, P=0.0011; 72 mg, P<0.0001) and 5 hours (72 mg, P=0.0057), and under HSR after 2 and 5 hours (72 mg, P<0.05). Compared with ASA alone, CBT was markedly prolonged by clopidogrel plus ASA (ratio 6.4; P<0.0001) but only slightly by ximelagatran plus ASA (72 mg ximelagatran, ratio 1.4; P=0.0010). Both drug combinations were well tolerated. Oral ximelagatran plus ASA has a greater antithrombotic effect in this human ex vivo thrombosis model and a less pronounced prolongation of bleeding time than clopidogrel plus ASA.

Comparable pharmacokinetics and pharmacodynamics of melagatran in Japanese and caucasian volunteers after oral administration of the direct thrombin inhibitor ximelagatran.

OBJECTIVES: Two studies were conducted to elucidate the pharmacokinetics and pharmacodynamics of melagatran after administration of the oral direct thrombin inhibitor ximelagatran to Caucasian and Japanese volunteers. METHODS: In study 1, with a single-blind, parallel-group design, young Japanese and Caucasian male volunteers were randomised to receive four single escalating oral doses of ximelagatran (12, 24, 36 and 60mg on separate days; n = 27 per ethnic group) or placebo (n = 6 per ethnic group). In study 2, with an open-label design, elderly Japanese male volunteers (n = 12) received three single escalating oral doses of ximelagatran (12, 24 and 36mg on separate days). RESULTS: Regardless of the ethnicity or age of the volunteers, ximelagatran given in single oral doses was rapidly absorbed and bioconverted to melagatran, and the melagatran area under the plasma concentration-time curve (AUC) and peak plasma concentration (C(max)) increased in proportion with the ximelagatran dose, with only small deviations from absolute linearity. Higher melagatran AUC and C(max) were observed in young Japanese volunteers compared with young Caucasian volunteers, and in elderly Japanese volunteers compared with young Japanese volunteers. These results appear to be attributed to weight- and age-related decreases in renal elimination of melagatran rather than to absorption of ximelagatran and formation of melagatran. The pattern of metabolites in plasma and urine was comparable between young Japanese and Caucasian volunteers, and between young and elderly Japanese volunteers. The melagatran plasma concentration-activated partial thromboplastin time (aPTT, an ex vivo coagulation time measurement used to demonstrate inhibition of thrombin) relationship did not differ significantly between young Japanese and Caucasian volunteers or between young and elderly Japanese volunteers. CONCLUSIONS: Ethnicity does not affect the absorption of ximelagatran or the formation of melagatran or the melagatran plasma concentration-aPTT relationship. The elimination of melagatran is correlated with renal function.

Assessment of bleeding after concomitant administration of antiplatelet and anticoagulant agents in lower limb arthroplasty.

In an analysis of the Melagatran Thrombosis Prophylaxis in Orthopedic Surgery (METHRO) III study, we evaluated whether concomitant administration of aspirin (ASA) and non-steroidal anti-inflammatory drugs (NSAIDs) with the direct thrombin inhibitor melagatran/ximelagatran or the low-molecular-weight heparin enoxaparin increased bleeding in patients undergoing major joint surgery. Further objectives were to compare the influence of the timing of initial postoperative administration of melagatran/ximelagatran on bleeding in orthopedic patients receiving ASA/NSAIDs and in comparison with the preoperative administration of enoxaparin. ASA or NSAIDs in conjunction with melagatran/ximelagatran or enoxaparin did not increase bleeding. Bleeding rates were not significantly different, irrespective of the timing of the initial postoperative dose of melagatran/ximelagatran (4-8 vs. 4-12 h) when compared with preoperative (12 h) administration of enoxaparin. Transfusion rates were significantly lower with administration of melagatran/ximelagatran compared with enoxaparin.

Postoperative Melagatran/Ximelagatran for the Prevention of Venous Thromboembolism following Major Elective Orthopaedic Surgery : Effects of Timing of First Dose and Risk Factors for Thromboembolism and Bleeding Complications on Efficacy and Safety.

OBJECTIVES: To examine the influence of timing of postoperative initiation of subcutaneous melagatran followed by oral ximelagatran, and of risk factors for venous thromboembolism (VTE; including deep vein thrombosis [DVT] and pulmonary embolism [PE]) and bleeding complications, on the efficacy and safety of this regimen, compared with preoperative enoxaparin sodium, following total hip replacement (THR) or total knee replacement (TKR) surgery. DESIGN: Statistical analyses of efficacy and safety in subgroups of the METHRO III intention-to-treat population. MAIN OUTCOME MEASURES: Main efficacy outcome measures were major VTE (proximal DVT, PE or VTE-related death) and total VTE (distal or proximal DVT, fatal or non-fatal PE). The main safety outcome measures were blood transfusion, severe bleeding events, blood loss, bleeding-related adverse events and need for reoperation. RESULTS: In the combined THR and TKR population, melagatran initiated 4 - <8 hours postoperatively was non-inferior to enoxaparin sodium with respect to the risks of total VTE (absolute risk reduction [ARR] 0; 95% confidence interval [CI] -4.4, 4.4) and major VTE (ARR -0.63; 95% CI -2.94, 1.67). The rate of major VTE was unaffected by the different risk factors. In the combined THR and TKR population, blood transfusion requirements were lower with melagatran/ximelagatran than enoxaparin sodium (odds ratio 0.83; 95% CI 0.71, 0.96; p = 0.016). CONCLUSIONS: Melagatran/ximelagatran initiated 4 - <8 hours postoperatively provided a comparable level of protection against total and major VTE to preoperative enoxaparin sodium. Major VTE rates and safety were consistent across different patient subgroups. Subcutaneous melagatran followed by fixed-dose oral ximelagatran offers an alternative to the standard European low molecular-weight heparin regimen in a wide range of patients.

Oral ximelagatran for secondary prophylaxis after myocardial infarction: the ESTEEM randomised controlled trial.

BACKGROUND: Despite important advances in treatment, the risk of recurrent ischaemic events is high both early and late after an acute coronary syndrome. We aimed to assess the effectiveness of ximelagatran and acetylsalicylic acid for prevention of death, non-fatal myocardial infarction, and severe recurrent ischaemia after a recent myocardial infarction. METHODS: In this placebo-controlled, double-blind, multicentre, multinational dose-guiding study we assessed 1883 patients who had had recent ST-elevation or non-ST-elevation myocardial infarction. Within 14 days after the index event we randomised the participants in the proportions 1/1/1/1/2 to oral ximelagatran at doses of 24 mg, 36 mg, 48 mg, or 60 mg twice daily, or placebo, respectively for 6 months. All patients received acetylsalicylic acid 160 mg once daily. The primary efficacy outcome was the dose response of ximelagatran by comparison with placebo for the occurrence of all-cause death, non-fatal myocardial infarction, and severe recurrent ischaemia. Analysis was by intention to treat. FINDINGS: Oral ximelagatran significantly reduced the risk for the primary endpoint compared with placebo from 16.3% (102 of 638) to 12.7% (154 of 1245) (hazard ratio 0.76, 95% CI 0.59-0.98, p=0.036) for the combined ximelagatran groups versus placebo. There was no indication of a dose response between the ximelagatran groups. Major bleeding events were rare, 1.8% (23 of 1245) and 0.9% (six of 638) (hazard ratio 1.97, 95% CI 0.80-4.84) in the combined ximelagatran and placebo groups, respectively. We recorded no serious clinically adverse outcomes judged related to the investigational drug. INTERPRETATION: Oral direct thrombin inhibition with ximelagatran and acetylsalicylic acid is more effective than acetylsalicylic acid alone in preventing major cardiovascular events during 6 months of treatment in patients who have had a recent myocardial infarction.

Ximelagatran and melagatran compared with dalteparin for prevention of venous thromboembolism after total hip or knee replacement: the METHRO II randomised trial.

BACKGROUND: Heparins substantially reduce the risk of thromboembolic complications after total hip or knee replacement. However, they can be given only by injection and have several other drawbacks. We did a multicentre, randomised, double-blind study to examine the dose-response relation of subcutaneous melagatran, a direct thrombin inhibitor, followed by oral ximelagatran as thromboprophylaxis after total hip or knee replacement. We aimed to compare the efficacy and safety with that of dalteparin. METHODS: Of 1900 patients, 1495 were assigned to four dose categories of subcutaneous melagatran from just before surgery (1.00 mg, 1.50 mg, 2.25 mg, or 3.00 mg twice daily) followed from the day after surgery by oral ximelagatran (8 mg, 12 mg, 18 mg, or 24 mg twice daily). 381 patients were assigned subcutaneous dalteparin 5000 IU once daily, from the evening before surgery. Bilateral venography was done at 7-10 days, and clinically suspected venous thromboembolism (VTE) was confirmed radiologically. The primary endpoint was the rate of deep-vein thrombosis and pulmonary embolism (PE). Analyses were by intention to treat. FINDINGS: 1876 patients underwent total replacement of hip (n=1270) or knee (n=606); evaluable venograms were obtained in 1473 (79%). Four patients without evaluable venograms had PE. Overall, a significant dose-dependent decrease in VTE was seen with melagatran/ximelagatran (lowest to highest group: 111 [37.8%], 70 [24.1%], 71 [23.7%], and 43 [15.1%]; p=0.0001); there were also significant relations for both total hip and total knee replacement individually. The frequency of VTE was significantly lower with the highest dose of melagatran/ximelagatran than with dalteparin (15.1% vs 28.2%, p<0.0001). There were no reoperations due to bleeding and no critical organ bleeding. Excessive surgical bleeding was uncommon but more frequent in the highest dose group. INTERPRETATION: This sequential therapy was effective and safe in patients undergoing major joint replacement surgery. The findings should be confirmed in a large phase III trial.

A dose-ranging study of the oral direct thrombin inhibitor, ximelagatran, and its subcutaneous form, melagatran, compared with dalteparin in the prophylaxis of thromboembolism after hip or knee replacement: METHRO I. MElagatran for THRombin inhibition in Orthopaedic surgery.

The novel, oral direct thrombin inhibitor, ximelagatran (formerly H 376/95), represents an advance in antithrombotic therapy through its oral availability. After oral administration, ximelagatran is converted to its active form, melagatran. Melagatran can also be administered subcutaneously (s.c.). The results from the first clinical study with ximelagatran are reported. In this randomized, parallel-group, controlled study, 103 patients scheduled for elective total hip or total knee replacement received s.c. melagatran (1, 2 or 4 mg bid) for 2 days commencing immediately before surgery, followed by oral ximelagatran (6, 12 or 24 mg bid) for 6-9 days. Another 33 patients received dalteparin 5000 IU s.c. once daily, started the evening before surgery, for 8-11 days. At bilateral venography, deep vein thrombosis was found in 20.5% (16/78) of patients who had received s.c. melagatran and oral ximelagatran and in 18.5% (5/27) of patients in the dalteparin group. The study did not evaluate a dose-response for efficacy, and no differences between the three dose levels of melagatran and ximelagatran were shown. No pulmonary embolism was diagnosed during treatment. Total bleeding in the s.c. melagatran plus oral ximelagatran groups showed no dose-response and was similar to that seen in the dalteparin group. The pharmacokinetic properties of melagatran in the surgery patients were consistent with those observed for healthy subjects, and the APTT ratio, which increased non-linearly with plasma melagatran concentration, showed a consistent concentration-effect relationship during the treatment period. Ximelagatran and melagatran were well tolerated. In conclusion, ximelagatran and its active form melagatran appear to be promising agents for the prevention of venous thromboembolism following orthopaedic surgery.