Ximelagatran: an oral direct thrombin inhibitor

Non-inferiority Trial Design in Drug Development: A Primer for Cardiovascular Healthcare Professionals

Noninferiority trials, in which a new treatment is compared with a standard active treatment, are becoming increasingly popular in cardiovascular medicine. A noninferiority trial seeks to test whether the effect of a new drug is not unacceptably worse than that of an active comparator by more than a predefined noninferiority margin. Noninferiority trials are typically used when a new drug is anticipated to have an efficacy profile similar to its comparator and offers advantages over the existing drug (better toxicity profile, less expensive, less invasive, simpler regimen, shorter treatment duration, different resistance profile). Given the high number of noninferiority trials, it is vital that clinicians fully understand the clinical impacts of the results. Nonetheless, assessing noninferiority in a trial is complex, in both the design and the analysis phases. The crucial issue in the design of a noninferiority trial is the definition of the noninferiority margin, accounting for both statistical (summarizing the historical evidence of the active comparator from randomized controlled trials) and clinical (choosing the fraction of the effect of the old drug that should be "preserved" by the new drug) considerations. We review the role of noninferiority trials in the development of new cardiovascular treatments and discuss a variety of key issues involved in the design and conduction of noninferiority trials, using some examples from real clinical trials in cardiovascular medicine.

Hepatotoxicity of New Oral Anticoagulants (NOACs)

Case reports and analyses of clinical studies and of pharmacovigilance data suggest that new oral anticoagulants (NOACs) are associated with a small risk for hepatotoxicity. The objective of this publication is to summarize the current data about this subject, with a special emphasis on pharmacovigilance data in the World Health Organization (WHO) Global Individual Case Safety Reports (ICSR) database and on potential mechanisms of hepatotoxicity. For that, all available case reports as well as published analyses of clinical studies were obtained with a detailed search in PubMed. In addition, pharmacovigilance data from VigiBase(®), the WHO Global ICRS database, were extracted and analyzed. The data show that liver injury associated with NOACs was reported in clinical studies and in pharmacovigilance databases. Several case reports described potentially life-threatening hepatotoxicity in patients treated with rivaroxaban or dabigatran. For rivaroxaban, most affected patients were symptomatic and liver injury was most often hepatocellular or mixed. The frequency was between 0.1 and 1 % in clinical studies and was by trend lower than for comparators (mostly enoxaparin or warfarin). Comparing the pharmacovigilance reports for the individual NOACs, more hepatic adverse events were reported for rivaroxaban than for dabigatran or apixaban. With the exception of edoxaban, for which only few reports are available, patients with acute liver failure have been reported for every NOAC, but most patients had concomitant drugs or diseases. So far, there are no clear mechanisms explaining the hepatotoxicity of these drugs. We conclude that hepatotoxicity appears to be associated with all NOACs currently on the market. Hepatotoxicity associated with NOACs is idiosyncratic; it appears at therapeutic doses, is rare and the mechanism is not related to the pharmacological action of these drugs. Prescribers should inform patients about possible symptoms of hepatotoxicity and stop these drugs in patients presenting with severe liver injury.

Ximelagatran for stroke prevention in atrial fibrillation

Atrial fibrillation is the most common sustained cardiac arrhythmia and the most frequently encountered cause of embolic stroke. Vitamin K antagonists (such as warfarin) have represented the cornerstone of anticoagulation practice for the last 60 years. Although highly effective in preventing thromboembolic events among patients with atrial fibrillation, warfarin therapy is limited by a multitude of potential problems. Hence, warfarin is significantly underused in clinical practice, with only half of warfarin-treated patients actually achieving therapeutic anticoagulation in routine clinical practice. Consequently, there is an overwhelming need for an alternative oral anticoagulant for patients with atrial fibrillation that is safer, more practical and effective. Ximelagatran (Exanta, AstraZeneca) is a novel oral direct thrombin inhibitor that is rapidly converted to the active compound melagatran after oral absorption. It has a low potential for drug interactions, anticoagulation monitoring is not required, and it is administered at a fixed twice-daily dose. The Stroke Prevention using the ORal Thrombin Inhibitor in patients with nonvalvular atrial Fibrillation (SPORTIF) III and V trials have together demonstrated the noninferiority of ximelagatran relative to warfarin for the prevention of stroke and embolic events in atrial fibrillation. Unfortunately, initial optimism has been tempered by serious concerns over its safety data in view of its propensity to cause elevation in liver enzymes.

Tissue factor, blood coagulation, and beyond: an overview

Emerging evidence shows a broad spectrum of biological functions of tissue factor (TF). TF classical role in initiating the extrinsic blood coagulation and its direct thrombotic action in close relation to cardiovascular risks have long been established. TF overexpression/hypercoagulability often observed in many clinical conditions certainly expands its role in proinflammation, diabetes, obesity, cardiovascular diseases, angiogenesis, tumor metastasis, wound repairs, embryonic development, cell adhesion/migration, innate immunity, infection, pregnancy loss, and many others. This paper broadly covers seminal observations to discuss TF pathogenic roles in relation to diverse disease development or manifestation. Biochemically, extracellular TF signaling interfaced through protease-activated receptors (PARs) elicits cellular activation and inflammatory responses. TF diverse biological roles are associated with either coagulation-dependent or noncoagulation-mediated actions. Apparently, TF hypercoagulability refuels a coagulation-inflammation-thrombosis circuit in “autocrine” or “paracrine” fashions, which triggers a wide spectrum of pathophysiology. Accordingly, TF suppression, anticoagulation, PAR blockade, or general anti-inflammation offers an array of therapeutical benefits for easing diverse pathological conditions.

Lessons from ximelagatran: issues for future studies evaluating new oral direct thrombin inhibitors for venous thromboembolism prophylaxis in orthopedic surgery

Venous thromboembolism is a frequent complication of total hip and knee replacement requiring prophylaxis with anticoagulants. A direct thrombin inhibitor-ximelagatran-did not show advantages over other anticoagulants and it was withdrawn from the market; however, new drugs are being developed. We conducted a systematic review and meta-analysis to identify conditions under which ximelagatran might potentially be superior to current standards. Medline, EMBASE, the Cochrane Library, and grey literature were screened for randomized trials comparing ximelagatran with warfarin or low-molecular-weight heparin for thromboprophylaxis in total hip or knee replacement. Two reviewers independently assessed and extracted data. A meta-analysis with especial attention to statistical heterogeneity was conducted. This study suggested that the risk-benefit profile of ximelagatran-and probably other similar agents-depends on the type of surgery, the initial timing of administration, and probably the dose. These issues should be explicitly explored in future trials evaluating new direct thrombin inhibitors.

Ximelagatran: An orally active direct thrombin inhibitor

PURPOSE

The chemistry, pharmacology, pharmacokinetics, clinical efficacy, dosage and administration, contraindications, and adverse effects of ximelagatran are reviewed.

SUMMARY

Ximelagatran is the first orally active direct thrombin inhibitor to be tested in Phase III clinical trials. After oral administration, ximelagatran is rapidly converted to its active metabolite, melagatran. Melagatran (after oral ximelagatran administration) predictably inhibits thrombin function without need for routine anticoagulation monitoring. Melagatran effectively inhibits both free and clot-bound thrombin-a potential pharmacodynamic advantage over heparin products. Melagatran has a half-life of 2.4-4.6 hours, necessitating twice-daily administration. Melagatran is primarily eliminated by the kidneys and has not been studied clinically in patients with severe renal failure. Ximelagatran has undergone 10 Phase III trials (6 for prophylaxis of venous thromboembolism [VTE] due to orthopedic surgery, 1 for initial treatment of VTE, 1 for long-term prevention of VTE recurrence, and 2 for stroke prophylaxis due to atrial fibrillation). Results were generally positive. AstraZeneca applied in December 2003 for marketing approval of ximelagatran for prevention of VTE after total knee replacement surgery, long-term prevention of VTE recurrence after standard therapy, and stroke prevention due to atrial fibrillation. FDA denied approval of ximelagatran for all indications, mainly because of increased rates of coronary artery disease events in ximelagatran recipients in some studies and the possibility of hepatic failure when the medication is used for long-term therapy.

CONCLUSION

Ximelagatran has shown promise as a possible alternative to warfarin and other anticoagulants but will require further study to ensure its safety.

Direct thrombin inhibitor use during percutaneous coronary intervention

Direct thrombin inhibitors (DTI) are emerging as alternative anticoagulants to unfractionated heparin and indirect thrombin inhibitors in patients undergoing percutaneous coronary intervention (PCI). We review the pharmacological properties of these newer antithrombotic agents and evaluate the clinical data demonstrating their use in patients undergoing PCI.