Generic Forms of Low-Molecular-Weight Heparins: Some Practical Considerations

Product Individuality of Commercially Available Low-Molecular-Weight Heparins and Their Generic Versions: Therapeutic Implications

The currently available brand-name low-molecular-weight heparins (LMWHs) in the United States include dalteparin (Pfizer), enoxaparin (Aventis), and tinzaparin (Pharmion). Other products available, in Europe, include certoparin (Novartis), reviparin (Abbott), nadroparin (GlaxoSmithkline), and parnaparin (Alpha-Wasserman). Each of these LMWHs has a characteristic molecular weight profile and biological activity in terms of an anti-FXa and anti-FIIa potency. The mean molecular weight of these drugs ranges from 4.0 kDa to 7.0 kDa and the anti-FXa:anti-FIIa ratio ranges from 1.5 to 3.5. These agents may also be characterized by the presence of specific chemical end groups such as 2-O-sulfo-4-enepyranosuronic acid at the nonreducing terminus (enoxaparin) or 2,5-anhydro-D-mannose at the reducing terminus (dalteparin). Further, the component oligosaccharide chains exhibit product-specific distribution profiles. It is now widely accepted that individual LMWHs are chemically unique agents and cannot be interchanged therapeutically. Each commercial LMWH has been individually developed for specific clinical indications, which are dose and product dependent. Recently, several generic LMWHs have become available in India (Cutenox and Markaparin) and South America (dilutol, clenox, dripanina), and three companies have filed for regulatory approval of a generic version of enoxaparin in the United States. As the primary aim of a generic drug is to reduce cost without compromising patient care, a generic drug is required to be chemically and biologically equivalent to the pioneer drug. Because LMWHs represent complex natural mucopolysaccharide drugs that have undergone chemical and enzymatic modifications, physicochemical and biological information in addition to molecular weight and anti-FXa:anti-FIIa ratio should be used to determine generic equivalency to the branded drug. We have utilized a previously reported approach to systematically compare three generic versions of enoxaparin obtained from India and Brazil with the branded enoxaparin (Lovenox) available in the United States. Testing included molecular and structural profiling, evaluation in clot-based and amidolytic anti-FXa and anti-FIIa assays, and heparinase-I digestion profiles. While the molecular profiles (4.8 ± 1.8kD) and anticoagulant potencies as determined by activated partial thromboplastin time (APTT) were comparable for all four agents, the generic products showed variations in the thrombin time (TT) and Heptest assays. Two generic and the branded enoxaparin were readily digested by heparinase-I, losing most of their anticoagulant activity, but one generic product resisted digestion. This may have been due to a unique structural feature in this product. These studies show that, while generic LMWHs may exhibit acceptable molecular weight and anti-FXa profiles, they can exhibit assay-based differences and digestion profiles. Testing in animal models to determine safety, efficacy, and pharmacodynamic parameters may be important to verify equivalence. In order to assure that the generic LMWHs are equivalent to branded LMWHs such that equivalent clinical results are obtained, there is a need to develop clear stepwise guidelines that will establish equivalency in terms of physical, chemical, biochemical, pharmacokinetic, and pharmacodynamic properties for these anticoagulant drugs.

Generic Versus Branded Enoxaparin in the Prevention of Venous Thromboembolism Following Major Abdominal Surgery

Introduction: Several generic low-molecular-weight heparins (LMWHs) have recently become available worldwide, including the United States. Companies have filed for regulatory approval of generic versions in many countries, based only on compound biochemical characteristics or its immunogenicity. Methods: Prospective study to evaluate the comparative effect of 2 enoxaparins (Sanofi-Aventis branded enoxaparin [SAe] vs eurofarma-enoxaparin [Ee], a generic version) as prophylaxis for venous thromboembolism (VTE) following major abdominal surgery. A total of 200 patients were randomized in a 1:1 ratio either to receive 40 mg of SAe or Ee subcutaneously (sc) once daily (od) postoperatively for 7 to 10 days. Compressive ultrasound was performed on day 10 + 4. Results: No statistically significant differences between the 2 groups were detected. In all, 2 SAe patients presented deep vein thrombosis ([DVT] 2.1%), none of the Ee group. No major bleeding events occurred. Conclusions: This exploratory trial suggests that the generic LMWH is probably as safe and as effective as the branded enoxaparin (Lovenox, Brazil) in the prophylaxis of VTE in this population.

Structural and functional characterization of low-molecular-weight heparins: impact on the development of guidelines for generic products

Low-molecular-weight heparins (LMWHs) are poly-pharmacologic drugs used to treat thrombotic and cardiovascular disorders. Recently, several generic versions of branded LMWHs have been introduced. Although generic versions of LMWHs exhibit similar profiles, marked differences in their biological and pharmacologic properties have been demonstrated. Several studies have demonstrated differences in terms of anti-Xa activity and tissue factor pathway inhibitor release. The current data emphasize the need to consider multiple functional parameters when defining bioequivalence of biologic drugs and also underscore the importance of further pharmacologic studies involving animal and human clinical trials. The US Food and Drug Administration (FDA) and the European Medicines Agency (EMEA) are currently developing guidelines for the acceptance of complex biological drugs including LMWHs. The US FDA considers these drugs as follow-on agents whereas the EMEA classifies these drugs as biosimilar agents. Until clear guidelines are developed, generic interchange of LMWHs may not be feasible.

Are all low molecular weight heparins equivalent in the management of venous thromboembolism?

Low molecular weight heparins are replacing unfractionated heparin in a number of clinical indications because of their improved subcutaneous bioavailability and more predictable antithrombotic response. Clinical trials have demonstrated that low molecular weight heparins are at least as safe and effective as unfractionated heparin for the initial treatment of venous thromboembolism, and unfractionated heparin and warfarin for primary and secondary thromboprophylaxis. The mechanism behind the antithrombotic action of low molecular weight heparins is not fully understood but is likely to involve inhibition of coagulation factors Xa and IIa (thrombin), release of tissue-factor-pathway inhibitor, and inhibition of thrombin activatable fibrinolytic inhibitor. Different low molecular weight heparins have been shown to have various effects on coagulation parameters. Seven low molecular weight heparins are currently marketed worldwide, each demonstrated distinct chemical entities with unique pharmacokinetic and pharmacodynamic profiles. Each low molecular weight heparin is approved for specific indications based on the available efficacy and safety data for that product. The relative efficacy and safety of the low molecular weight heparins are unclear because there have been very few direct comparisons in randomized clinical trials. While recommending low molecular weight heparins for the prevention and treatment of venous thromboembolism, clinical guidelines have not specified individual agents. National and international organizations recognize that low molecular weight heparins are distinct entities and that they should not be used interchangeably in clinical practice. Each low molecular weight heparin should be used at the recommended dose when efficacy and safety data exist for the condition being treated. When these data are not available, the dosing and administration of low molecular weight heparins must be adapted from existing data and recommendations.