Pharmacodynamic Differentiation of Generic Low Molecular Weight Heparins.

Generic LMWHs are available in several countries and several products are currently under review by the FDA. Because there are no regulatory guidelines for defining equivalence of complex biologic drugs, studies were performed to determine whether anti-FXa potency and mean molecular weight are sufficient properties to characterize a generic LMWH as equivalent to the innovator product. Previous in vitro studies have shown differences between generic and name-brand versions of LMWHs in terms of oligosaccharide composition, anticoagulant/anti-protease activity and protamine neutralization profiles. In vivo studies are reported here. The antithrombotic activity of Lovenox (enoxaparin sodium, Sanofi-Aventis, France) and several generic versions (Clenox, Pharmayect, Colombia; Cutenox, Gland Pharma, India; Dilutol, Lazar, Argentina; Dripanina, Ariston, Brazil) was characterized using established animal models of thrombosis [rabbit stasis thrombosis model (RSTM), rat jugular vein clamping model, rat laser-induced thrombosis model] and hemorrhage [rabbit ear bleeding model (REBM)]. Pharmacodynamic studies in non-human primates assessed the effect of LMWH on tissue factor pathway inhibitor (TFPI), nitric oxide (NO), thrombin activatable fibrinolytic inhibitor (TAFI) and tissue factor-induced platelet P-selectin expression. Following IV administration, the ED50 values in the RSTM for Clenox (87±8 μg/kg), Cutenox (91±6 μg/kg) and Dripanina (62±6 μg/kg) were significantly different than that of enoxaparin (72±6 μg/kg). Differing numbers of jugular vein clampings and laser shots were required to induce occlusive thrombi in rats treated with 1 mg/kg Lovenox or the various generic LMWHs. In the laser model, the rank order for number of laser shots was Dilutol = Dripanina < Cutenox < Lovenox < Clenox (range: 4.9 - 7.8 vs. 3.8 with saline). In the clamping model, the rank order for number of clampings was Clenox < Cutenox < Dilutol < Lovenox < Dripanina (range: 4.1 - 6.2 vs. 2.7 with saline). Analysis of blood samples collected when occlusive thrombus formation occurred demonstrated different circulating anti-Xa activity levels of each LMWH, indicating that the antithrombotic effect was not correlated with a similar activity level for all LMWHs (range: 0.9 ± 0.3 to 2.1 ± 0.7 anti-Xa U/ml). Relative to Lovenox (4.1±0.6 RBC×10^9/L), the generic LMWHs produced a significantly higher [Clenox (5.6±1.1 RBC×10^9/L), Dripanina (5.2±0.9 RBC×10^9/L)] or lower [Cutenox (3.0±0.5 RBC×10^9/L), Dilutol (2.9±0.8 RBC×10^9/L)] hemorrhagic effect in the REBM. TFPI levels increased 143% relative to baseline in primates treated with Lovenox, but ranged from 95 to 153% with the generic LMWHs. NO levels increased 11 to 53% following administration of generic LMWHs compared to 56% for Lovenox. Product-dependent differences were observed in the time course of effect on the inhibition of the functionality of TAFIa and the inhibition of tissue factor-induced platelet P-selectin expression. The observed antithrombotic and pharmacodynamic differences among the currently available generic versions of enoxaparin suggest that chemical and biologic differences between generic LMWHs observed in vitro can impact the safety/efficacy of the agent as assessed using animal models. Guidelines for the acceptance of generic LMWHs should include multiple parameters, extending beyond conventional anti-Xa potency and molecular weight distribution. In vivo equivalence studies may be required to validate the biosimilarity of generic and branded LMWHs.]