Use of Thrombin Generation Assay As Tool for the Evaluation of the Antithrombotic Samenesse of Enoxaparine Copies

Background. The protection rights of LMWHs expired or are expiring, so the extent and nature of the studies required to obtain a market authorization for LMWH copies is an issue of debate. The actual situation, which is characterized by the increasing number of enoxaparin copies available worldwide, makes the definition of criteria for the biological similarity between LMWHs copies and the original product a real need.

Aim. The present study, conducted in vitro, offers an analytical approach for the comparison of branded enoxaparin and its copies using a standard pharmacological assay (the measurement of the specific anti-Xa activity) and the calibrated automated thrombogram performed in human platelet rich or platelet poor plasma (PRP and PPP) as well as in an experimental model of hypercoagulability induced by cancer cells. The study aims to provide an integrated rational for the determination of the criteria for the similarity and sameness of branded and copies of enoxaparin.

Methods. The studied copies of enoxaparin were Cutenox®, Dilutol®, Enoxa®, Fibrinox®, Loparin®, Lupenox®, Novex®, Noxprin®, Versa®. Samples of PPP and PRP from 15 volunteers were spiked with 2-20 µg/ml of branded (Lovenox®) or copies of enoxaparin. The specific anti-Xa activity in PPP was measured with the Rotachrom® assay. Thrombin generation in PPP and PRP in the presence of tissue factor or pancreatic cancer cells BXPC3 was assessed with the Calibrated Automated Thrombogram. Among thrombogram parametersn the Mean Rate Index (MRI) of TG propagation phase of thrombin generation was analysed. The concentrations inhibiting 50% (IC50) the MRI were calculated.

Results . The specific inhibitory potency of enoxaparin copies against factor Xa ranged from 0.072 to 0.088 anti-Xa IU/μg, being lower as compared to that of the branded enoxaparin (0.095 anti-Xa IU/μg). the branded enoxaparin induced a concentration dependent inhibition of thrombin generation. The IC50 values revealed significant differences among the studied copies of enoxaparin and between each one of them and the branded enoxaparin. The potency of each copy of enoxaparin to inhibit thrombin generation as compared to the branded product varied in the three experimental systems. the presence of platelets or pancreatic cancer cells in human plasma induces significant modifications of the inhibitory potency of enoxaparin copies on thrombin generation, which distinguish them not only from the branded enoxaparin but also among them.

Conclusion. the copies of enoxaparin which respond to the criteria of sameness to the branded enoxaparin according to the pharmacological criteria endorsed by health authorities demonstrate a significant variability regarding their inhibitory potency on thrombin generation. The presence of platelets and cancer cells significantly influence the variability of the antithrombotic efficiency of the enoxaparin copies as compared to the branded product. The findings of the present study underline the need for the elaboration of functional criteria which evaluate the global antithrombotic capacity of enoxaparin copies in order to evaluate their potential sameness with the branded drug.