Comparison of the Pharmacokinetic and Pharmacodynamic Behavior of Branded and Generic Enoxaparin in Non-Human Primates

Low molecular weight heparins (LMWHs) have been shown to be safe and effective in the prevention and treatment of venous thrombosis and in the treatment of patients with pulmonary embolism or acute coronary syndrome. Commercially available LMWHs are distinct agents in terms of their molecular weight profile and in vitro potency. Molecular weight influences the pharmacokinetics (PK) and pharmacodynamics (PD) of heparin oligosaccharides. Although there continues to be interest in developing biosimilar versions of LMWHs, defining biosimilarity for LMWHs is challenging because chemical means of measuring plasma heparin levels do not exist, potency measures typically only measure AT-dependent activities, bioequivalence in terms of one activity does not ensure identical pharmacokinetic behavior in terms of other biological activities and identification and quantification of the various oligosaccharide components in a LMWH preparation is difficult. In vitro studies have shown that biosimilar LMWHs can differ considerably from the branded product as well as from each other. In the current study, the PD behavior of branded and biosimilar enoxaparin was compared in a cross-over study following a single subcutaneous dose to non-human primates.

Lovenox (lot #514956, sanofi-aventis, Paris, France) and Fibrinox (lot#0002, Sandoz S.A., Buenos Aires, Argentina) were obtained in pre-filled syringes at a concentration of 100 mg/ml. Upon anesthesia, the non-human primates (Macaca mulatta) were weighed and a baseline blood sample was collected. A site on the abdomen was shaved and cleansed prior to the subcutaneous administration of LMWH. Blood samples were collected at 1, 4, 6 and 28 hours post-administration and were centrifuged to make platelet poor plasma which was stored in aliquots at −70°C until analysis. Primates were randomly dosed with one of the two test agents. After a minimum of one week wash-out, the same primates were dosed with the other test agent. Plasma samples were evaluated using clot-based and amidolytic assays. LMWH concentrations in the blood samples were determined by extrapolation from in vitro concentration-response curves and used to calculate values for PK parameters. p-values < 0.05 determined by two-way repeated measures analysis of variance were considered to be statistically significant.

LMWH levels determined by circulating anti-Xa activity following Fibrinox and Lovenox administration were not observed to be significantly different. Circulating anti-IIa levels, however, were significantly higher in Lovenox-treated animals at 1, 4 and 6 hours post-administration. Using the Heptest assay, higher circulating drug levels were measured in Fibrinox-treated animals at 4 and 6 hours. A high degree of variability was observed in the absorption and elimination of the LMWHs. Statistically significant differences in pharmacokinetic behavior was not observed when circulating drug concentrations were determined using anti-Xa activity or Heptest prolongation. Using drug concentrations determined from anti-IIa activity, the AUC following Lovenox treatment was significantly larger than following Fibrinox treatment. Plotting mean drug levels based on anti-IIa activity versus mean drug levels based on anti-Xa activity at the various sample times indicated a hysteretic relationship which was distinct for Fibrinox and Lovenox-treated primates. Clear differentiation of the two LMWHs was also observed when drug levels measured by anti-IIa activity were plotted against those determined using the prolongation of the Heptest.

Potency of LMWHs can be expressed in terms of a number of AT-dependent and AT-independent activities, which may not be proportional. The PK/PD behavior of LMWHs is different when drug levels are determined using distinct biologic activities. The measured concentration of a drug and its corresponding effect can be asynchronous, that is, peak drug levels may not occur at the same time as peak effect levels. In this study, plotting drug concentrations determined by one functional parameter against those derived from a different parameter provided clear visual evidence that the two LMWHs tested exhibit distinct pharmacodynamic behavior. In vivo behavior is an important consideration for defining pharmacoequivalence of complex biologic drugs.

No relevant conflicts of interest to declare.