Pharmacoequivalence of Enoxaparin and Contaminated Enoxaparin

Introduction: Earlier this year, heparin was found to be contaminated with a non-heparin sulfated polymer identified as oversulfated chondroitin sulfate (OSCS). The presence of this contaminant was associated with severe adverse reactions such as hypotension and anaphylaxis, leading to death in some patients. Some batches of a widely used low-molecular heparin, enoxaparin, also contained OSCS. However, the amount of this contaminant was much lower (less than 5%) in the low-molecular weight heparin batches compared to unfractionated heparin where the amount of the contaminant was up to 30%. Owing to the sizeable number of syringes in Europe that contained the low level of OSCS and the absence of any serious adverse events, the European Medicines Equivalence Agency (EMEA) allowed the qualified use of the subcutaneous administration of the contaminated enoxaparin to ensure access to this essential medication. Despite this, no studies on the anti-thrombotic and bleeding effects or basic physiologic parameters have been reported. To address the bioequivalence of enoxaparin and its contaminated version, studies were undertaken in established animal models of bleeding and thrombosis.

Materials & Methods: Contaminant-free enoxaparin (CFE) and one of the commercially available contaminated enoxaparin (CCE) batches were compared at an equivalent subcutaneous dosage of 2.5 mg/kg in a jugular vein clamping model of thrombosis (n=6/group). A separate group comprised of saline control animals served as control. Blood pressure and heart rate measurements were made at 90 minutes after drug administration, followed by jugular vein clamping model at 120 minutes after drug administration. After the completion of the jugular vein clamping model, blood samples were collected via cardiac puncture for ex-vivo monitoring of anti-coagulant and anti-protease effects.

Results: No differences in the blood pressure and heart rate were observed between the two groups. The anti-thrombotic effects of both the CCE and CFE were measured by jugular vein clamping model. In comparison to the saline treated group (3.5 ± 0.5 clampings), both the CCE and CFE treated animals required a significantly higher number of clampings to induce thrombosis (4.8 ± 0.7 and 5.0 ± 0.6, respectively; p = 0.001 vs. saline; p=0.658 CFE vs. CCE). The ex-vivo analysis of whole blood aPTT revealed a slight elevation in both of the enoxaparin-treated groups in comparison to saline control. (CFE: 36.8 ± 18.6 sec; CCE: 30.5 ± 10.9 sec vs. saline: 26.7 ± 3.9 sec). The anti-Xa effects in plasma were significantly higher with the CFE (84.4 ± 1.5% inhibition) compared to that observed with the CCE (80.5 ± 2.9 % inhibition; p=0.026) while the anti-IIa levels were comparable in the two groups (37.1 ± 22.0 and 30.6 ± 17.9 % inhibition). Ex-vivo analysis of plasma samples from the control group did not reveal any anti-protease or anti-coagulant activity.

Discussion: These results demonstrate that small amounts of OSCS (less than 5%) in enoxaparin do not impact its anti-thrombotic effects when administered subcutaneously. Since OSCS exhibits only anti-IIa activity and does not have any anti-Xa effects, the observed anti-Xa activity of the CCE was less than that of CFE. Other plasmatic anti-coagulant and anti-protease activities were not altered by the presence of OSCS. Since OSCS is highly charged it is likely that upon subcutaneous administration it is not absorbed. This observation is supported by the fact that the anti-Xa and IIa ratios of the samples collected after jugular vein clamping are approximately equal. Thus, the anti-thrombotic and pharmacodynamic effects of the two versions of enoxaparin are identical. The impact of repeated administration of contaminated enoxaparins and long-term pharmacodynamic and immunogenic effects need to be further explored.