The need for monitoring should be determined on a case-by-case basis.

In general, because response to Clexane® at usual doses is consistent from patient to patient, the anticoagulant response to enoxaparin does not need to be monitored. LMWHs have a predictable dose-response relationship and Clexane® has a half-life that permits once- or twice-daily dosing. This facilitates simple fixed or weight-based dosing, enabling outpatient treatment in appropriate cases without the need for routine monitoring. This is reflected in the Summary of Product Characteristics [42].

Changes in blood clotting parameters such as thrombin time or activated partial thromboplastin time (aPTT) do not display a linear correlation with antithrombotic activity. Therefore these parameters are not suitable for monitoring purposes. However, anticoagulant activity of enoxaparin can be monitored by measuring factor Xa inhibition (anti-factor Xa activity). The plasma anti-Xa assay is a laboratory test that indirectly measures the activity of heparins [46]. It is predominantly used for monitoring patients treated with low molecular weight heparins, particularly when dosing at the extremes of weight and in patients who are pregnant, critically ill or have renal impairment [46].

This monitoring is controversial as there is a poorly defined therapeutic range in different clinical settings and with different dosing regimens. Consequently, the timing of blood tests and their interpretation is problematic, often resulting in empirical dosing strategies [46].

Platelet count monitoring

As there is a risk of antibody-mediated heparin-induced thrombocytopenia occurring with low molecular weight heparins, regular platelet count monitoring should be considered prior to and during therapy with these agents. Thrombocytopenia, should it occur, usually appears between the 5th and the 21st day following the initiation of therapy and may be complicated by thrombisis. Therefore, it is recommended that the platelet counts be measured before the initiation of therapy with Clexane® and then regularly thereafter during the treatment. In practice, if a confirmed significant decrease of the platelet count is observed (30 to 50% of the initial value), enoxaparin sodium treatment must be immediately discontinued and the patient switched to another therapy [42].