Summary
Following major orthopaedic surgery, guidelines usually recommend continued thromboprophylaxis
after hospitalisation. The availability of an effective oral anticoagulant with an
acceptable safety profile that does not require routine clinical monitoring may lead
clinicians to switch patients from subcutaneous to an oral therapy either during hospitalisation
or at discharge. The purpose of this study was to assess the effect of enoxaparin
on the pharmacokinetics, pharmacodynamics and safety of apixaban, an oral, direct
inhibitor of coagulation factor Xa. In this four-period, crossover study, 20 healthy
subjects were randomised to receive single doses of apixaban 5 mg orally; enoxaparin
40 mg subcutaneously; apixaban 5 mg and enoxaparin 40 mg concomitantly; and apixaban
5 mg followed 6 hours (h) after by enoxaparin 40 mg. Pharmacokinetics of apixaban
were not affected by enoxaparin. Average peak pharmacodynamic effect, measured by
anti-Xa activity, was 1.36 U/ml after administration of apixaban and was 0.42 U/ml
after enoxaparin. Following co-administration of apixaban and enoxaparin, peak anti-Xa
activity was 42% higher than for apixaban alone. Following administration of enoxaparin
6 h after apixaban, peak anti-Xa activity was 15% higher than for apixaban alone.
In conclusion, enoxaparin had no effect on the pharmacokinetics of apixaban. The increase
in anti-Xa activity after co-administration was modest and appeared to be additive.
Peak anti-Xa activity increases are mitigated by separating administration of subcutaneous
anticoagulation and apixaban when switching between therapies; the potential for pharmacodynamic
interaction may be further mitigated by transitioning at the next scheduled dose (12
h).
Keywords
Apixaban - factor Xa inhibitor - drug switching - pharmacokinetics/pharmacodynamics
- thromboprophylaxis