A 60 year old gentleman on subcutaneous enoxaparin 80 mg bd for deep vein thrombosis has the following blood results. The blood sample was taken prior to the dose of enoxaparin
INR 1.3 0.9 TO 1.2
APTT 38 SEC 24 to 39
D dimer <0.2 mg/l <0.2 mg/l
Anti Xa 1.8 IU/ml (therapeutic range 0.6 to 1.0 iu/ml)
List 2 likely causes of a raised Anti-Xa level in this patient?
a) If the patient has underlying renal failure
b) body weight is low / incorrect dose of enoxaparin
Anti-Xa level measurements are discussed in some detail in this article from the Australian Prescriber.
However, to answer this question, one does not need to be overfamiliar wiith the methods of anti-Xa testing. The patient has had too much enoxparin, because the level is high.
The college wants to know why he has been overdosed with clexane.
Furthermore, they have done a trough level, suggesting that they were suspecting overdose (or accumulation) to begin with. Typically, when monitoring therapeutic activity, one takes an anti-Xa level about 3-4 hours after the injection is given, to measure the peak effect.
Why might one have abnormally high Anti-Xa at trough?
Usually, this means the enoxaparin is accumulating. Either the dose was too high, or the clearance mechanisms are inadequate to remove an otherwise sensible dose.
The dose was too high:
The clearance mechanisms are inadequate:
Barras, Michael. "Anti-Xa assays." AN INDEPENDENT REVIEW (2013): 98.
The Sanofi pamphlet for its brand of enoxaparin has a surprisingly detailed breakdown of its elimination pharmacokinetics.
Fareed, Jawed, et al. "Pharmacodynamic and pharmacokinetic properties of enoxaparin." Clinical pharmacokinetics 42.12 (2003): 1043-1057.
Friedrich, E., and A. B. Hameed. "Fluctuations in anti-factor Xa levels with therapeutic enoxaparin anticoagulation in pregnancy." Journal of Perinatology30.4 (2009): 253-257.
Bazinet, Annie, et al. "Dosage of enoxaparin among obese and renal impairment patients." Thrombosis research 116.1 (2005): 41-50.