Rapid Point Coagulation ENOX Test in Patients With Altered Pharmacokinetics of Enoxaparin

Abstract

Background: As the role of enoxaparin expands in the therapeutic armamentarium, so does the role of diagnostic tools, especially the ones that have an edge over the traditional laboratory tests by virtue of being inexpensive, rapid, and accurate. The Rapid Point Coagulation enoxaparin test (ENOX), one such point-of-care test, is designed to determine the anticoagulation effect of enoxaparin. It is emerging as a useful tool, not only in patients undergoing percutaneous coronary interventions, but also in patients whose response to enoxaparin is difficult to predict. We chose to conduct a study to evaluate the usefulness of this bedside test in patients with altered pharmacokinetics of enoxaparin. Methods: This is a correlation study that enrolled 35 patients between April 2003 and November 2003 with renal insufficiency (creatinine clearance <60 mL/min, n = 25), obesity (weight >100 kg, n = 7), and malnourishment (weight <40 kg, n = 3). Whole blood samples were collected from each of the 35 patients, 4 to 8 hours after administration of subcutaneous dose of enoxaparin, in various clinical settings (pulmonary embolism, acute coronary syndrome, atrial fibrillation and deep venous thrombosis). ENOX time and anti-Xa levels were measured simultaneously. Results: A scatter diagram was plotted with ENOX time on the y-axis and anti-Xa levels on the x-axis. The Pearson's correlation coefficient was calculated to be 0.87. A strong degree of agreement between ENOX time and anti-Xa levels was therefore established. Using the critical value table for Pearson's correlation coefficient, a P value of <0.05 was obtained. Anti-Xa level of 0.5–1.8 IU/mL correlated with ENOX time of 200 to 425 seconds, respectively. Conclusions: Clinicians often have reservations in using enoxaparin in patients in whom the response is unpredictable. Our study, although small, shows a strong correlation between the rapid bedside ENOX test and laboratory-based anti-Xa levels even in patients with altered pharmacokinetics. It therefore underscores the use of the point-of-care ENOX test and justifies, with reasonable confidence, the use of this drug in this subset of patients.