Elderly medical patients treated with prophylactic dosages of enoxaparin - Influence of renal function on anti-Xa activity level

Background: The safety and optimal use of prophylactic treatment with low-molecular-weight heparins in elderly patients with impaired renal function remain undefined. Methods: The primary aim of this study was to analyse, in 'real life', the influence of renal function, as assessed by creatinine clearance (CLCR), on the level of anti-Xa activity in medical hospitalised elderly patients receiving prophylactic dosages of enoxaparin. Consecutive hospitalised acutely ill medical patients aged >= 75 years receiving daily dosages of enoxaparin 4000IU for up to 10 days were prospectively enrolled in two centres. Peak anti-Xa activity was measured at the beginning and during the course of therapy. Results: One hundred and twenty-five patients (31 men, 94 women), mean age 87.5 +/- 6.3 years, mean bodyweight 56.4 +/- 11.9kg and mean CLCR 39.8 +/- 16.1 mL/min, were enrolled in the study. The mean maximum anti-Xa activity (day I to day 10) [anti-Xa(max1-10)] was 0.64 +/- 0.23 IU/mL (range 0.24-1.50 IU/mL). Weak negative correlations were found between CLCR and anti-Xa(max) and between bodyweight and anti-Xamax. Mean anti-Xamax was slightly but significantly higher in patients with CLCR of 20-30 mL/min compared with patients with CLCR of 31-40,41-50 or 51-80 mL/min (0.72 versus 0.61, 0.61 and 0.60 IU/mL, respectively), and in patients weighing < 50kg compared with patients weighing 50-60kg or > 60kg (0.74 vs 0.64 and 0.52 IU/mL, respectively). Serious bleeding occurred in five patients, but anti-Xa(max) values in these patients were not different to those in patients without bleeding (p = 0.77). Individual anti-Xa(max) at the beginning or during the course of treatment was measured in the subgroup of 58 patients in whom anti-Xa activity was measured at least once during the study. The mean anti-Xa(max) value was slightly but significantly higher during the course of the therapy than at the beginning of the study (0.63 +/- 0.26 IU/mL vs 0.56 +/- 0.23 IU/mL, p = 0.012). Conclusion: Only CLCR < 30 mL/min and bodyweight < 50kg were associated with significantly higher anti-Xamax values. The clinical relevance of these increases remains questionable. No conclusions about the safety of enoxaparin in elderly medical patients can be drawn from these findings.