Glomerular filtration rate estimated by Cockcroft-Gault formula better predicts anti-Xa levels than modification of the diet in renal disease equation in older patients with prophylactic enoxaparin.

OBJECTIVES: Older people have an increased risk of low molecular weight heparin accumulation leading to an increased bleeding risk. The objective of this study was to assess whether reduced glomerular filtration rate (GFR), estimated by the Cockcroft-Gault or modification of the diet in renal disease (MDRD) equations, indicates drug accumulation by increased anti-Xa levels in older subjects receiving prophylactic enoxaparin treatment.
DESIGN: Cohort study.
SETTING: Acute geriatric units in Nancy Hospital. PARTICIPANTS: Ninety-two consenting consecutive patients, 65 and older, confined to bed for an acute medical condition requiring enoxaparin for prevention of venous thromboembolism, and hospitalized for at least six days were enrolled. MEASUREMENTS: Serum creatinine and peak plasma anti-Xa levels 3 to 4 hours after the daily injection of enoxaparin were measured at days 3, 6, 9 and 12 (first dose of enoxaparin at day one). Analyses of variance for repeated measures were used to evaluate significant predictors of peak anti-Xa activity in univariate and multivariate analyses.
RESULTS: A significant correlation was observed between anti-Xa activity and GFR estimated with the Cockcroft formula r=0.43. Following univariate analysis, the three factors associated with higher anti-Xa levels were a lower Cockcroft-Gault GFR (p=0.0002), female gender (p=0.0003) and a lower bodyweight (p<.0001). No significant association between anti-Xa levels and MDRD GFR (p=0.33) was observed. Following multivariate analysis, female gender (p=0.02), bodyweight (p=0.04) and Cockcroft GFR (p=0.05) remained independent determinants of anti-Xa levels.
CONCLUSION: In hospitalized patients older than 65 years old, the Cockcroft-Gault equation, in contrast to the MDRD equation, is able to predict the risk of higher anti-Xa levels.