Background: Enoxaparin dosage for obese patients and patients with renal impairment remains controversial.
Objective: To compare anti-factor Xa activity (anti-Xa) among obese and renal impairment patients to patients with healthy weight and adequate renal function.
Design: Open, prospective, nonrandomized clinical trial.
Setting: A major community teaching hospital.
Patients: A total of 233 patients with prescription of enoxaparin.
Interventions: Enoxaparin 1.5 mg/kg once daily or 1 mg/kg twice daily except those on dialysis, who received 75% of the dose.
Measurements: Anti-Xa was measured 4 h post-injection on day 2 or 3.
Results: Mean (95% confidence interval (95% CI)) anti-Xa was equal to 1.14 IU/mL (1.07-1.21) and 1.14 IU/mL (1.08-1.20) among patients who received one (n=92) and two injections (n=122) per day, respectively. Anti-Xa increases with body mass index (BMI) (0.01 IU/mL for each kg/m2; 95% CI: 0.002-0.017), but the increase is insufficient to reach supratherapeutic anti-Xa. Anti-Xa decreases with higher creatinine clearance (CrCl) (-0.003 IU/mL for each mL/min; 95% CI: -0.006 to -0.001). On the twice-daily regimen, this is sufficient to reach supratherapeutic anti-Xa. The odd ratio (OR) (95% CI) of having a nontherapeutic anti-Xa is equal to 2.28 (1.25-4.16) when enoxaparin is administered twice daily and to 3.03 (1.16-7.86) among severe renal impairment patients (< or =30 mL/min).
Conclusions: Based on Anti-Xa, no dosage adjustments are required in obese patients. In renally impaired patients, adjustments may be necessary when enoxaparin is administered twice daily.