Anti-Xa levels in bariatric surgery patients receiving prophylactic enoxaparin

Limited data exist regarding efficacy and dosing of low-molecular-weight heparins, including enoxaparin, for morbidly obese patients. Prophylactic doses of 30 to 60 mg every 12 h have been described in bariatric surgery patients with appropriate anti-Xa levels reported between 0.18 and 0.6 units/mL.

Fifty-two laparoscopic gastric bypass or banding patients were enrolled. Patients were divided into two groups by the dose of enoxaparin that was given: Group 1--enoxaparin 30 mg every 12 hours--and Group 2--enoxaparin 40 mg every 12 h. Anti-Xa levels were obtained 4 h after the first and third doses. Levels between 0.18-0.44 units/mL were considered appropriate.

There were 19 patients (74% female, mean body mass index [BMI] 48.4 kg/m2) in Group 1 and 33 patients (82% female, mean BMI 48.5 kg/m2) in Group 2. In Group 1, anti-Xa levels were 0.06 and 0.08 units/mL after the first and third doses, respectively. In Group 2, anti-Xa levels were 0.14 and 0.15 units/mL after first and third doses, respectively (p = NS). There was a statistically significant difference in anti-Xa levels between Group 1 first dose and Group 2 first dose (p < 0.05) and between Group 1 third dose and Group 2 third dose (p < 0.05). Percentage of appropriate anti-Xa levels at first dose differed 0% vs. 30.8% (Group 1 vs. Group 2; p = 0.01) and at third dose 9.1% vs. 41.7% (Group 1 vs. Group 2; p = 0.155).

When prophylactic dose enoxaparin of 30 mg every 12 h was changed to 40 mg every 12 h in bariatric surgery patients, anti-Xa levels significantly increased with prophylactic dose enoxaparin in bariatric surgery patients. The percentage of appropriate levels also increased; however, more than half of the patients receiving 40 mg every 12 hours failed to reach therapeutic levels. No levels were supratherapeutic. Dosage of 40 mg every 12 h may not be sufficient for bariatric surgery patients.