Weight-adjusted dosing of tinzaparin for thromboprophylaxis in obese medical patients.

BACKGROUND

The optimal dose of tinzaparin for prophylaxis in obese medical patients is not well defined.

OBJECTIVES

To evaluate the anti-Xa activity in obese medical patients on tinzaparin prophylaxis adjusted for actual bodyweight.

METHODS

Patients with a body mass index of ≥30 kg/m treated with 50 IU/kg tinzaparin once daily were prospectively included. Anti-Xa and anti-IIa activity; von Willebrand factor antigen and von Willebrand activity; factor VIII activity; D-dimer, prothrombin fragments; and thrombin generation were measured 4 hours after subcutaneous injection between days 1 and 14 after the initiation of tinzaparin prophylaxis.

RESULTS

We included 121 plasma samples from 66 patients (48.5% women), with a median weight of 125 kg (range, 82-300 kg) and a median body mass index of 41.9 kg/m (range, 30.1-88.6 kg/m). The target anti-Xa activity of 0.2 to 0.4 IU/mL was achieved in 80 plasma samples (66.1%); 39 samples (32.2%) were below and 2 samples (1.7%) above the target range. The median anti-Xa activity was 0.25 IU/mL (IQR, 0.19-0.31 IU/mL), 0.23 IU/mL (IQR, 0.17-0.28 IU/mL), and 0.21 IU/mL (IQR, 0.17-0.25 IU/mL) on days 1 to 3, days 4 to 6, and days 7 to 14, respectively. The anti-Xa activity did not differ among the weight groups ( = .19). Injection into the upper arm compared to the abdomen resulted in a lower endogenous thrombin potential, a lower peak thrombin, and a trend to a higher anti-Xa activity.

CONCLUSION

Dosing of tinzaparin adjusted for actual bodyweight in obese patients achieved anti-Xa activity in the target range for most patients, without accumulation or overdosing. In addition, there is a significant difference in thrombin generation depending on the injection site.