Evaluation of impact of clinical variables on enoxaparin dosing and anti-Xa factor concentration

Enoxaparin, a low molecular weight heparin, is widely used for venous thromboembolism treatment and prevention. While routine anti-factor Xa (anti-Xa) monitoring is not generally required, it may be valuable in high-risk populations such as patients with obesity or renal impairment.

To evaluate the impact of clinical variables on therapeutic enoxaparin dosing and assess the effectiveness of anti-Xa monitoring in real-world clinical practice.

A retrospective, single-centre, descriptive study was conducted in adults admitted to hospital and receiving therapeutic enoxaparin with correctly timed peak anti-Xa measurements (4 hours after dose) between December 2021 and January 2023. Demographic, clinical and dosing data were extracted from medical records. Predictors of peak anti-Xa concentration were identified using multiple linear regression. Dose-concentration correlations were examined overall and by obesity status.

A total of 146 patients were included (mean age 67±12.3 years; 56.2% male; mean body mass index 29.6±7.5 kg/m²; 30.1% with obesity). Enoxaparin dose (p<0.001) and obesity (p=0.007) were independent predictors of peak anti-Xa concentration; renal impairment and critical illness were not. The correlation between dose and concentration was strong in patients without obesity (r=0.56) but weak in those with obesity (r=0.16). Only 46.6% achieved therapeutic concentrations; 40.4% were subtherapeutic and 12.9% supratherapeutic. Among patients with out-of-range values, dose adjustments were made in 67.9%, but follow-up anti-Xa measurement occurred in only 45.3%; 79.2% of these achieved target concentrations.

Obesity significantly influences enoxaparin pharmacokinetics, reducing predictability of anti-Xa concentrations with actual body weight dosing. Targeted anti-Xa monitoring in high-risk groups, particularly patients with obesity, and structured dose-adjustment protocols may improve therapeutic achievement and safety.