Anti-Xa Levels 4 h After Subcutaneous Administration of 5,700 IU Nadroparin Strongly Correlate with Lean Body Weight in Morbidly Obese Patients

Background Morbidly obese patients (BMI > 40 kg/m 2 ) are at increased risk for venous thromboembolism, especially after surgery. Despite limited evidence, morbidly obese patients are often administered a double dose of nadroparin for thromboprophylaxis compared to non-obese patients. The aim of this study was to evaluate the influence of different body size descriptors on anti-Xa levels after a double dose of nadroparin (5,700 IU) in morbidly obese patients. Methods In 27 morbidly obese patients with a mean total body weight of 148 kg (range 107–260 kg), anti-Xa levels were determined peri-operatively until 24 h after administration of a subcutaneous dose of 5,700 IU of nadroparin. Results Anti-Xa level 4 h after administration (A 4h , mean 0.22 ± 0.07 IU/ml) negatively correlated strongly with lean body weight ( r = −0.66 ( p < 0.001)) and moderately with total body weight ( r = −0.56 ( p = 0.003)) and did not correlate with body mass index ( r = −0.26 ( p = 0.187)). The area under the anti-Xa level-time curve from 0 to 24 h (AUA 0–24h , mean 2.80 ± 0.97 h IU/ml) correlated with lean body weight ( r = −0.63 ( p = 0.007)), but did not correlate with total body weight ( r = −0.44 ( p = 0.075)) or body mass index ( r = −0.10 ( p = 0.709)). Conclucions Following a subcutaneous dose of nadroparin 5,700 IU, A 4h and AUA 0–24h were found to negatively correlate strongly with lean body weight. From these results, individualized dosing of nadroparin based on lean body weight should be considered in morbidly obese patients.