Plasma accumulation of fondaparinux 2.5 mg in patients after total hip arthroplasty

Fondaparinux (FPX), a selective inhibitor of factor Xa, is widely used for the prophylaxis of venous thromboembolism (VTE) after total joint arthroplasty. However, the association between plasma FPX concentration and adverse events and the occurrence of VTE has not been clarified thus far. We aimed to prospectively evaluate these associations by measuring anti-Xa activity of FPX in patients undergoing total hip arthroplasty (THA) and investigate whether factors such as age, body weight, and renal function influence the anti-Xa levels. We enrolled 85 patients who underwent primary THA. All patients received subcutaneous FPX (2.5 mg/day for 14 days) after surgery. Anti-Xa activity was measured on postoperative days 1, 3, 7, and 14. To assess VTE, multidetector row computed tomography was performed in all patients at 1 week after surgery. The median levels of anti-Xa activity increased as follows (medians with 95 % confidence interval): 0.00 (0.00–0.01) mg/L, 0.13 (0.11–0.14) mg/L, 0.19 (0.17–0.20) mg/L, and 0.24 (0.22–0.25) mg/L on postoperative days 1, 3, 7, and 14, respectively. The plasma accumulation of FPX was more likely in patients with renal impairment than in those with normal renal function. In contrast, a poor correlation was observed between the plasma levels of anti-Xa activity and age or body weight. No differences were observed in the anti-Xa activity in patients with and without postoperative VTE or bleeding. Substantial increase in the levels of anti-Xa activity was observed, especially in patients with renal impairment, after subcutaneous administration of FPX 2.5 mg after THA.