Use Of Fondaparinux For Venous Thromboembolism Prophylaxis In Critically Ill Adult Patients With Moderate Renal Insufficiency
Authors: Patel Anjan J , Zumberg Marc , Cope Jessica , Bushwitz Jennifer , Antigua Abigail D 
Published: October 2019

Introduction
Fondaparinux, a selective activated Factor Xa inhibitor, is a parenteral anticoagulant primarily excreted by the kidneys. Renal insufficiency (RI), commonly encountered in the critically ill, has been shown to portend an increased risk of bleeding than in normal healthy adults. In comparison to the low molecular weight heparin dalteparin, fondaparinux has been shown to be superior for the prevention of post-surgical venous thromboembolism (VTE), however an increased rate of nonfatal bleeding has been observed. Recently, data has emerged supporting empiric dose reductions in patients with moderate RI, defined as a creatinine clearance (CrCl) between 30 and 50 mL/min. Overall, the data supporting appropriate use of fondaparinux in patients with RI is lacking. This retrospective, single center study describes our experience using prophylactic fondaparinux in critically ill patients with moderate RI.

Methods
We report our experience utilizing fondaparinux in a mixed medical and surgical, critically ill adult population with moderate RI. The site examined was UF Health; an 852-bed sized tertiary care hospital in Gainesville, Florida between 2006 and 2012. Moderate RI was defined as a CrCl between 30 and 50 mL/min calculated by the Cockcroft/Gault equation. Only patients treated with fondaparinux for prophylaxis of VTE were included, patients treated for other indications were excluded. Doses, dose frequency and dose adjustments were documented. If patients had anti-Xa level monitoring these values were recorded. Timing of anti-Xa levels drawn with respect to fondaparinux dosing was also noted. The primary end point of the study was the rate of clinically significant bleeding events in patients receiving at least 72 hours of fondaparinux. Clinically significant bleeding was defined as transfusion of at least two units of packed red blood cells within 48 hours of a documented bleeding event or the workup of bleeding with endoscopy or imaging. Bleeding events were screened by ICD-9 codes and validated via chart review, incidence of VTE was also noted.

Results
Sixty-fourpatients met inclusion criteria between October 2006 and November 2012. Two patients (3.1%) experienced clinically significant bleeding events as per our definition, both in the form of gastrointestinal bleeding. Empiric dose reductions occurred in 8 (12.5%) patients, this occurred in the form of every other day administration or dose reduction using fondaparinux 1.25mg daily. Nine (14%) patients were monitored with anti-Xa levels, none of these patients encountered bleeding events. The median anti-Xa level was 0.5 mcg/mL, which is in the target prophylactic range for in our lab. The median time interval after last dose of fondaparinux to anti-Xa level measurement was 4 hours. Seven (10.9%) patients had VTE diagnoses prior to the initiation of prophylactic fondaparinux. No patients suffered a VTE event after treatment with prophylactic fondaparinux in our data set.

Conclusion
We report a cohort of patients with moderate RI receiving fondaparinux for the prevention of VTE. The incidence of clinically significant bleeding was 3.1%. The risk of VTE was low, no patients suffered from a VTE after treatment with fondaparinux in our data set. The rate of bleeding is slightly higher compared to patients with normal renal function. Our experience over this 6 year period supports the notion that RI portends an increased risk of bleeding with the use of fondaparinux. Further prospective studies are needed to determine the safety and efficacy of empiric fondaparinux dose reductions in patients with RI and end stage renal disease. Anti-Xa monitoring may help reduce the risk of bleeding in this patient population by identifying those patients in whom a dose reduction may be beneficial.

Disclosures:
No relevant conflicts of interest to declare.