Fondaparinux

• DVT Prevention
• Pulmonary Embolism Treatment
• Post-Surgical Thromboprophylaxis
• Anticoagulation in HIT

Fondaparinux is a synthetic pentasaccharide anticoagulant that selectively inhibits factor Xa, used for the prevention and treatment of venous thromboembolism. This medication provides predictable anticoagulation with once-daily subcutaneous dosing and does not cause heparin-induced thrombocytopenia.

Mechanism of Action

Fondaparinux is a synthetic pentasaccharide that represents the minimal antithrombin III (AT) binding sequence of heparin. It binds selectively and with high affinity to AT, inducing a conformational change that enhances AT's inhibition of factor Xa by approximately 300-fold. Unlike heparin and low molecular weight heparins, fondaparinux is too short to bridge AT to thrombin, so it has no direct anti-thrombin (anti-IIa) activity. This selective anti-Xa activity results in dose-dependent inhibition of thrombin generation without directly affecting thrombin activity or platelet function. The predictable pharmacokinetics allow for fixed-dose or weight-based dosing without routine monitoring.

Available Formulations

Fondaparinux sodium is available as a solution for subcutaneous injection in single-dose prefilled syringes containing 2.5 mg/0.5 mL, 5 mg/0.4 mL, 7.5 mg/0.6 mL, and 10 mg/0.8 mL. The medication should be stored at room temperature. Each syringe is intended for single use only.

Medical Uses

Fondaparinux is FDA-approved for prophylaxis of DVT in patients undergoing hip fracture surgery, hip replacement surgery, knee replacement surgery, or abdominal surgery at risk for thromboembolic complications; treatment of acute deep vein thrombosis when administered with warfarin; treatment of acute pulmonary embolism when administered with warfarin (in appropriate patients); and treatment of acute superficial vein thrombosis of the legs. It is an alternative to heparin in patients with a history of heparin-induced thrombocytopenia.

Dosing Guidelines

For prophylaxis, 2.5 mg subcutaneously once daily starting 6-8 hours post-surgery, continuing for 5-9 days (up to 32 days for hip fracture surgery). For DVT/PE treatment, weight-based dosing: less than 50 kg: 5 mg; 50-100 kg: 7.5 mg; greater than 100 kg: 10 mg subcutaneously once daily, continued until adequate oral anticoagulation is achieved (minimum 5 days and INR 2-3 for warfarin). The first prophylactic dose should be given no earlier than 6 hours after surgery to reduce bleeding risk.

Important Safety Information

Fondaparinux is contraindicated in patients with severe renal impairment (CrCl less than 30 mL/min) for treatment indications and in patients with body weight less than 50 kg for prophylaxis (increased bleeding risk). It carries a boxed warning for epidural or spinal hematomas in patients receiving neuraxial anesthesia or undergoing spinal puncture. Major bleeding is the primary adverse effect. There is no specific reversal agent; protamine is ineffective. Unlike heparin, fondaparinux does not cause HIT and is an option for patients with HIT history.

Drug Interactions

Drugs that affect hemostasis (anticoagulants, antiplatelet agents, NSAIDs, thrombolytics) increase bleeding risk. Fondaparinux should be discontinued before initiating treatment with other anticoagulants. No significant pharmacokinetic interactions have been identified, as fondaparinux is eliminated primarily renally without metabolism. Routine monitoring with anti-Xa assays is not required but may be helpful in certain populations (renal impairment, extremes of body weight).

Special Populations

Fondaparinux is pregnancy category B; animal studies showed no fetal harm, but human data are limited. Use during pregnancy only if clearly needed. It is unknown whether fondaparinux is excreted in human breast milk; use caution during breastfeeding. Safety and efficacy have not been established in pediatric patients. Elderly patients may have increased bleeding risk due to age-related renal function decline. The medication is contraindicated for treatment when CrCl is less than 30 mL/min; prophylactic use requires caution with CrCl 30-50 mL/min.