ARIXTRA
Clinical safety rating: caution
Comprehensive clinical and safety monograph for ARIXTRA (ARIXTRA).
Selective factor Xa inhibitor that binds to antithrombin III and enhances its inactivation of factor Xa, thereby inhibiting thrombin formation and reducing clot formation.
| Metabolism | Primarily eliminated unchanged by the kidneys; minimal hepatic metabolism. |
| Excretion | Renal excretion of unchanged drug: 100% of absorbed dose; 77% recovered in urine as unchanged drug, 10% as metabolites. No biliary or fecal elimination of parent drug. |
| Half-life | Terminal elimination half-life: 17-21 hours (mean 18-19 hours) in young adults; prolonged to ~28 hours in elderly. Clinical context: once-daily dosing provides sustained anti-Xa activity. |
| Protein binding | 94% to antithrombin III (ATIII) with low affinity; negligible binding to other plasma proteins. Free fraction: ~6%. |
| Volume of Distribution | Vd: 7-11 L (approx 0.1-0.15 L/kg). Clinical meaning: Indicates limited extravascular distribution, consistent with mainly intravascular space. |
| Bioavailability | Subcutaneous: 100% absolute bioavailability (complete absorption). No oral formulation. Intravenous: 100%. |
| Onset of Action | Subcutaneous: Peak anti-Xa activity at 2-3 hours (onset of action ~1-2 hours). Intravenous: Immediate onset with peak anti-Xa effect in 5-10 minutes. |
| Duration of Action | Subcutaneous: Anti-Xa activity detectable for >24 hours; therapeutic effect lasts ~24 hours (once-daily dosing). Renal impairment prolongs duration. |
2.5 mg subcutaneously once daily for venous thromboembolism prophylaxis; for treatment of deep vein thrombosis or pulmonary embolism: 5 mg (body weight <50 kg), 7.5 mg (50-100 kg), or 10 mg (>100 kg) subcutaneously once daily, after initial parenteral anticoagulation for at least 5 days.
| Dosage form | SOLUTION |
| Renal impairment | Contraindicated if creatinine clearance <30 mL/min; for CrCl 30-50 mL/min, reduce dose to 1.5 mg once daily for prophylaxis and avoid for treatment; no adjustment for CrCl >50 mL/min. |
| Liver impairment | No specific Child-Pugh based dose modifications have been established; use with caution in severe hepatic impairment due to increased bleeding risk. |
| Pediatric use | Not approved for use in pediatric patients; safety and efficacy not established. |
| Geriatric use | No specific dose adjustment required based on age alone; monitor renal function closely due to age-related decline in creatinine clearance. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for ARIXTRA (ARIXTRA).
| Breastfeeding | Unknown if fondaparinux is excreted in human milk. M/P ratio not available. Caution: potential for adverse effects in nursing infant. Use only if benefit outweighs risk. |
| Teratogenic Risk | Fondaparinux (ARIXTRA) is a Factor Xa inhibitor. Animal studies showed no teratogenicity at doses up to 5 times the human dose. No adequate human studies in pregnancy. First trimester: theoretical risk of hemorrhage. Second and third trimesters: risk of bleeding, placental abruption, and fetal hemorrhage. Use only if clearly needed. |
■ FDA Black Box Warning
Spinal/epidural hematomas: Concomitant use with neuraxial anesthesia or spinal puncture increases risk of spinal or epidural hematoma, which can result in long-term or permanent paralysis.
| Serious Effects |
["Severe renal impairment (CrCl <30 mL/min)","Active major bleeding","Bacterial endocarditis","History of heparin-induced thrombocytopenia (HIT) or heparin-induced thrombocytopenia with thrombosis (HITTS)"]
| Precautions | ["Increased risk of hemorrhage","Spinal/epidural hematoma with neuraxial procedures","Renal impairment: Dose adjustment required for CrCl 30–50 mL/min; contraindicated if <30 mL/min","Heparin-induced thrombocytopenia (HIT): Avoid in patients with HIT history","Thrombocytopenia: Monitor platelet counts","Elderly patients: Increased bleeding risk","Low body weight (<50 kg): Increased bleeding risk"] |
| Food/Dietary | No specific food interactions. However, avoid excessive alcohol consumption as it may increase bleeding risk. Patients on warfarin overlap should maintain consistent vitamin K intake (leafy greens). |
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| Fetal Monitoring |
| Monitor maternal anti-Xa activity (though not routine due to lack of correlation). Assess for signs of bleeding (e.g., epistaxis, bruising, hematuria). Fetal monitoring: ultrasonography for growth and placental assessment. Monitor for preterm labor. |
| Fertility Effects | No known direct effects on fertility. In rats, no impairment of fertility at doses up to 5 mg/kg/day. Human data limited. |
| Clinical Pearls | Arixtra (fondaparinux) is a synthetic pentasaccharide that selectively inhibits factor Xa via antithrombin III. It has a half-life of 17-21 hours allowing once-daily dosing. No routine monitoring of aPTT or anti-Xa is required. Use with caution in patients with renal impairment (CrCl <30 mL/min contraindicated; CrCl 30-50 mL/min reduce dose). Reversal agent (andexanet alfa) exists but is not routinely used; protamine does not neutralize fondaparinux. Avoid in patients with active bleeding, bacterial endocarditis, or weight <50 kg (increased bleeding risk). For DVT/PE treatment, administer with warfarin overlap for at least 5 days until INR 2-3. |
| Patient Advice | Take this medication exactly as prescribed, usually once daily by injection under the skin. · Do not stop or change the dose without consulting your doctor; sudden discontinuation may increase clotting risk. · Store vials at room temperature away from light. Do not freeze. · Common side effects include bleeding, bruising at injection site, and anemia. · Seek immediate medical attention if you experience unusual bleeding, coughing up blood, black/tarry stools, or severe headache. · Inform all healthcare providers that you are taking fondaparinux before any surgery or dental procedure. · Avoid aspirin, NSAIDs (e.g., ibuprofen), and other blood thinners unless specifically prescribed by your doctor. · If you miss a dose, take it as soon as remembered on the same day; do not double dose the next day. |