Injectable Blood Thinners
Injectable anticoagulants include unfractionated heparin (UFH), low-molecular-weight heparins (LMWHs) such as enoxaparin, dalteparin, and tinzaparin, fondaparinux, direct thrombin inhibitors including hirudin, bivalirudin, and argatroban, and danaparoid. 1
Low-Molecular-Weight Heparins (LMWHs)
The most commonly used injectable anticoagulants are the LMWHs, which have largely replaced unfractionated heparin for many indications due to superior pharmacokinetic properties 1:
FDA-Approved LMWHs in the United States
- Enoxaparin: Approved for both VTE prophylaxis and immediate treatment, as well as acute coronary syndromes 1, 2
- Dalteparin: Approved for VTE prophylaxis and extended treatment of symptomatic VTE in cancer patients 1, 3
- Tinzaparin: Currently approved only for immediate VTE treatment 1
Additional LMWHs Available Internationally
- Nadroparin: Used in Europe and Canada 1
- Reviparin: Available in select countries 1, 4
- Bemiparin, Certoparin, Parnaparin: Approved in various international markets 4
Unfractionated Heparin (UFH)
- Standard heparin: Administered intravenously or subcutaneously, requires monitoring with activated partial thromboplastin time (APTT) 1
- Molecular weight range: 3,000 to 30,000 daltons 5
- Requires continuous IV infusion for therapeutic anticoagulation with frequent laboratory monitoring 6, 7
Synthetic Pentasaccharide
- Fondaparinux: A synthetic pentasaccharide that selectively inhibits Factor Xa through antithrombin-dependent mechanisms 1
- Administered once daily subcutaneously in fixed doses without coagulation monitoring 1
- Complete bioavailability and longer half-life than LMWHs 1
- Lower risk of heparin-induced thrombocytopenia (HIT) and osteoporosis compared to heparin 1
Direct Thrombin Inhibitors
These agents are primarily used as alternatives to heparin in patients with HIT 1:
- Hirudin: Direct thrombin inhibitor 1
- Bivalirudin: Used particularly in percutaneous coronary interventions 1
- Argatroban: Alternative for patients with HIT 1
Other Injectable Anticoagulants
- Danaparoid: A heparinoid approved as an alternative to heparin in patients with HIT 1
Key Advantages of LMWHs Over Unfractionated Heparin
LMWHs have become the preferred injectable anticoagulants for most indications due to several critical advantages 1:
- Predictable dose-response: Approximately 90% bioavailability after subcutaneous injection eliminates need for routine monitoring 1
- Longer half-life: 3-6 hours allows once or twice daily dosing 1
- Lower bleeding risk: Reduced major bleeding compared to UFH for equivalent antithrombotic effect 1, 6, 4
- Reduced HIT risk: Decreased binding to platelets and platelet factor 4 1
- Lower osteoporosis risk: Reduced binding to osteoblasts 1
- Outpatient administration: Enables home treatment of conditions like DVT 1, 6
Important Clinical Caveat
LMWHs are not interchangeable on a unit-for-unit basis because they are prepared using different depolymerization methods, resulting in distinct pharmacokinetic properties, anti-Xa to anti-IIa ratios, and dosing regimens 1, 2. Each LMWH must be dosed according to its specific FDA-approved regimen 1.