A 72-year-old woman with a mechanical mitral valve prosthesis and a history of thromboembolism is admitted with acute deep vein thrombosis of the right lower limb. She is currently on warfarin (INR 2.5). What is the drug of choice for acute DVT management in this patient?

Explanation

## Acute DVT Management in Anticoagulated Patients **Key Point:** Unfractionated heparin (UFH) is the drug of choice for acute DVT in patients already on warfarin because it provides rapid anticoagulation with a short half-life, allowing easy reversal if bleeding occurs, and is the safest option in patients with mechanical heart valves. ## Rationale for UFH in This Clinical Context 1. **Immediate anticoagulation:** UFH has an onset of action within minutes (IV bolus), whereas warfarin takes 48–72 hours to achieve full effect. 2. **Reversibility:** UFH can be rapidly reversed with protamine sulfate if bleeding complications arise. 3. **Mechanical valve consideration:** Patients with mechanical prostheses require bridging anticoagulation during any transition; UFH is the standard bridge. 4. **Current warfarin inadequacy:** An INR of 2.5 on warfarin is therapeutic for most indications but may be insufficient for acute thrombotic events; UFH provides additional immediate protection. ## Comparison of Anticoagulants in Acute DVT | Agent | Onset | Half-Life | Reversibility | Use in Mechanical Valve | First-Line in Acute DVT | | --- | --- | --- | --- | --- | --- | | **UFH** | Minutes (IV) | 60–90 min | Yes (protamine) | **Yes** | **Yes** | | LMWH | 3–4 hours | 4–6 hours | Partial (protamine) | Caution; limited data | Alternative if no mechanical valve | | Warfarin | 48–72 hours | 36–42 hours | Yes (FFP, vitamin K) | Yes (for maintenance) | No; too slow for acute DVT | | Fondaparinux | 2–3 hours | 17–21 hours | No | Contraindicated | Not preferred; no reversal agent | ## Clinical Pearl **High-Yield:** In patients with mechanical heart valves, UFH is mandatory for bridging because it is the only parenteral anticoagulant with proven safety and rapid reversibility in this high-risk population. Fondaparinux and LMWH lack adequate data in mechanical valve patients. ## Management Algorithm ```mermaid flowchart TD A[Acute DVT diagnosed]:::outcome --> B{Patient on warfarin?}:::decision B -->|Yes| C{Mechanical valve?}:::decision B -->|No| D[Start UFH or LMWH]:::action C -->|Yes| E[UFH mandatory]:::action C -->|No| F[UFH or LMWH acceptable]:::action E --> G[Bolus 80 IU/kg IV, then 18 IU/kg/hr infusion]:::action F --> H[Monitor aPTT target 1.5-2.5x baseline]:::action G --> I[Continue warfarin; overlap until INR 2-3 for 24 hrs]:::action ``` **Dosing:** UFH bolus 80 IU/kg IV, followed by continuous infusion at 18 IU/kg/hr, titrated to aPTT 1.5–2.5 times baseline (typically 60–80 seconds). [cite:Harrison 21e Ch 297]