## First-Line Anticoagulation in Acute PE **Key Point:** Unfractionated heparin (UFH) is the gold standard for initial anticoagulation in acute pulmonary embolism, particularly in hemodynamically stable patients with normal renal function. ### Mechanism of Action UFH inhibits factors IIa and Xa through antithrombin III, providing rapid onset of anticoagulation with a half-life of 60–90 minutes, allowing quick reversal if needed. ### Why UFH is Preferred in Acute PE | Feature | UFH | LMWH | Fondaparinux | DOACs | |---------|-----|------|--------------|-------| | Onset | Immediate (IV) | 2–4 hrs | 2–4 hrs | 2–4 hrs | | Reversibility | Yes (protamine) | Partial | No | No | | Renal clearance | Hepatic | Renal | Renal | Renal | | Monitoring | aPTT required | Not needed | Not needed | Not needed | | Use in PE | Gold standard | Alternative | Alternative | Alternative | | ICU/unstable | Preferred | Avoid | Avoid | Avoid | **High-Yield:** UFH is the ONLY anticoagulant that can be rapidly reversed with protamine sulfate — critical if the patient deteriorates or requires emergency surgery. ### Clinical Pearl In hemodynamically unstable PE (shock, RV dysfunction), UFH is mandatory because: - Rapid reversibility if thrombolysis is needed - Can be used in renal failure (hepatic metabolism) - Allows aPTT monitoring for dose titration - Permits rapid IV bolus and infusion adjustment ### Dosing - **Loading dose:** 80 units/kg IV bolus - **Maintenance:** 18 units/kg/hr IV infusion - **Target aPTT:** 1.5–2.5 × control (or 50–80 seconds) **Tip:** Always check baseline aPTT, PT, platelet count, and creatinine before starting UFH. Monitor for heparin-induced thrombocytopenia (HIT) — platelet count should be checked at baseline and day 3–5. [cite:Harrison 21e Ch 297]
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