A 58-year-old man with acute onset dyspnea and pleuritic chest pain is diagnosed with acute pulmonary embolism on CT pulmonary angiography. He has no contraindications to anticoagulation. What is the drug of choice for initial anticoagulation in this patient?

Question

Accepted Answer

D. Unfractionated heparin (UFH). ## Initial Anticoagulation in Acute Pulmonary Embolism

**Key Point:** Unfractionated heparin (UFH) is the first-line anticoagulant for acute PE because it has the shortest half-life, is reversible with protamine, and allows rapid dose adjustment—critical in hemodynamically unstable patients who may require thrombolysis or embolectomy.

### Mechanism of UFH in PE Management

UFH works by:
1. Potentiating antithrombin III
2. Inhibiting factors IIa and Xa
3. Preventing thrombus propagation and new clot formation
4. Allowing time for endogenous fibrinolysis

### Why UFH is Preferred Over Alternatives

| Feature | UFH | LMWH | Warfarin | Aspirin |
|---------|-----|------|----------|----------|
| **Onset** | Immediate (IV) | 3–4 hrs (SC) | 48–72 hrs | No anticoagulant effect |
| **Reversibility** | Yes (protamine) | Partial | No (takes days) | No |
| **Hemodynamic instability** | Ideal | Relative CI | Contraindicated | Inadequate |
| **Thrombolysis-ready** | Yes | Requires washout | No | No |
| **Monitoring** | aPTT-guided | Not needed | INR-guided | Not applicable |

**High-Yield:** In hemodynamically unstable PE (shock, RV dysfunction), UFH is mandatory because:
- It can be rapidly reversed if bleeding occurs during thrombolysis
- It allows immediate escalation to systemic thrombolysis or embolectomy
- LMWH cannot be rapidly reversed and is contraindicated in shock

**Clinical Pearl:** The target aPTT for PE is 1.5–2.5 × control (or 60–100 seconds), achieved with a bolus of 80 units/kg IV followed by 18 units/kg/hr infusion.

### Transition to Warfarin

Warfarin is started concurrently (day 1) but takes 48–72 hours to achieve therapeutic INR (2–3). UFH is continued until INR is therapeutic for ≥24 hours (overlap period typically 5–7 days).

**Mnemonic: HEPARIN FIRST** — **H**emodynamic instability, **E**arly reversibility, **P**erfect for thrombolysis, **A**djustable dosing, **R**apid onset, **I**ntermediate duration, **N**eeds monitoring.

[cite:Harrison 21e Ch 297]

Answer

A. Clopidogrel

Answer

B. Warfarin

Answer

C. Aspirin

A 58-year-old man with acute onset dyspnea and pleuritic chest pain is diagnosed with acute pulmonary embolism on CT pulmonary angiography. He has no contraindications to anticoagulation. What is the drug of choice for initial anticoagulation in this patient?

Explanation

Initial Anticoagulation in Acute Pulmonary Embolism

Mechanism of UFH in PE Management

Why UFH is Preferred Over Alternatives

Transition to Warfarin

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Feature	UFH	LMWH	Warfarin	Aspirin
Onset	Immediate (IV)	3–4 hrs (SC)	48–72 hrs	No anticoagulant effect
Reversibility	Yes (protamine)	Partial	No (takes days)	No
Hemodynamic instability	Ideal	Relative CI	Contraindicated	Inadequate
Thrombolysis-ready	Yes	Requires washout	No	No
Monitoring	aPTT-guided	Not needed	INR-guided	Not applicable