How many patients need to be treated with prehospital thrombosis treatment, such as enoxaparin (low molecular weight heparin), to see a significant effect or lives saved?

Number Needed to Treat for Prehospital Thrombosis in STEMI

Based on the highest quality evidence, you need to treat approximately 100 patients with prehospital fibrinolytic therapy to prevent one death, with approximately 30 early deaths prevented per 1000 patients treated overall when fibrinolysis is given within 12 hours of symptom onset. 1

Mortality Benefit: The Core Numbers

For fibrinolytic therapy in STEMI (the primary context for prehospital thrombosis treatment):

• Overall NNT = 33 to prevent one death when fibrinolysis is given within 12 hours (30 deaths prevented per 1000 patients) 1
• Early presentation NNT = 50 when treated within 2 hours (20 deaths prevented per 1000 patients) 1
• Late presentation NNT = 50 when treated between 7-12 hours (20 deaths prevented per 1000 patients) 1

The prehospital advantage specifically:

• Prehospital fibrinolysis reduces early mortality by 17% compared to in-hospital administration 1
• Meta-analysis of 22 trials showed substantially larger mortality reduction with earlier treatment, with the greatest benefit in patients treated within the first 2 hours 1

Adjunctive Anticoagulation: Additional Benefits

When enoxaparin is added to fibrinolytic therapy (the specific "prehospital thrombosis" context you're asking about):

ExTRACT-TIMI 25 Trial Results (n=20,506):

• Primary endpoint (death or nonfatal MI): 9.9% with enoxaparin vs 12.0% with UFH 1
• Absolute risk reduction: 2.1% 1
• NNT = 48 to prevent one death or MI at 30 days 1
• Net clinical benefit NNT = 20 (death, MI complication, or major bleeding): 10% with enoxaparin vs 15% with UFH 1

For Medical Inpatients (VTE prophylaxis context):

• NNT for VTE = 470 (95% CI 278-1413) 2
• NNT for mortality = 77 (95% CI 55-130) 2

Critical Time-Dependent Factors

The NNT improves dramatically with earlier treatment:

• Patients treated within 2 hours have much larger absolute benefit than those treated later 1
• Pre-hospital initiation of fibrinolytic treatment is recommended when this reperfusion strategy is indicated (Class IIa, Level A) 1
• Analysis of >6000 patients showed 17% reduction in early mortality with pre-hospital vs in-hospital fibrinolysis 1

Important Caveats and Trade-offs

Bleeding risk considerations:

• Major bleeding increases with enoxaparin: 2.1% vs 1.4% with UFH 1
• NNH for major bleeding = 143 1
• In elderly patients (≥75 years), prehospital enoxaparin at standard doses significantly increased intracranial hemorrhage in ASSENT-3 PLUS 1
• Age-adjusted dosing is mandatory: No IV bolus and 0.75 mg/kg SC (max 75 mg) for first two doses in patients ≥75 years 1

Renal impairment adjustments:

• Creatinine clearance <30 mL/min requires dosing every 24 hours instead of every 12 hours 1
• Failure to adjust increases bleeding risk substantially 1

Practical Algorithm for Prehospital Thrombosis Treatment

Step 1: Confirm STEMI and timing

• Symptom onset <12 hours 1
• If <2 hours with large infarct and low bleeding risk, consider fibrinolysis if PCI delay >90 minutes 1
• If 2-12 hours, consider fibrinolysis if PCI delay >120 minutes 1

Step 2: Assess bleeding risk and contraindications

• Age ≥75 years = higher bleeding risk, requires dose adjustment 1
• Renal impairment (CrCl <30) = requires dose adjustment 1
• Prior intracranial hemorrhage = absolute contraindication 1

Step 3: Initiate fibrinolytic + anticoagulation

• Fibrin-specific agent preferred (tenecteplase, alteplase, reteplase) 1
• Enoxaparin dosing for age <75 years: 30 mg IV bolus, then 1 mg/kg SC every 12 hours (max 100 mg first two doses) 1
• Enoxaparin dosing for age ≥75 years: NO IV bolus, 0.75 mg/kg SC every 12 hours (max 75 mg first two doses) 1
• Continue until hospital discharge or maximum 8 days 1

Step 4: Add antiplatelet therapy

• Aspirin 150-325 mg chewed (or 250-500 mg IV) 1
• Clopidogrel 75 mg daily (no loading dose in elderly) 1

Common Pitfalls to Avoid

• Using standard enoxaparin doses in elderly patients: ASSENT-3 PLUS showed significant increase in intracranial hemorrhage with standard dosing in patients ≥75 years 1
• Failing to adjust for renal impairment: Enoxaparin accumulates with CrCl <30 mL/min, dramatically increasing bleeding risk 1
• Switching between enoxaparin and UFH: Increases bleeding risk and should be avoided 1
• Delaying prehospital fibrinolysis when indicated: Every 30-minute delay reduces benefit; 17% mortality reduction with prehospital vs in-hospital administration 1
• Using prasugrel or ticagrelor with fibrinolysis: These have not been studied and should not be given 1