What is the preferred thrombolytic agent, streptokinase (SK) or urokinase (UK), in the management of ST-elevation myocardial infarction (STEMI)?

Streptokinase vs Urokinase in ST Elevation MI

Neither streptokinase nor urokinase is currently recommended as a first-line thrombolytic agent for STEMI management according to contemporary guidelines, with fibrin-specific agents being preferred.

Current Recommendations for Thrombolytic Therapy in STEMI

Preferred Thrombolytic Agents

Current guidelines from both American College of Cardiology/American Heart Association (ACC/AHA) and European Society of Cardiology (ESC) recommend:

• Primary PCI as the preferred reperfusion strategy when available within 90-120 minutes of first medical contact 1, 2
• When fibrinolysis is necessary, fibrin-specific agents (tenecteplase, alteplase, or reteplase) are recommended over non-specific agents 1, 2

The 2017 ESC guidelines explicitly state: "A fibrin-specific agent (i.e., tenecteplase, alteplase, or reteplase) is recommended" with a Class I, Level B recommendation 1.

When to Use Thrombolytic Therapy

Fibrinolytic therapy should be administered when:

• Primary PCI cannot be performed within 120 minutes of first medical contact 1, 2
• Administered within 30 minutes of first medical contact 2
• Most effective within first 2-3 hours of symptom onset 1

Historical Context of Streptokinase vs Urokinase

Both streptokinase and urokinase are older, non-fibrin-specific thrombolytic agents that have largely been replaced by newer fibrin-specific agents in contemporary practice.

Streptokinase Considerations

• Less expensive than newer agents 3
• Associated with higher rates of allergic reactions
• Requires 60-minute infusion 3
• Cannot be readministered due to antibody formation
• Lower rates of intracranial hemorrhage compared to some newer agents 3

Comparative Efficacy

In the Middle East registry study (2012), streptokinase was associated with higher mortality at both 1-month (4.2% vs 0.8%) and 1-year (3.4% vs 0%) compared to newer thrombolytic agents 4.

Adjunctive Therapy with Thrombolytics

Regardless of the thrombolytic agent used, guidelines recommend:

• Aspirin (162-325 mg loading dose) 1, 2
• Clopidogrel (300 mg loading dose if ≤75 years old) 1
• Anticoagulation until revascularization or hospital discharge (up to 8 days) 1
  • Enoxaparin (preferred over UFH) 1
  • Unfractionated heparin as an alternative 1

Post-Thrombolysis Management

• Transfer to PCI-capable center immediately after fibrinolysis 1
• Rescue PCI indicated if fibrinolysis fails (<50% ST-segment resolution at 60-90 min) 1
• Routine angiography recommended 2-24 hours after successful fibrinolysis 1

Emerging Approaches

Recent research has explored intracoronary thrombolysis as an adjunctive therapy to primary PCI in selected cases with large thrombus burden 5, 6. However, this approach is still investigational and not part of routine care.

Key Pitfalls to Avoid

1. Delayed reperfusion: Time is critical; door-to-needle time should be ≤30 minutes 2
2. Inappropriate patient selection: Absolute contraindications include history of intracranial hemorrhage, significant closed head/facial trauma, uncontrolled hypertension, active bleeding, or suspected aortic dissection 2
3. Overlooking age considerations: Patients ≥75 years have higher risk of intracranial hemorrhage with fibrinolysis 2
4. Failure to transfer: All patients should be transferred to a PCI-capable center after fibrinolysis 1
5. Missing rescue PCI opportunity: When fibrinolysis fails, immediate rescue PCI is indicated 1

In summary, when primary PCI is not available within the recommended timeframe, fibrin-specific agents (tenecteplase, alteplase, or reteplase) are preferred over older agents like streptokinase or urokinase for STEMI management.