Streptokinase in Myocardial Infarction: Indications and Dosing
For acute ST-elevation myocardial infarction (STEMI), streptokinase is indicated when administered within 12 hours of symptom onset (ideally within 3 hours for maximum benefit), and the standard dose is 1.5 million units given intravenously over 30-60 minutes 1.
Indications for Streptokinase in MI
Streptokinase is indicated for patients with:
- ST-segment elevation on ECG or new left bundle branch block
- Symptom onset within 12 hours (strongest benefit within first 3 hours)
- No access to primary PCI or when PCI cannot be performed within 120 minutes of first medical contact
- No absolute contraindications to fibrinolytic therapy
The evidence shows time-dependent mortality reduction, with greatest benefit when administered early. Patients presenting within 1-2 hours of symptom onset may particularly benefit from immediate fibrinolytic therapy rather than waiting for transfer to PCI 1.
Dosing Regimen
Standard dose: 1.5 million units IV over 30-60 minutes 1
This dosing has been validated across multiple trials 2, 3. While some studies have explored lower doses (500,000-750,000 units), the standard 1.5 million unit dose remains the guideline-recommended regimen 1.
Administration Details:
- Infuse over 30-60 minutes
- No bolus required (unlike tPA)
- Administer with aspirin and heparin
- Monitor blood pressure closely during and after infusion
Critical Contraindications
Absolute Contraindications:
- Prior streptokinase use within 6 months (highly antigenic - can cause serious allergic reactions) 1
- Any prior intracranial hemorrhage
- Known intracranial vascular malformation or neoplasm
- Ischemic stroke within 3 months
- Suspected aortic dissection
- Active bleeding or bleeding diathesis
- Significant closed-head trauma within 3 months
- Severe uncontrolled hypertension unresponsive to emergency therapy
Relative Contraindications:
- Hypertension on presentation (SBP >180 or DBP >110 mmHg)
- History of ischemic stroke >3 months ago
- Prolonged CPR (>10 minutes)
- Major surgery within 3 weeks
- Recent internal bleeding (2-4 weeks)
- Pregnancy
- Active peptic ulcer
Key Clinical Considerations
Timing is everything: The PRAGUE-2 trial demonstrated that for patients presenting >3 hours after symptom onset, transfer for PCI resulted in lower mortality (6% vs 15.3%) compared to streptokinase 4. However, for patients presenting within 3 hours, either strategy was equally effective.
Streptokinase vs. Fibrin-Specific Agents: Streptokinase achieves TIMI 2 or 3 flow in 60-68% of patients at 90 minutes, compared to 73-85% with fibrin-specific agents like tPA 1. However, streptokinase remains widely used globally due to cost considerations, particularly in resource-limited settings 5.
Antigenic Properties: Unlike tPA, streptokinase is highly antigenic. Absolutely do not re-administer within 6 months of previous exposure - this can cause life-threatening allergic reactions 1.
Common Pitfalls to Avoid
- Don't delay for coagulation studies if the patient has no recent anticoagulant use - start therapy immediately
- Don't use streptokinase if the patient received it within 6 months - choose an alternative fibrinolytic
- Don't administer if door-to-balloon time can be <120 minutes - primary PCI is superior in this scenario
- Don't forget concomitant antiplatelet and anticoagulation therapy - aspirin and heparin should be given alongside streptokinase
Monitoring and Follow-up
- Monitor for reperfusion arrhythmias (common and expected)
- Watch for bleeding complications, particularly intracranial hemorrhage
- Assess for ST-segment resolution at 90 minutes (≥50% resolution indicates successful reperfusion)
- Consider rescue PCI if reperfusion fails (persistent chest pain and ST elevation) 5, 6
The pharmaco-invasive approach using streptokinase followed by early angiography (if reperfusion fails) has shown comparable outcomes to primary PCI when PCI delays exceed 120 minutes 5.