Understanding Streptokinase and Its Risks
Streptokinase is a thrombolytic, or "clot-busting," medication derived from streptococcal bacteria [1.7.5]. Its primary function is to dissolve blood clots in conditions like ST-elevation myocardial infarction (STEMI), pulmonary embolism (PE), and deep vein thrombosis (DVT) [1.3.6]. It works by forming a complex with plasminogen, which activates it into plasmin. Plasmin is an enzyme that degrades the fibrin matrix of a thrombus, effectively breaking it down [1.7.1, 1.7.2]. However, this process is not fibrin-specific, meaning it also breaks down circulating fibrinogen and other proteins, creating a systemic lytic state that significantly increases the risk of bleeding throughout the body [1.7.3, 1.7.6]. Because streptokinase is a bacterial protein, it is antigenic and can cause allergic reactions, especially upon re-exposure [1.6.5]. For this reason, knowing the specific situations where its use is contraindicated is essential for patient safety.
Absolute Contraindications: When Streptokinase Must Be Avoided
Absolute contraindications are conditions where the administration of streptokinase poses a life-threatening risk that far outweighs any potential benefit [1.2.8]. The primary concern is intracranial hemorrhage (ICH), which can be fatal. According to guidelines from bodies like the American Heart Association (AHA), these are situations where streptokinase should not be used [1.4.1, 1.2.3].
Key Absolute Contraindications Include:
- Any prior Intracranial Hemorrhage (ICH): A history of bleeding in the brain at any point is a top-level contraindication [1.2.3, 1.4.1].
- Known Structural Cerebral Vascular Lesion: This includes conditions like arteriovenous malformations (AVMs) or aneurysms [1.2.3, 1.3.6].
- Known Malignant Intracranial Neoplasm: Brain tumors, whether primary or metastatic, increase the risk of bleeding [1.2.3, 1.4.1].
- Ischemic Stroke within the Last 3 Months: The risk of hemorrhagic conversion of the stroke is unacceptably high [1.2.3, 1.4.1]. An exception may be an acute ischemic stroke within 3-4.5 hours, though newer agents are often preferred [1.2.3].
- Suspected Aortic Dissection: Thrombolysis can cause the dissection to rupture, leading to catastrophic hemorrhage [1.2.3, 1.4.1].
- Active Bleeding or Bleeding Diathesis: This excludes menstruation. Any ongoing internal bleeding is an absolute contraindication [1.2.3, 1.3.1].
- Significant Closed-Head or Facial Trauma within 3 Months: This includes any recent major trauma to the head or face [1.2.3, 1.4.1].
- Recent Intracranial or Intraspinal Surgery: Surgery within the brain or on the spine within the last 2 months presents a high risk [1.2.2, 1.2.3].
- Severe Uncontrolled Hypertension: Blood pressure that is unresponsive to emergency therapy (e.g., SBP >180 mmHg or DBP >110 mmHg) significantly raises the risk of ICH [1.3.3, 1.4.5].
- Prior Treatment with Streptokinase: Previous exposure to streptokinase (typically within the last 6-12 months) is a specific contraindication due to the presence of antibodies that can cause severe allergic reactions or neutralize the drug's effect [1.2.3, 1.3.2].
Relative Contraindications: Use with Extreme Caution
Relative contraindications are conditions where the risk of using streptokinase is increased, and the decision to proceed must be based on a careful risk-versus-benefit analysis for the individual patient [1.2.8]. In these cases, the potential for saving a life by dissolving a clot in a major artery might outweigh the risks.
Common Relative Contraindications:
- Severe or Poorly Controlled Chronic Hypertension: A history of high blood pressure, even if currently managed [1.2.5, 1.3.3].
- Major Surgery or Serious Trauma within the Last 3 Weeks: This includes traumatic or prolonged (>10 minutes) CPR [1.2.5, 1.3.3].
- Recent Internal Bleeding (within 2 to 4 weeks): For example, gastrointestinal bleeding [1.2.5].
- Noncompressible Vascular Punctures: Recent punctures of vessels that cannot be easily compressed if they start bleeding [1.3.3].
- Active Peptic Ulcer: Increased risk of severe GI bleeding [1.2.5, 1.3.3].
- Pregnancy: Risk of maternal bleeding and potential effects on the fetus [1.2.5, 1.3.1].
- Current Use of Anticoagulants: An elevated International Normalized Ratio (INR) >1.7 or Prothrombin Time (PT) >15 seconds suggests a higher baseline bleeding risk [1.2.5].
- Advanced Age (>75 years): Elderly patients are generally at a higher risk for hemorrhagic complications [1.3.1].
- Diabetic Hemorrhagic Retinopathy: A condition that predisposes to bleeding in the eye [1.3.1].
Comparison of Thrombolytic Agents
Streptokinase is a first-generation thrombolytic. Newer, fibrin-specific agents like Alteplase (tPA) and Tenecteplase (TNK) are often preferred, especially in high-income countries, due to a different risk profile.
| Feature | Streptokinase | Alteplase (tPA) | Tenecteplase (TNK) |
|---|---|---|---|
| Mechanism | Non-fibrin-specific, binds plasminogen systemically [1.7.6] | Fibrin-specific, preferentially activates plasminogen at the clot site [1.7.3] | Fibrin-specific with a longer half-life than tPA [1.5.4] |
| Antigenicity | High (bacterial origin), risk of allergic reaction, cannot be re-administered soon [1.6.5] | Low (recombinant human protein) | Low (recombinant human protein) |
| Risk of Hypotension | Higher risk due to bradykinin release [1.7.6, 1.5.4] | Lower risk | Lower risk [1.5.4] |
| Risk of ICH | Lower risk compared to accelerated alteplase in some studies [1.5.3] | Higher risk than streptokinase in some large trials [1.5.3] | Similar or lower risk compared to alteplase |
| Administration | 60-minute infusion [1.2.4] | 90-minute accelerated infusion or other protocols [1.5.5] | Single IV bolus over 5 seconds |
| Cost | Low-cost [1.6.4] | Higher cost | Higher cost |
Conclusion
The decision to use streptokinase is a high-stakes clinical judgment that requires a thorough evaluation of the patient's history and current condition. While it can be a life-saving intervention for heart attacks and pulmonary embolisms, its powerful systemic effect and potential for severe complications, especially bleeding and allergic reactions, demand strict adherence to its contraindications. The existence of absolute contraindications like prior intracranial hemorrhage or recent major trauma means the drug must be withheld. For relative contraindications, the clinical team must carefully weigh whether the benefit of dissolving a life-threatening clot justifies the significant risks involved. With the availability of newer, more specific thrombolytics, the role of streptokinase has evolved, but understanding when not to use it remains a fundamental principle of safe medical practice.
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult with a qualified healthcare professional for diagnosis and treatment. For more authoritative information, please refer to guidelines from professional bodies such as the American Heart Association.
