Why are thrombolytics contraindicated in ischemic stroke?

October 14, 2025 •

2 min read

Approximately 87% of strokes are ischemic, where a blood clot blocks an artery in the brain, but despite the potential to dissolve clots, thrombolytics are contraindicated in many patients due to a significant risk of converting an ischemic event into a life-threatening hemorrhagic one.

Quick Summary

Thrombolytic drugs carry a substantial risk of causing intracranial hemorrhage in ischemic stroke patients, making them unsuitable for those with recent bleeding, surgery, or uncontrolled hypertension.

Key Points

Hemorrhage Risk: Thrombolytics can cause intracranial hemorrhage, a serious complication where bleeding occurs in the brain.
Vulnerable Vessels: Ischemic stroke damages brain tissue and weakens blood vessels, making them prone to rupture when treated with clot-busting drugs.
Absolute Contraindications: Strict patient exclusion criteria include recent internal bleeding, previous brain hemorrhage, and uncontrolled high blood pressure.
Time is Critical: The benefit of thrombolytics diminishes, and the risk of hemorrhage increases significantly, outside the narrow therapeutic time window (typically 4.5 hours).
CT Scan Mandate: An immediate CT scan is required to rule out a hemorrhagic stroke, as giving thrombolytics to a hemorrhagic stroke patient is fatal.
Anticoagulant Interaction: The use of other anticoagulants or antiplatelet agents increases the bleeding risk associated with thrombolytics.
Pathophysiology: Thrombolytics exacerbate neuroinflammation and disrupt the blood-brain barrier, contributing to the risk of bleeding.

The Core Risk: Intracranial Hemorrhage

The primary concern when considering thrombolytics for ischemic stroke is the risk of intracranial hemorrhage (ICH), or bleeding within the brain. Thrombolytics, also known as 'clot-busters,' dissolve blood clots. While this is beneficial for restoring blood flow blocked by an ischemic stroke, it poses a significant danger in the damaged and weakened blood vessels of the stroke-affected brain. Reperfusion with thrombolytics can cause these fragile vessels to rupture, leading to a hemorrhagic stroke, which is often more severe and potentially fatal.

Pathophysiology of Hemorrhagic Conversion

Hemorrhagic conversion from ischemic stroke is influenced by several factors, including damage to the blood-brain barrier caused by ischemia and the action of thrombolytics.

Specific Contraindications and Risk Factors

Strict criteria are used to determine eligibility for thrombolytic therapy to minimize the risk of ICH.

Absolute Contraindications

Conditions that completely rule out thrombolytic use include:

Prior Intracranial Hemorrhage: Increases the likelihood of another bleed.
Known Structural Cerebral Lesions: Such as AVMs or brain tumors.
Active Internal Bleeding: Non-menstrual.
Recent Surgery or Trauma: Major surgery within 14 days or significant head/facial trauma within 3 months.
Severely Uncontrolled Hypertension: Systolic >185 mmHg or diastolic >110 mmHg before treatment.
Bleeding Disorders: Including low platelet count (<100,000/mm³).
Anticoagulant Use: Including certain oral anticoagulants.

Relative Contraindications and Exclusion Criteria

Other factors requiring careful consideration include minor stroke symptoms, recent gastrointestinal bleeding, pregnancy, or seizure at stroke onset.

Ischemic vs. Hemorrhagic Stroke: A Comparative Overview

Treatments differ based on stroke type. Ischemic stroke is caused by a blockage, while hemorrhagic stroke is caused by bleeding.


Feature	Ischemic Stroke	Hemorrhagic Stroke
Cause	Blood clot blocking an artery	Ruptured blood vessel causing bleeding
Incidence	Accounts for ~87% of all strokes	Accounts for ~13% of all strokes
Treatment Goal	Restore blood flow (e.g., with thrombolytics)	Stop bleeding and relieve pressure
Thrombolytic Use	Potential treatment within a narrow time window	Absolutely contraindicated; would worsen bleeding
Imaging	Crucial to confirm blockage and rule out bleeding	Confirms bleeding, guides treatment to control it

The Critical Role of the Time Window

Timely administration is crucial for thrombolytic effectiveness and safety. The therapeutic window for alteplase is typically up to 4.5 hours from symptom onset, as treating beyond this increases ICH risk.

Diagnostic Imperatives: The CT Scan

A non-contrast CT scan is essential to rule out hemorrhagic stroke, as symptoms are often identical. If bleeding is found, thrombolytics are not given.

Conclusion

Thrombolytics offer potential benefits for acute ischemic stroke but carry a significant risk of intracranial hemorrhage. Patient selection based on medical history, bleeding risk factors, blood pressure, anticoagulant use, and ruling out hemorrhagic stroke via CT scan within the narrow therapeutic window is critical for safe administration.

{Link: Mayo Clinic https://www.mayoclinic.org/diseases-conditions/stroke/diagnosis-treatment/drc-20350119}

Frequently Asked Questions

The primary danger is the risk of intracranial hemorrhage, or bleeding into the brain, which can be fatal. The damaged blood vessels and weakened brain tissue in an ischemic stroke patient are susceptible to rupture when exposed to the clot-dissolving effects of thrombolytics.

A CT scan is performed immediately to rule out a hemorrhagic stroke. Since the symptoms of ischemic and hemorrhagic strokes can be identical, imaging is the only way to differentiate them. Administering thrombolytics to a patient with a brain bleed would be catastrophic.

The therapeutic window is typically up to 4.5 hours from the onset of symptoms, though specific guidelines can vary. After this window, the risk of intracranial hemorrhage increases, and the potential benefits of the drug decrease.

No. Severely uncontrolled hypertension (systolic >185 mmHg or diastolic >110 mmHg) is an absolute contraindication for thrombolytic therapy. High blood pressure significantly increases the risk of bleeding into the brain.

A history of intracranial hemorrhage indicates a predisposition to bleeding in the brain. Giving a thrombolytic would significantly increase the risk of another, potentially fatal, brain hemorrhage.

Other conditions include recent major surgery or head trauma, active internal bleeding, low platelet count, and the use of other anticoagulant medications.

No, only a small percentage of patients receive thrombolytics due to the strict eligibility criteria. Factors like the time window, risk of bleeding, and imaging findings limit the number of candidates.