**Question:** The only thrombolytic agent approved for the treatment of acute ischemic stroke is -

A. Alteplase (tissue plasminogen activator)
B. Streptokinase
C. Heparin
D. Heparins

**Correct Answer:** A. Alteplase (tissue plasminogen activator)

**Core Concept:**
Acute ischemic stroke is a medical emergency caused by blood vessel blockage, leading to reduced blood flow and oxygen supply to the brain. Thrombolytic agents are medications that dissolve blood clots and restore blood flow to the affected area. Alteplase (tissue plasminogen activator) is the only thrombolytic agent approved for the treatment of acute ischemic stroke, whereas other options are either not specific to stroke or not approved for this indication.

**Why the Correct Answer is Right:**
Alteplase is a recombinant form of human tissue plasminogen activator (tPA), a protein that activates plasmin, an enzyme that breaks down fibrin (the component of blood clots). By breaking down fibrin, alteplase dissolves the blood clot and restores blood flow to the ischemic area, preventing further brain damage and minimizing disability. The effectiveness of alteplase is dose-dependent and time-sensitive, with the "golden window" window of treatment being within 4.5 hours of stroke onset.

**Why Each Wrong Option is Incorrect:**
1. Streptokinase (B) is a plasma protein derived from Streptococcus bacteria. Unlike alteplase, streptokinase lacks specificity and can cause systemic bleeding complications due to its non-selective action on both arterial and venous thrombolysis.
2. Heparins (D) are a class of anticoagulant drugs that inhibit clot formation and prevent clot dissolution, which makes them unsuitable for acute ischemic stroke treatment.
3. Heparin (D) is a broad anticoagulant medication that inhibits clot formation and does not specifically target fibrinolysis like alteplase does.

**Clinical Pearl:**
Timely administration of alteplase within the therapeutic window is crucial for maximizing the effectiveness of thrombolytic therapy in acute ischemic stroke patients. The treatment must be administered by a trained medical professional under close monitoring for potential complications like intracranial hemorrhage, which is more common in the first 4.5 hours after stroke onset.