Final answer:
Tissue plasminogen activator (tPA) is the first-line treatment for ischemic stroke if administered within 4.5 hours, as it helps dissolve the clot and restore blood flow to the brain.
Step-by-step explanation:
The treatment of an ischemic stroke when initiated within 4.5 hours of stroke onset is focused on quickly restoring blood flow to the brain. One of the first-line treatments in this setting is the administration of a thrombolytic agent, namely Tissue plasminogen activator (tPA). tPA is an enzyme that facilitates the breakdown of clots by converting plasminogen to plasmin, hence it is critical to administer it within the therapeutic time window to improve prognosis and reduce the risk of permanent brain damage. Aspirin, warfarin, and clopidogrel are not the primary treatments within this early period, as they may be used for secondary prevention or in different phases of stroke management.