Why does the effectiveness of tPA, a thrombolytic drug for ischemic stroke, diminish significantly after the initial hours following symptom onset?

💡 Explanation

The effectiveness of tPA diminishes because excitotoxicity increases neuronal death in the ischemic penumbra over time, therefore limiting the drug's ability to salvage brain tissue. This occurs because glutamate accumulation overwhelms neurons, rather than edema reduction being the primary factor.

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