How long does Alteplase Injection take to work?
Last updated September 7, 2026.
**Alteplase starts breaking down a clot within minutes of the infusion beginning, but it can take hours to days to see how much function comes back.** The exact timing depends on what is being treated. In ischemic stroke, alteplase is given as a short initial dose followed by an infusion over about 60 minutes, and it works best when started as early as possible after symptoms begin. Some people improve while the infusion is still running, while others improve gradually over the following days. When alteplase is used to clear a blocked central line, the catheter is usually tested about 30 minutes after the dose is instilled. Your care team checks blood pressure and neurologic signs often for at least 24 hours, since bleeding risk is higher during that window.
What to do
- Call 911 immediately: Sudden face drooping, arm weakness, or speech trouble means calling emergency services right away, because eligibility for alteplase closes within hours.
- Note the last normal time: Tell the team the exact time symptoms started or when you were last known to be well, since dosing decisions depend on it.
- Expect close monitoring: Frequent blood pressure and neurologic checks for at least 24 hours are routine, not a sign that something went wrong.
- Report bleeding signs: Tell staff about a worsening headache, bleeding gums, blood in urine or stool, or new weakness during or after the infusion.
- Ask about catheter doses: If alteplase is used to unblock a line, ask when flow will be rechecked and whether a second dose is planned.
- Plan the follow-up: Recovery after a stroke continues for weeks, so ask about rehabilitation and what medicines you will take to prevent another clot.
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