tPA is given through an IV line, with a small portion pushed quickly into the vein as an initial dose and the rest slowly dripped in over one hour. The entire process happens in a hospital, typically in an emergency department or stroke unit, and the drug must be given within a narrow time window to be effective. Here’s what the full process looks like from start to finish.
The Time Window for Treatment
For ischemic stroke, tPA must be given within 4.5 hours of when symptoms first appeared. The earlier it’s administered, the better the outcome, so hospital teams work to start treatment as fast as possible rather than waiting to use the full window. Current American Heart Association guidelines emphasize avoiding delays from additional imaging when the diagnosis is clear.
In select cases where brain imaging shows tissue that can still be saved, treatment may be considered up to 9 hours from the last time the patient was known to be symptom-free. This extended window applies to patients who wake up with stroke symptoms or arrive later, but only when advanced perfusion imaging confirms there’s still salvageable brain tissue.
Dosing Based on Body Weight
The standard stroke dose is 0.9 mg per kilogram of body weight, capped at a maximum of 90 mg for anyone weighing 100 kg (about 220 pounds) or more. A 70 kg person, for example, would receive 63 mg total. Getting the weight right matters, since too much increases bleeding risk and too little may not dissolve the clot effectively. Hospital staff estimate or measure weight quickly as part of the preparation process.
How the IV Infusion Works
Once the dose is calculated, 10% of it is given as a bolus, meaning it’s pushed directly into the IV over about one minute. This delivers an immediate burst of the clot-dissolving drug into the bloodstream. The remaining 90% is then infused slowly through an IV pump over 60 minutes.
For that same 70 kg patient receiving 63 mg total, the bolus would be 6.3 mg pushed over one minute, followed by 56.7 mg dripped steadily over the next hour. During and after the infusion, the medical team closely monitors blood pressure, neurological status, and any signs of bleeding.
How the Drug Is Prepared
tPA comes as a dry powder that must be mixed with sterile water before use. The powder is available in 50 mg and 100 mg vials, each paired with its own vial of sterile water. Staff mix them using specific transfer devices, then gently swirl (never shake) the vial until the powder dissolves. Some foaming is normal and settles on its own after a few minutes.
The mixed solution can be given at full strength or diluted further with saline or dextrose. Once reconstituted, it must be used within 8 hours because it contains no preservatives. In practice, most doses are prepared and administered within minutes in an emergency setting.
Who Can and Cannot Receive tPA
Before administration, the medical team runs through a screening checklist. Several conditions rule out tPA entirely because the drug works by dissolving clots, which means it also increases the risk of dangerous bleeding anywhere in the body.
You won’t be eligible if you have:
- Blood pressure above 185/110 that can’t be brought down safely
- Any history of bleeding in the brain
- A brain tumor, aneurysm, or abnormal blood vessel formation in the brain
- A significant head injury or stroke within the past 3 months
- Active internal bleeding
- Very low platelet counts or blood that doesn’t clot normally
- Recent brain or spinal surgery
- Blood sugar below 50 mg/dL
- A brain scan showing a very large area of damage (more than one-third of a hemisphere)
Certain blood-thinning medications also disqualify patients, particularly anticoagulants that push clotting tests above safe thresholds. If you’ve received heparin in the past 48 hours and your clotting time is elevated, tPA won’t be given.
Some situations fall into a gray area where the medical team weighs risks against benefits on a case-by-case basis. These include pregnancy, a seizure at the time of the stroke, major surgery within the past two weeks, and symptoms that are very mild or already improving on their own.
Blood Pressure Management During Treatment
Blood pressure must be below 185/110 before the infusion starts. If it’s higher, the team will use medications to bring it down and confirm it’s stable at the lower level before beginning tPA. Once treatment starts, blood pressure needs to stay below 180/105 for at least the first 24 hours. This tight control reduces the risk of bleeding complications in the brain.
Risks During and After Administration
Bleeding is the most significant risk. Because tPA dissolves clots throughout the body, it can cause hemorrhage in the brain, gastrointestinal tract, or urinary system. The brain is the primary concern, which is why neurological checks happen frequently during and after the infusion.
A less common side effect is angioedema, a rapid swelling of the tongue, lips, or throat that occurs in roughly 0.2% to 8% of stroke patients who receive the drug. Men are about 3.3 times more likely to develop this reaction than women. People who take ACE inhibitors for blood pressure, or who have a history of allergic swelling, face higher risk. Strokes affecting the frontal lobe of the brain also appear to increase susceptibility.
The medical team monitors closely for both bleeding and swelling throughout the infusion and for hours afterward. If either complication develops, the infusion is stopped immediately and the team intervenes.
tPA for Other Conditions
While stroke is the most well-known use, tPA is also approved for treating massive pulmonary embolism (a large blood clot in the lungs) and heart attack. The dosing and infusion protocols differ for each condition. For pulmonary embolism, the total dose is higher and the infusion time is typically shorter than for stroke. The core principle remains the same: delivering the drug intravenously to dissolve a life-threatening clot. A newer alternative called tenecteplase is now endorsed alongside tPA for stroke treatment, offering a simpler single-dose injection rather than a one-hour infusion.