tPA (Alteplase) Stroke Dosing Calculator
Enter the patient weight in kilograms or pounds to instantly compute the alteplase (tPA) dose for acute ischemic stroke. The calculator applies the standard AHA/ASA protocol: 0.9 mg/kg up to a maximum of 90 mg, with 10% delivered as an IV bolus over 1 minute and the remaining 90% infused over 60 minutes. Volume outputs assume the standard 1 mg/mL reconstituted concentration. This tool is for dose-checking only and does not replace clinical judgment or institutional protocols.
What is tPA (alteplase) and why is it used in stroke?
Alteplase is a recombinant tissue plasminogen activator (tPA) that dissolves blood clots by binding to fibrin and converting plasminogen to plasmin, the body's natural clot-dissolving enzyme. In acute ischemic stroke, a blood clot blocks an artery supplying the brain, causing neurons to die rapidly (roughly 1.9 million neurons per minute without treatment). Intravenous alteplase is the only FDA-approved thrombolytic for acute ischemic stroke and remains first-line therapy when the patient presents within 3 hours of symptom onset and has no contraindications. The AHA/ASA also endorse an extended 3-4.5-hour treatment window for selected patients under additional eligibility criteria.
How the dose is calculated
The standard dose is 0.9 mg/kg of actual body weight, with a hard ceiling of 90 mg regardless of weight - this cap applies to all patients at or above 100 kg. Alteplase is reconstituted with Sterile Water for Injection to a concentration of 1 mg/mL (some protocols use 0.5 mg/mL). The total dose is split into two phases: 10% of the total dose is given as a manual IV bolus push over 1 minute, and the remaining 90% is infused via a pump over 60 minutes. For an 80 kg patient: total dose = 72 mg, bolus = 7.2 mg (7.2 mL), infusion = 64.8 mg (64.8 mL) at 64.8 mL/hr.
Treatment windows and eligibility
The 3-hour window from onset (or last known well) has the most robust evidence and carries FDA approval. The AHA/ASA extended window of 3-4.5 hours is acceptable for patients who do not have any of these additional exclusions: age over 80, NIHSS score above 25, use of oral anticoagulants regardless of INR, or a history of both prior stroke and diabetes. Blood pressure must be controlled to below 185/110 mmHg before alteplase is started and maintained below 180/105 mmHg during and after infusion. Patients with hemorrhagic transformation risk from uncontrolled hypertension, recent major surgery, active bleeding, or intracranial hemorrhage on imaging must not receive alteplase.
Administration and monitoring
Alteplase contains no antibacterial preservatives and must be used within 8 hours of reconstitution when stored at 2-30 degrees Celsius. Administer via a dedicated IV line; avoid arterial puncture, IM injections, and invasive procedures during and for 24 hours after infusion. Obtain a baseline non-contrast CT to exclude hemorrhage before dosing. After infusion, admit to a stroke unit or ICU with neurological monitoring every 15 minutes for the first 2 hours, every 30 minutes for hours 2-8, and hourly thereafter. If significant neurological deterioration or suspected intracranial hemorrhage occurs, stop the infusion immediately and obtain urgent CT imaging. The antidote is aminocaproic acid, which inhibits fibrinolysis.
Alteplase dosing by weight (0.9 mg/kg, max 90 mg)
| Weight (kg) | Total dose (mg) | Bolus (mg / mL) | Infusion (mg / mL) | Infusion rate (mL/hr) |
|---|---|---|---|---|
| 40 | 36 | 3.6 / 3.6 | 32.4 / 32.4 | 32.4 |
| 50 | 45 | 4.5 / 4.5 | 40.5 / 40.5 | 40.5 |
| 60 | 54 | 5.4 / 5.4 | 48.6 / 48.6 | 48.6 |
| 70 | 63 | 6.3 / 6.3 | 56.7 / 56.7 | 56.7 |
| 75 | 67.5 | 6.8 / 6.8 | 60.8 / 60.8 | 60.8 |
| 80 | 72 | 7.2 / 7.2 | 64.8 / 64.8 | 64.8 |
| 90 | 81 | 8.1 / 8.1 | 72.9 / 72.9 | 72.9 |
| >=100 | 90 | 9.0 / 9.0 | 81.0 / 81.0 | 81.0 |
Standard 1 mg/mL reconstituted concentration. Bolus is administered over 1 minute; infusion runs over 60 minutes.
Frequently asked questions
What is the maximum dose of alteplase for stroke?
The maximum dose is 90 mg, regardless of patient weight. This cap applies to any patient weighing 100 kg or more. Below 100 kg, the dose is 0.9 mg/kg. For example, a 95 kg patient receives 85.5 mg, while a 105 kg patient also receives 90 mg.
Why is 10% given as a bolus and 90% as an infusion?
The bolus delivers a rapid concentration of alteplase to the clot site, initiating fibrinolysis quickly. The prolonged 60-minute infusion maintains adequate plasma levels to fully dissolve the clot without producing a dangerously high peak concentration that could increase hemorrhage risk. The 10/90 split is the protocol used in all major stroke trials including NINDS and ECASS III.
Can alteplase be used after 4.5 hours from stroke onset?
Generally no. Beyond 4.5 hours the risk of bleeding complications, including symptomatic intracranial hemorrhage, outweighs the benefit of recanalization because penumbral (salvageable) brain tissue is typically lost. In some centers, perfusion imaging (CT perfusion or MRI DWI/FLAIR mismatch) may identify late-window patients who could benefit, but this is not standard practice and falls outside the approved label.
What concentration should alteplase be reconstituted to?
The manufacturer recommends reconstituting to 1 mg/mL using the supplied Sterile Water for Injection. This means a 50 mg vial dissolves in 50 mL and a 100 mg vial in 100 mL. Some institutions further dilute to 0.5 mg/mL; this calculator supports both concentrations. Use the sterile water provided in the kit, not bacteriostatic water, which can denature the enzyme.
What blood pressure is required before giving tPA?
Blood pressure must be reduced to and maintained below 185/110 mmHg before alteplase is initiated. During and for the first 24 hours after infusion, maintain BP below 180/105 mmHg. Agents commonly used to achieve this include labetalol IV, nicardipine IV, or hydralazine IV. Do not give alteplase if BP cannot be safely controlled to these targets.
Is this calculator appropriate for pulmonary embolism (PE)?
No. Alteplase dosing for massive pulmonary embolism uses a different fixed-dose protocol: 100 mg infused over 2 hours (10 mg bolus, 90 mg over 2 hours). The 0.9 mg/kg weight-based calculation on this page applies only to acute ischemic stroke. Use a separate PE dosing reference for that indication.