What is the recommended intravenous alteplase (tPA) dose and contraindications for an acute posterior‑circulation ischemic stroke presenting within 4.5 hours?

Thrombolysis in Posterior Circulation Stroke

For acute posterior circulation ischemic stroke presenting within 4.5 hours, administer intravenous alteplase at the standard dose of 0.9 mg/kg (maximum 90 mg) with 10% given as an IV bolus over 1 minute, followed by the remaining 90% infused over 60 minutes, using the same eligibility criteria and contraindications as anterior circulation strokes. 1, 2

Standard Dosing Protocol

• The dose is 0.9 mg/kg body weight with an absolute maximum of 90 mg total, regardless of stroke location. 1, 2, 3
• Administer 10% of the total calculated dose (0.09 mg/kg) as an IV push over exactly 1 minute. 2, 3
• Infuse the remaining 90% of the dose (0.81 mg/kg) continuously over 60 minutes. 2, 3
• No dose adjustment is required for posterior circulation strokes—use the identical protocol as for anterior circulation. 1, 4

Time Window Eligibility

0-3 Hour Window

• All patients meeting NINDS criteria should receive alteplase within 3 hours of symptom onset, including those with posterior circulation strokes. 1, 3
• Age >80 years is NOT a contraindication in the 0-3 hour window. 1, 3
• Severe stroke (NIHSS >25) is NOT a contraindication in the 0-3 hour window. 1, 3
• Prior use of single or dual antiplatelet therapy is NOT a contraindication. 1, 3

3-4.5 Hour Extended Window

• Alteplase may be administered between 3-4.5 hours if ECASS III criteria are met. 1, 2, 3
• Additional exclusions in the 3-4.5 hour window include: age >80 years, any oral anticoagulant use (regardless of INR), NIHSS >25, or combined history of diabetes AND prior stroke. 1, 2, 3

Evidence Supporting Posterior Circulation Treatment

• Intravenous thrombolysis is appropriate as first-line therapy for posterior circulation stroke, with the same benefit-to-risk profile as anterior circulation strokes. 1
• Patients with posterior circulation stroke treated with alteplase within 3 hours benefit more than those treated between 3-4.5 hours, with significantly lower NIHSS scores at 24 hours post-treatment. 4
• In one retrospective study of 140 posterior circulation stroke patients, those with mild strokes (NIHSS ≤3) treated within 3 hours showed a 53.5% improvement rate versus 33.6% in more severe strokes. 4

Mandatory Pre-Treatment Requirements

• Perform immediate non-contrast CT or MRI to exclude intracranial hemorrhage—this is the only mandatory imaging before alteplase. 1, 2, 3
• Check capillary blood glucose at bedside; glucose must be >50 mg/dL (>3.3 mmol/L). 1, 2, 3
• Lower blood pressure to <185/110 mmHg before initiating alteplase using antihypertensive agents. 1, 2, 3
• Confirm blood pressure stability before drug administration. 1, 2
• Do NOT delay alteplase for other laboratory results (CBC, INR, PTT, creatinine)—only glucose is mandatory. 2, 3

Absolute Contraindications

• Intracranial hemorrhage on initial CT scan. 1, 3
• Unclear or unwitnessed symptom onset with last-known-well time exceeding the applicable window (>3 hours for 0-3h window, >4.5 hours for extended window). 1, 3
• Extensive hypoattenuation (obvious hypodensity) representing irreversible injury on CT. 1, 3
• Prior ischemic stroke within the preceding 3 months. 1, 3
• Severe head trauma within the preceding 3 months. 1, 3
• History of intracranial hemorrhage. 1, 3
• Intracranial or intraspinal surgery within the prior 3 months. 1, 3
• Symptoms and signs most consistent with subarachnoid hemorrhage. 1, 3
• Structural GI malignancy or GI bleeding within 21 days. 1, 3
• Platelets <100,000/mm³, INR >1.7, aPTT >40 seconds, or PT >15 seconds. 1

Post-Administration Management

• Monitor blood pressure every 15 minutes for the first 2 hours, every 30 minutes for the next 6 hours, then hourly up to 24 hours. 3
• Maintain blood pressure ≤180/105 mmHg for 24 hours after alteplase. 2, 3
• Assess neurological status every 15 minutes during infusion, every 30 minutes for 6 hours, then hourly until 24 hours. 3
• If severe headache, acute hypertension, nausea, or vomiting occur, stop the infusion immediately and obtain emergent CT. 3
• Avoid all antithrombotic agents (aspirin, anticoagulants) for 24 hours after alteplase. 3, 5
• Obtain follow-up CT at 24 hours before starting antiplatelet or anticoagulant therapy. 3

Integration with Endovascular Therapy

• If large-vessel occlusion is suspected (including basilar artery), obtain CTA from aortic arch to vertex immediately after non-contrast CT. 3
• Do NOT delay IV alteplase while obtaining vascular imaging or assessing for mechanical thrombectomy eligibility. 1, 3
• Administer IV alteplase even when the patient is being evaluated for or will undergo mechanical thrombectomy. 1, 3
• Do NOT wait to assess response to IV thrombolysis before proceeding to catheter angiography for thrombectomy. 1, 3

Critical Pitfalls to Avoid

• Never use the myocardial infarction dosing protocol (accelerated dosing)—this is a potentially harmful error specific to stroke treatment. 2
• Do not exclude patients with posterior circulation strokes from thrombolysis based on location alone—they derive similar benefit to anterior circulation strokes. 1, 4
• Do not withhold alteplase from patients >80 years old presenting within 0-3 hours; age is only an exclusion in the 3-4.5 hour window. 1, 2, 3
• Do not delay treatment to obtain complete laboratory panels beyond glucose—time-to-treatment is the strongest predictor of outcome. 1, 2, 3
• Earlier treatment yields exponentially better outcomes; every 15-minute delay reduces the probability of favorable functional outcome. 1, 3