PDF: EXTEND-IA TNK
(2018)Objective
To compare the efficacy and safety of tenecteplase versus alteplase in achieving early reperfusion prior to endovascular thrombectomy in acute ischemic stroke.
Study Summary
• Tenecteplase was associated with higher early reperfusion rates and improved functional outcomes compared to alteplase.
Intervention
Randomized administration of IV tenecteplase (0.25 mg/kg) vs. IV alteplase (0.9 mg/kg), followed by standard thrombectomy in eligible ischemic stroke patients within 4.5 hours of symptom onset.
Inclusion Criteria
Acute ischemic stroke with large-vessel occlusion (ICA, MCA M1/M2, or basilar artery), within 4.5 hours of onset and eligible for thrombectomy.
Study Design
Arms: Tenecteplase group vs. Alteplase group (both followed by thrombectomy if needed).
Patients per Arm: Tenecteplase: 101, Alteplase: 101
Outcome
• Primary: Substantial reperfusion at initial angiography was higher with tenecteplase (22%) vs. alteplase (10%) (P=0.002 for noninferiority, P=0.03 for superiority); • Functional outcome at 90 days (mRS): median mRS 2 with tenecteplase vs. 3 with alteplase (common OR 1.7, 95% CI 1.0–2.8, P=0.04); • Functionally independent outcome: 64% with tenecteplase vs. 51% with alteplase (P=0.06); • Death: lower with tenecteplase (10%) vs. alteplase (18%) (P=0.049); • Symptomatic intracerebral hemorrhage: 1% in both groups.
Bottom Line
Tenecteplase led to higher rates of early reperfusion and improved functional outcomes compared to alteplase in patients undergoing thrombectomy within 4.5 hours of symptom onset.
Major Points
- EXTEND-IA TNK was the FIRST randomized trial to demonstrate tenecteplase superiority over alteplase before thrombectomy — launching the global shift toward tenecteplase as the preferred thrombolytic for acute stroke.
- 202 patients with LVO (ICA, M1, M2, or basilar) eligible for both IV thrombolysis and thrombectomy within 4.5 hours, randomized at 13 Australian/NZ centers. Primary outcome: substantial early reperfusion (≥50% territory or no thrombus) on initial angiography.
- Tenecteplase DOUBLED early reperfusion: 22% vs 10% (adjusted OR 2.6, 95% CI 1.1–5.9, p=0.02). This means more patients arrived at the cath lab with partially or completely dissolved clots — simplifying the thrombectomy procedure.
- Better 90-day outcomes: median mRS 2 vs 3 (OR 1.7, 95% CI 1.0–2.8, p=0.04). Functional independence (mRS 0–2) trended higher: 64% vs 51% (p=0.06). Mortality trended lower: 10% vs 18% (p=0.08).
- Safety was equivalent or better: sICH was 1% in BOTH groups — identical hemorrhage rates despite higher recanalization, disproving concerns that tenecteplase might increase bleeding risk.
- Practical advantage: tenecteplase is given as a single IV BOLUS over 5–10 seconds (weight-based, 0.25 mg/kg, max 25 mg) — no 1-hour infusion like alteplase. This is transformative for 'drip-and-ship' models where patients need immediate transfer after thrombolysis.
- Tenecteplase 0.25 mg/kg dose was selected — lower than the cardiac dose (0.5 mg/kg) to balance efficacy and safety. This dose became the standard in subsequent trials (AcT, TASTE, NOR-TEST 2).
- Pharmacology advantage: tenecteplase has ~20-minute half-life (vs alteplase's ~4 min), 14× higher fibrin specificity, and 80× greater resistance to PAI-1 inhibition — making it a superior thrombolytic from a pharmacokinetic standpoint.
- Led directly to EXTEND-IA TNK Part 2 (0.25 vs 0.40 mg/kg dose comparison), AcT (Canadian phase 3, positive), and ultimately guideline endorsement of tenecteplase as an acceptable alternative to alteplase (2019 AHA/ASA update).
- Australia/NZ became the first region to adopt tenecteplase as first-line for acute stroke — demonstrating that a single well-designed phase 2 trial can shift global practice when the pharmacologic rationale is strong.
Study Design
- Study Type
- Multicenter, randomized, open-label, blinded-endpoint trial (PROBE design)
- Randomization
- Yes
- Blinding
- Blinded outcome assessment
- Sample Size
- 202
- Follow-up
- 90 days
- Centers
- 13
- Countries
- Australia, New Zealand
Primary Outcome
Definition: Substantial reperfusion (≥50% or no retrievable thrombus) at initial angiographic assessment
| Control | Intervention | HR/OR | P-value |
|---|---|---|---|
| 10% | 22% | - (2–21% difference; OR 2.6 (1.1–5.9)) | 0.02 |
Limitations & Criticisms
- Open-label design with blinded endpoint assessment — awareness of thrombolytic type could influence clinical decisions (e.g., timing of thrombectomy).
- Originally powered for noninferiority, but reported as superiority — the superiority finding (p=0.03 for reperfusion) should be interpreted cautiously as a secondary analysis framework.
- Small sample size (n=202) limits statistical power for secondary clinical outcomes (mRS 0-2 difference did not reach significance, p=0.06).
- Baseline imaging mismatch criteria were removed mid-trial (protocol amendment), changing the enrolled population and raising concerns about selection consistency.
- Single-country trial (Australia) — practice patterns (rapid workflow, high thrombectomy rates) may not generalize to all healthcare systems.
- All patients received thrombolysis AND thrombectomy — cannot determine tenecteplase benefit for patients who do NOT proceed to thrombectomy.
- The 0.25 mg/kg dose was extrapolated from cardiac data; EXTEND-IA TNK Part 2 later showed 0.40 mg/kg offered no additional benefit, but neither dose was compared to no thrombolysis.
- Short enrollment period and relatively small number of centers may introduce site-selection bias toward high-volume stroke centers.
- The primary endpoint (reperfusion on initial angiogram) is a surrogate marker — clinical outcomes (mRS) showed favorable trends but did not all reach significance.
Citation
N Engl J Med 2018;378:1573–1582. DOI:10.1056/NEJMoa1716405