Tenecteplase Beats Low-Dose Alteplase at Opening Blocked Brain Arteries Before Surgery

Stroke caused by large-vessel occlusion (LVO) demands both speed and effective clot dissolution before mechanical thrombectomy. While alteplase is the global standard thrombolytic, Japan and several other Asian countries use a reduced dose of 0.6 mg/kg rather than the Western standard of 0.9 mg/kg — largely due to safety concerns about brain bleeding in Asian populations. Tenecteplase, a genetically engineered variant with higher fibrin specificity, longer half-life, and greater resistance to plasminogen-activator inhibitors, offers theoretical advantages but had never been compared directly to low-dose alteplase in a controlled trial until now.

The T-FLAVOR trial was an investigator-initiated, multicenter, open-label, superiority randomized controlled trial conducted across 22 Japanese stroke centers from August 2022 through March 2025. Patients with LVO stroke eligible for IV thrombolysis within 4.5 hours of symptom onset and planned for thrombectomy were randomized 1:1 to receive either IV tenecteplase 0.25 mg/kg (bolus) or IV alteplase 0.6 mg/kg (10% bolus, 90% infusion over 60 minutes). Of 221 randomized patients, 218 received trial drugs and constituted the full analysis set: 107 in the tenecteplase group and 111 in the alteplase group. Mean age was 77.1 years (SD 12.0), and 42% were female.

The primary endpoint — substantial reperfusion (mTICI 2b-3 or no retrievable thrombus on initial angiography) — was achieved in 11 of 107 tenecteplase patients (10.3%) versus 4 of 111 alteplase patients (3.6%). This absolute difference of 6.5 percentage points (90% CI, 0.89–12.1) met the prespecified success criterion. This result is clinically meaningful because early reperfusion before thrombectomy is associated with significantly better neurological outcomes and reduced procedural complexity, as the interventionalist may find no clot to retrieve.

Secondary outcomes showed a trend favoring tenecteplase. The common odds ratio for a shift toward better 90-day modified Rankin Scale (mRS) scores was 1.47 (95% CI, 0.92–2.35), suggesting roughly 47% higher odds of improved functional outcome with tenecteplase, though this did not achieve statistical significance. The proportion achieving mRS 0–2 (functional independence) at 90 days was numerically higher in the tenecteplase arm, consistent with the observed reperfusion advantage.

Safety outcomes were reassuringly similar. Symptomatic intracranial hemorrhage (sICH) within 24–36 hours occurred in 2.8% of tenecteplase patients versus 1.8% of alteplase patients — a non-significant difference. Ninety-day mortality was 6.5% with tenecteplase versus 9.9% with alteplase, again non-significant. These data suggest tenecteplase at 0.25 mg/kg does not carry an increased hemorrhagic risk compared to low-dose alteplase, an important finding for regulatory consideration in Japan, where the trial was designed in part to generate approval-supporting evidence.

The trial has several limitations. It was open-label due to drug formulation differences, introducing potential assessment bias, though the primary outcome was an objective imaging measure. The sample size was modest at 218 patients, and the trial was not powered for functional outcomes as a primary endpoint. Additionally, direct comparison with Western-standard alteplase (0.9 mg/kg) was not made. Nonetheless, the T-FLAVOR trial provides the first rigorous RCT evidence that tenecteplase 0.25 mg/kg meaningfully outperforms low-dose alteplase 0.6 mg/kg for pre-thrombectomy recanalization, with an acceptable safety profile — positioning tenecteplase as a compelling upgrade for LVO stroke care across Asia.