TNK Dose in Large-Vessel Stroke: 0.25 mg/kg Is Sufficient

February 20, 2020

A new study suggests that the 0.25-mg/kg dose of the thrombolytic tenecteplase (TNK) is just as good at facilitating reperfusion of the blocked artery in patients with ischemic large-vessel stroke prior to planned thrombectomy as the higher 0.4-mg/kg dose.

The EXTEND-IA TNK Part 2 trial was presented today at the American Stroke Association's International Stroke Conference (ISC) 2020 in Los Angeles, California, and was simultaneously published online in JAMA.

"We found the 0.4-mg/kg dose was no better than 0.25 mg/kg. There was absolutely no perceptible difference, so it appears that 0.25 mg/kg is enough," lead investigator Bruce Campbell, MBBS, PhD, told Medscape Medical News.

"Our study was conducted in patients with large-vessel occlusions heading for thrombectomy, but I think the results can be extrapolated to patients with smaller occlusions too," he added.

The study also showed that one fifth of patients given tenecteplase experienced reperfusion before thrombectomy was performed. The percentage rose to one third among patients from rural areas, whose longer times in transport led to an increase in the time between thrombolysis and thrombectomy.

"I think these data are as good as we're going to get on the optimal dose of TNK. Our endpoint was reperfusion rates ― a good, solid biological marker of benefit ― but if a difference in clinical outcomes is wanted, that would take a trial of several thousand patients, which is never likely to be done," said Campbell, who is from the Department of Neurology at the Royal Melbourne Hospital, Australia.

The researchers note that tenecteplase has a practical advantage over alteplase in that it is given as a bolus injection, whereas alteplase is given as bolus followed by a 1-hour infusion.

Results from the first EXTEND-IA TNK study suggested that tenecteplase 0.25 mg/kg produced higher reperfusion rates than alteplase. However, the larger NOR-TEST study found no difference in efficacy or safety between a 0.4-mg/kg dose of tenecteplase and alteplase in patients with mild stroke.

TNK use in stroke varies around the world. The drug is not licensed for use in stroke anywhere, which Campbell attributes to a lack of incentive for the manufacturer, Genentech/Boehringer Ingelheim. That company also markets alteplase, the main thrombolytic used in stroke.

But many countries have now included TNK in their stroke guidelines, Campbell noted. "This has only recently occurred in the US, where it has a 2b recommendation, and the dose recommendations are somewhat confusing, advocating 0.25 mg/kg in large-vessel occlusions (as was used in the first EXTEND IA study) and 0.4 mg/kg in non-large-vessel occlusions (from the NOR-TEST trial).

"This makes no biological sense whatsoever, recommending a higher dose for smaller occlusions, but that is just a literal translation of the design of the two major studies. I'm hoping our current results will help clarify the dosage issue and that might encourage more use of TNK altogether," he commented.

For the current study, conducted in Australia and New Zealand, 300 patients who had experienced ischemic large-vessel stroke within 4.5 hours of symptom onset and who were scheduled for endovascular thrombectomy were randomly assigned to receive open-label thrombolysis with tenecteplase 0.4 mg/kg or 0.25 mg/kg.

The primary outcome, reperfusion of greater than 50% of the involved ischemic territory prior to thrombectomy, occurred in 19.3% of both groups. There was also no difference in any of the functional-outcome secondary endpoints or all-cause mortality between the two doses.

"While we didn't find any extra benefit of the 0.4-mg/kg dose over the 0.25-mg/kg dose, we also didn't find any extra harm, and this gives us reassurance in the emergency situation if the weight of the patient is overestimated; then we have a window of safety," Campbell commented. "While there was a nonsignificant numerical increase in intracranial hemorrhage in the 0.4-mg/kg group, the excess bleeds were caused by puncturing of the vessels during thrombectomy, so I don't think we can blame the TNK dose for that."

Better Reperfusion Than With Alteplase?

Noting that the original EXTEND-IA TNK study showed higher reperfusion rates with tenecteplase vs alteplase and a trend toward better outcomes on the mRS scale, Campbell reported that a pooled analysis of the TNK results from the current study with those from the first study confirmed these findings.

"We found a doubling in the rate of reperfusion with TNK vs alteplase, and the mRS shift analysis remained positive," he said.

"I think we say with confidence that TNK is at least as good as alteplase and probably better, but further studies comparing the two agents are ongoing," he added.

Of note, for the 41 patients from rural areas in the current study, in whom the time from thrombolysis to thrombectomy was longer (152 min vs 41 min for patients from urban areas), reperfusion rates were higher (34% vs 17%), and there was no difference in dosage between the two groups.

Commenting on these latest results for Medscape Medical News, Nicola Logallo, MD, Haukeland University Hospital, Bergen, Norway, who was part of the NOR-TEST trial, said: "There is some evidence supporting the use of TNK 0.4 mg/kg in mild stroke patients, based mainly on the results from the NOR-TEST trial, and the use of TNK 0.25 mg/kg in patients undergoing thrombectomy, based on Campbell's previous EXTEND-TNK trial. Campbell's new study confirms that probably the higher dose of TNK does not add any advantages in terms of clinical outcome."

Hemorrhagic complications appear to be similar in the two groups, Logallo said. "Overall, the 0.25-mg/kg TNK dose could therefore be considered as the most convenient and sensible, at least in patients undergoing thrombectomy. When it comes to the remaining stroke patients receiving thrombolysis, it remains unclear which is the best dose, but studies such as TASTE, NOR-TEST 2, AcT, and ATTEST-2 will hopefully answer this question within the next years."

Also commenting on the study, Michael Hill, MD, professor of neurology at University of Calgary, Alberta, Canada, said the results "confirm that a good proportion of patients given TNK reperfuse before the angiogram and clarifies the dose. This is useful information."

Hill said TNK is used routinely in some countries ― mainly in Australia and Norway, where the studies have been conducted ― but there is now a movement toward use of TNK in North America too.

"Studies so far suggest that it could be more effective than alteplase, and, as it is more fibrin specific, it could be safer. It is also easier to give with a bolus dose, but perhaps the biggest driver might be that it is cheaper than alteplase. Momentum is building, and many leading investigators are now conducting new studies with TNK with several more studies coming out in the next year or so," Hill added.

The EXTEND-IA TNK Part 2 trial was supported by grants from the National Health and Medical Research Council of Australia and the National Heart Foundation of Australia. Campbell reports receiving grants from both institutions during the conduct of the study.

International Stroke Conference (ISC) 2020: Abstract LB1. Presented February 20, 2020.

JAMA. Published online February 20, 2020. Full text

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