February 26, 2014

SAN DIEGO, California — If tissue plasminogen activator (tPA) can be shown to be effective in mild stroke in large-scale trials, it will provide good economic value to the healthcare system, a new cost-effectiveness analysis suggests.

The study was presented by David Veenstra, PhD, University of Washington, Seattle, at the International Stroke Conference (ISC) 2014.

Use of tPA is indicated for moderate to severe stroke. The current modeling analysis was based on limited data on its use in mild stroke from a subset of patients the third International Stroke Trial (IST-3).

"The big limitation of our study is that we don't have much effectiveness data yet in mild stroke, so we can't say with authority that it does work in this population, but a large randomized trial of tPA in mild stroke is now starting," Dr. Veenstra commented to Medscape Medical News.

The new study is called Potential of rtPA for Ischemic Strokes with Mild Symptoms (PRISMS). "This cost-effectiveness analysis was part of the justification for performing that study," he said.

The IST-3 results were published in The Lancet in 2012 and reported by Medscape Medical News at that time.

Dr. David Veenstra

Good Economic Value

Dr. Veenstra explained that tPA is of unusually good economic value in moderate to severe stroke because it is actually cost saving, being associated with a gain of 0.39 quality-adjusted life-years (QALYs) and a cost saving of $25,000 per patient.

But half of stroke patients present with mild stroke, and one third of untreated mild strokes result in significant disability, he reported.

"In IST-3 there were 106 patients (3.5%) with mild stroke. We used data from these patients and from some pilot phase 2 studies of tPA in mild stroke to calculate life expectancy, clinical events and quality of life."

To do this, the researchers modeled stroke severity health states based on modified Rankin scale (mRS) and Oxford handicap scale scores using Markov techniques. Healthcare costs, QALYs, and incremental cost-effectiveness were calculated, and 1-way and probabilistic sensitivity analyses were conducted to assess uncertainty.

Results showed that the researchers' "best guess" on cost-effectiveness was that tPA in mild stroke would be associated with an increase of 0.36 QALYs and would be cost saving by $20,000 per patient.

But because there is so much uncertainty based on limited effectiveness data, the clinical benefit could range from a decrease of 0.15 QALYs to an increase of 0.83 QALYs and the cost-effectiveness could range from a cost saving of $60,000 to a cost increase of $20,000.

"We believe use of tPA in mild stroke would very likely provide good economic value to the healthcare system, but of course we can't say for sure based on such limited effectiveness data. That is why we need to conduct the PRISMS trial — to get better effectiveness data," Dr. Veenstra concluded.

For the study, researchers used data from IST-3, some pilot phase 2 studies and the ASAP trial, a prospective cohort of 136 consecutive patients with mild deficits (National Institutes of Health Stroke Scale score of 5 or less) presenting within 24 hours of onset, of whom 40 (29%) had poor outcomes (mRS score, 2 to 6) at 90 days.

In the 106 patients in the IST-3 mild stroke subgroup, 60% of tPA recipients vs 51% of the control group were alive and independent (mRS score, 0 to 1). This 9–percentage point absolute difference in nondisabled patients observed in the IST-3 subset was applied to the ASAP observational group to derive the tPA group for the cost-effectiveness analysis. The researchers assumed no mortality difference between treatment groups.

This gave a result of 0.79% of tPA recipients having an mRS score of 0 to 1 compared with 70% of untreated patients.

Acute costs were worked out as $8263 for patients with mRS scores of 0 to 1 vs $12,550 for patients with mRS scores of 2 to 5. Annual healthcare costs were calculated as $6214 for patients with mRS scores of 0 to 1 $33,132 for patients with mRS scores of 2 to 3, and $64,040 for patients with mRS scores of 4 to 5.

IST-3 was supported by Boehringer Ingelheim. Dr. Veenstra reports that he acts as a consultant to Genentech.

International Stroke Conference (ISC) 2014. Abstract 136. Presented February 13, 2014.

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