Purified Snake Venom for Treatment of Stroke
Clinical Reviews
With Comments from Lynn Keegan, RN, PhD, HNC, FAAN
Purified Snake Venom for Treatment of Stroke
Source: Sherman DG, et al. Intravenous ancrod for treatment of acute ischemic stroke. JAMA 2000:283:2395-2403.
Context: Approved treatment options for acute ischemic stroke in the United States and Canada are limited at present to intravenous tissue-type plasminogen activator, but bleeding complications, including intracranial hemorrhage, are a recognized complication. An evaluation of other options is needed.
Objective: To evaluate the efficacy and safety of the defibrinogenating agent ancrod (purified snake venom) in patients with acute ischemic stroke.
Design: The Stroke Treatment with Ancrod Trial (STAT), a randomized, parallel-group, double-blind, placebo-controlled trial conducted between August 1993 and January 1998.
Setting: Forty-eight centers, primarily community hospitals, in the United States and Canada.
Patients: Five hundred patients with acute or progressing ischemic neurological deficit were enrolled and included in the intent-to-treat analysis.
Interventions: Patients were randomly assigned to receive ancrod (n = 248) or placebo (n = 252) as a continuous 72-hour intravenous infusion beginning within three hours of stroke onset, followed by infusions lasting approximately one hour at 96 and 120 hours. The ancrod regimen was designed to decrease plasma fibrinogen levels to 1.18-2.03 mmol/L.
Main Outcome Measures: The primary efficacy end point was functional status. Favorable functional status defined as survival to day 90 with a Barthel Index of 95 or more or a Barthel Index score of at least the prestroke value, compared by treatment group. Primary safety variables included symptomatic intracranial hemorrhage and mortality.
Results: Favorable functional status was achieved by more patients in the ancrod group (42.2%) than in the placebo group (34.4%; P = 0.04) by the prespecified covariate adjusted analysis. Mortality was not different between treatment groups (at 90 days, 25.4% for the ancrod group and 23% for the placebo group; P = 0.62), and the proportion of severely disabled patients was less in the ancrod group than in the placebo group (11.8% vs. 19.8%; P = 0.0l). The favorable functional status observed with ancrod vs. placebo was consistent in all subgroups defined for age, stroke severity, sex, prestroke disability, and time to treatment (roughly three hours after stroke onset). There was a trend toward more symptomatic intracranial hemorrhages in the ancrod group vs. placebo (5.2% vs. 2.0%; P = 0.06), as well as a significant increase in asymptomatic intracranial hemorrhages (19.0% vs. 10.7%; P = 0.0l).
Conclusion: In this study, ancrod had a favorable benefit-risk profile for patients with acute ischemic stroke. Therapeutic benefits and a favorable safety profile of ancrod appear to be related to achieving controlled defibrinogenation.
Comment: Ancrod is a purified fraction of venom from the Malaysian pit viper. Its therapeutic value lies in its ability to induce rapid defibrinogenation in humans by splitting fibrinopeptide. Ancrod has been used in Europe and Canada since the 1970s as reperfusion therapy for clinical conditions such as peripheral vascular disease, deep vein thrombosis, and central retinal venous thrombosis. This product is an example of what therapeutic agents may be found in tropical rain forests and gives support to activists who lobby on behalf of saving and restoring the environment. Nurses will want to add this information to their arsenal of facts on new methods to combat the age-old problem of acute cerebrovascular accident. The development of a medication derived from snake venom is another example of how alternative approaches can blend with conventional thinking to produce a new product.
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