Window Of Opportunity

Once a drug dose is determined, the investigator must then determine the most effective time to administer the drug—the window of opportunity. In many studies, drugs are administered preischemia or at reperfusion; however, although these types of administration may be excellent from the viewpoint of elucidating mechanisms of neuroprotection, they may not have any therapeutic value to the patient with stroke or cardiac arrest ischemia. In the past, few studies have carefully evaluated administration of potential neuroprotective drugs at 5, 15, 30, or 60 min following reperfusion, and even fewer have examined drug administration times of 3, 6, 12, 24 hr, or longer, after the ischemic event. In preclinical animal models, it is precisely known when the ischemia occurs, for the investigators induce it as part of the protocol. Thus, it is easy to choose windows of opportunity for administering a drug; however, ischemia onset is not at all controlled in the clinical situation. Individuals who suffer an ischemic event often require considerable time to obtain treatment; calling the physician, calling 911, waiting for a response, transporting to a hospital, obtaining a brain scan, etc. may require hours, rather than minutes. Thus, to perform expensive clinical trials with proposed neuroprotective drugs administered at 3 hr after the event, when these drugs have never been shown to be efficacious at that time in animal models, seems extremely risky, would not be predictive of success, and might be considered inappropriate. It may well be that the reason clinical trials with NMDA antagonists and other drugs (24,25,37-39) were shown not to be effective in humans was due, in part, to the inability to treat within the window of opportunity demonstrated in animal models. For example, the NMDA antagonists are effective in animal models only in a narrow therapeutic window following ischemia. Another issue is that the best window of opportunity in animal models may be different than that in humans; nevertheless, studies must be performed in animals in order to make an educated guess about which window to use in humans.

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