Pharmaceuticals maker AstraZeneca ( AZN) is beginning two major Phase III clinical trials to determine the effect of Cerovive on acute ischemic stroke patients. The clinical trial program will compare the effectiveness and safety of a 72-hour intravenous infusion of the drug given within six hours of the onset of symptoms vs. a placebo. Two studies will be enrolling more than 3,000 patients. One trial will involve 200 centers across 24 countries in Europe, Asia, Australia and South Africa. Another study will have patients from about 150 sites in the U.S., Canada and South America. Acute stroke is the third leading cause of death in North America and Western Europe and the most common cause of adult disability. Every year about 1.8 million new cases will occur in the major industrialized countries, AstraZeneca said. Cerovive has been licensed from Renovis of South San Francisco, Calif. Renovis said it has received two milestone payments from AstraZeneca in connection with the clinical trials. Under the agreement, Renovis will receive additional milestone payments based on the successful development of Cerovive and royalties on worldwide sales of the drug. Phase I/II trials, including two trials in acute stroke patients, have been completed to determine the appropriate dose and tolerability of Cerovive. Shares of AstraZeneca were down 15 cents to $40.70 in early New York Stock Exchange trading.