Feb. 22 (Bloomberg) -- Daiichi Sankyo Co., Japan's third- largest drugmaker, climbed the most in three months in Tokyo trading after U.S. regulators promised a priority review of a clot-blocker being developed with Eli Lilly & Co.

The Food and Drug Administration may complete prasugrel's appraisal in June, giving doctors a new medicine for preventing blood clots in people undergoing artery-clearing treatment, the companies said in a statement. Daiichi jumped 4.2 percent as the Tokyo-based company moved closer to its first U.S. release of an original drug since the Benicar blood-pressure pill in 2002.

The FDA cleared only 19 drugs in 2007, the fewest in 24 years, and an expedited review suggests the agency recognizes prasugrel's advantages. The tablet prevented more heart attacks and strokes than Plavix, an $8.1 billion seller in 2007 for Bristol-Myers Squibb Co. and Sanofi-Aventis SA, though heightened the risk of bleeding, a patient study showed.

``We can judge that prasugrel was deemed to be needed by those on the frontlines of medicine,'' said Yasuhiro Nakazawa, a pharmaceuticals analyst at Mitsubishi UFJ Securities Co., in a note to clients today. ``This is positive news for Daiichi.''

Daiichi climbed 130 yen to 3,200 yen on the Tokyo Stock Exchange, the biggest gain since Nov. 5, adding to yesterday's 4.1 percent increase. The advance made Daiichi one of the biggest gainers by index points on the MSCI Asia Pacific Index.

Ube Industries

Daiichi and its Japanese research partner, Ube Industries Ltd., discovered prasugrel as a potential treatment, initially for patients undergoing angioplasty for chest pain related to decreased blood flow to the heart.

Ube, based in Yamaguchi prefecture in western Japan, surged 21 yen, or 7.2 percent, to 311 yen after adding 4.3 percent yesterday.

``The fact that approval for the drug may come on June 26, instead of Dec. 26, is extremely good news,'' said Kenji Masuzoe, a health-care analyst at Deutsche Securities Inc. in Tokyo. ``There are many patients for whom Plavix isn't effective. The potency of prasugrel was probably taken into account'' in the FDA's assessment, he said in an interview today.

Demand for blood thinners has surged as a way to prevent cardiovascular disease, particularly in patients undergoing angioplasty. Prasugrel, whose proposed trade name is Effient, works by preventing platelets in the blood from clumping and causing clots that can lead to heart attacks and death.

Some clotting is essential to healing because it stops bleeding after surgery and injuries. In patients who weigh less than 60 kilograms (132 pounds), are older than 75, or who have previously had a stroke, prasugrel is likelier than Plavix to cause fatal bleeding.

Lower Stroke Risk

Prasugrel lowered the risk of heart attack, stroke and other cardiovascular conditions by 19 percent in patients with acute coronary syndrome undergoing artery-clearing procedures, Lilly and Daiichi Sankyo said in November, citing a patient study.

Doctors at the American Heart Association's meeting in November, where the data were shown, disagreed whether the FDA will require more data.

The mixed results also caused analysts to back away from estimates that prasugrel could generate as much as $4 billion a year. The drug may bring in $75 million in 2008, $375 million in 2009 and $900 million in 2011, Summer Street Research Partners said in November in a note to clients.

Investors will be watching for the results of late-stage patient studies on prasugrel, to be released at a medical meeting next month, said Hirohisa Shimura, an analyst at UBS Securities Japan Ltd. ``Demand among patients for whom Plavix isn't effective is high,'' he said.

Blockbuster Potential

Deutsche Securities' Masuzoe isn't ready to change his annual sales estimate of as much as $1 billion dollars for prasugrel until he learns the terms under which the drug is approved, he said.

``When the FDA decides on a priority review, it's usually the case that results of phase-three trials have been revealed in advance,'' said Ryoichi Urushihara, a health-care analyst at Nomura Holdings Inc. in Tokyo. ``I can't recall a priority review being granted like this. This is a positive surprise.''

Cardiovascular disease kills 16.7 million people each year, and acute heart attacks and unstable angina, called acute coronary syndrome, affect more than 800,000 people in Europe each year, Lilly and Daiichi said in a Feb. 20 statement.

The companies asked the European Medicines Agency to approve prasugrel for sale in the European Union earlier this month. If approved by regulators, Daiichi Sankyo will market the drug in the domestic market and with Lilly elsewhere. Sales will be booked by Lilly, from which Daiichi Sankyo will receive revenue.

Lilly shares rose $1.43, or 2.9 percent, to $51.25 at 5:43 p.m. in trading after the close of the New York Stock Exchange yesterday.

To contact the reporters on this story: Hideki Sagiike in Tokyo at at hsagiike@bloomberg.net; Elizabeth Lopatto in New York at elopatto@bloomberg.net.

Last Updated: February 22, 2008 01:39 EST