* Bayer plans two new Phase III trials, one Phase II
* Trials could add to Xarelto's 5 approved indications
* Bayer won't say whether it may raise peak sales estimate (Adds senior manager quotes, further details of trials)
FRANKFURT, Aug 29 (Reuters) - Germany's Bayer unveiled plans to launch three new studies to expand the uses of its anti-clotting drug Xarelto, one of its top five new medicines.
Xarelto, which competes with the Eliquis pill developed by Bristol-Myers Squibb and Pfizer in stroke prevention, reached sales of $1.7 billion in the 12 months to June. Analysts estimate annual sales could rise to more than $9.5 billion by 2020.
The drug, jointly developed with U.S. firm Johnson & Johnson , is currently approved for uses including the prevention of strokes caused by atrial fibrillation, a type of arrhythmia.
Bayer said on Friday that a Phase III trial involving about 7,000 patients would examine whether Xarelto can help prevent the recurrence of strokes in patients who have suffered strokes of undetermined cause.
"We really have just as many strokes due to undetermined causes as to atrial fibrillation," Frank Misselwitz, head of the Therapeutic Area Cardiovascular and Coagulation at Bayer HealthCare, told Reuters.
A second Phase III trial announced on Friday will examine the potential benefits of Xarelto in reducing thrombotic vascular complications in more than 5,000 patients with peripheral artery disease.
The third new study is a Phase II trial designed to evaluate Xarelto for long-term prevention of acute coronary syndrome in patients who have suffered from the illness. If the study involving between 2,000 and 3,000 patients is successful, a Phase III study will follow, Bayer said.
Misselwitz declined to say whether expanding the uses of Xarelto would prompt Bayer to raise its estimate of the drug's peak sales potential, which Chief Executive Marijn Dekkers has so far put at about 3.5 billion euros a year.
"But these are major illnesses," Misselwitz said with reference to the planned trials.
Bayer shares were flat at 1441 GMT, against a 0.8 percent lower Dax index.
Xarelto is also currently used to treat and prevent deep vein thrombosis and pulmonary embolisms and to reduce the risk of strokes and blood clots in patients with an irregular heart beat that is not caused by heart problems.
($1 = 0.7592 euro) (Reporting by Frank Siebelt; Writing by Maria Sheahan; Editing by Jonathan Gould and Pravin Char)