* 5 patients died in trials
* Analysts flag concerns about drug's future
* Shares tank in early trade (Recasts; adds analyst quote, updates shares)
Nov 15 (Reuters) - Acorda Therapeutics Inc said on Wednesday five people died in its Parkinson's disease drug trials, and it would stop enrolling new patients in two long-term safety studies, sending its shares down 34 percent in early trade.
The company, testing tozadenant, said in the mid-and late-stage trials it found seven cases of sepsis, with four associated with agranulocytosis - the absence of white blood cells.
Acorda said it would increase the monitoring of blood cell counts in patients in an ongoing related late-stage trial of tozadenant weekly, instead of every two weeks, monthly and once in a three-month assessment.
Tozadenant belongs to a new class of drugs called A2a receptor antagonists that can help improve motor symptoms in patients with Parkinson's disease.
"Investors will hold a more distressed view of the drug's odds of success and commercial potential as a byproduct of the update today," Leerink Research analyst Paul Matteis said.
The company has been hoping for the studies to succeed, particularly after a judge in March struck down key patents of its flagship multiple sclerosis drug Ampyra, which accounts for almost all of its revenue.
Following the verdict, investors mounted pressure on the company to sell itself.
Acorda acquired tozadenant last year when it took over Biotie Therapies Corp for $363 million.
Raymond James analysts said the news of fatal sepsis cases in the studies was unexpected, adding that with generic competition to Ampyra looming, a pipeline setback at this juncture raises concerns.
The company said it continues to expect to report data from the late-stage trial in the first quarter of 2018, after further talks with the Data Safety Monitoring Board and the U.S. health regulator.
Shares of the Ardsley, New York-based company plunged 34 percent to $18.60 in early trading. (Reporting by Divya Grover in Bengaluru; Editing by Bernard Orr and Saumyadeb Chakrabarty)