* 5 patients dead in trials
* Analysts flag concerns about drug's future
* Shares slump 40 pct premarket (Adds details on deaths, analyst comment; updates shares)
Nov 15 (Reuters) - Acorda Therapeutics Inc said it halted enrolling patients in two late-stage safety studies of its Parkinson's disease drug following deaths, sending its shares tumbling more than 40 percent in premarket trading.
The company said five people died in mid- and late-stage trials following 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 the drug, tozadenant, every week.
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.
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 40.4 percent to $16.80 in premarket trading on Wednesday. (Reporting by Divya Grover in Bengaluru; Editing by Maju Samuel and Saumyadeb Chakrabarty)