(Corrects designation of drug in paragraph 8 to SAGE-547 from SAGE-547c)
By Natalie Grover
May 14 (Reuters) - A drug being developed by Sage Therapeutics Inc is set to enter a late-stage study, putting it a step closer to becoming the first specific therapy for a life-threatening seizure disorder.
Sage said on Thursday that a tiny mid-stage study of its lead drug evoked a 77 percent response rate in patients with super-refractory status epileptics (SRSE).
Status epileptics (SE) is condition in which the brain is in a persistent state of seizure. It afflicts about 150,000 people in the United States.
A patient who does not respond to the usual anti-seizure drugs must be placed in a chemically induced coma.
The patient is diagnosed with SRSE - a condition considered almost incompatible with a conscious existence - if the seizure persists after awakening. The patient is then put back to sleep.
"It's almost like an artificial hibernation to keep the brain and the body at rest in the hopes that something can be done for the patient," Sage Chief Executive Jeff Jonas said in an interview.
Two-thirds of the 25,000 people with SRSE in the United States each year end up either disabled or dead.
Sage first tested its intravenous drug, SAGE-547, in a patient in March 2014 and plans to start a late-stage study in the middle of this year.
Jonas said that if all goes well, the drug could be commercially available by 2018.
The drug has been granted both fast-track and orphan drug status by the U.S. Food and Drug Administration to treat SRSE.
It is also being evaluated to treat postpartum depression and essential tremor.
In trial data published on Thursday, Sage said six patient deaths occurred during the study period, all resulting from the underlying medical condition.
Shares of Cambridge, Massachusetts-based Sage, which has two other drugs in its pipeline, have risen more than three times since the company public in July 2014.
Up to Wednesday's close of $57.29, the stock had risen 57 percent since the start of the year.
Reporting by Natalie Grover in Bengaluru; Editing by Ted Kerr