(Adds details on number of employees, share price)
June 13 (Reuters) - U.S. drug developer Flex Pharma Inc said on Wednesday it plans to stop two ongoing mid-stage trials, testing its lead drug to treat neuromuscular diseases, following safety concerns.
The company's shares fell 18.7 percent to $3.40 in premarket trading.
The drug, FLX-787, was being tested in trials to treat amyotrophic lateral sclerosis (ALS) and Charcot-Marie-Tooth disease, a rare neuromuscular disorder.
"Recent observations of oral intolerability ... indicate that more formulation and dose-ranging studies are required, which is challenging for the company based upon our current resources," Chief Executive Officer Bill McVicar said.
Based on the company's plans to stop the mid-stage trials, Flex would reduce its workforce by 60 percent. It had 20 full-time and two part-time employees as of March.
Flex now plans to shift the focus of its drug FLX-787 to treat dysphagia or difficulty in swallowing. (Reporting by Manas Mishra in Bengaluru; Editing by Shounak Dasgupta)