Tonix Pharmaceuticals Holding Corp said a higher dose of its experimental drug for post-traumatic stress disorder (PTSD) helped control symptoms in patients, sending its shares surging 46 percent in premarket trading.

A 5.6 mg dose of the drug, TNX-102 SL, showed promise, but the lower 2.8 mg dose did not have a statistically significant effect, Tonix said on Thursday.

The 5.8 mg arm was designed to include half the number of patients in the 2.8 mg arm, the company said.

Tonix said it would take the 5.6 mg dose into late-stage trials after discussions with the U.S. Food and Drug Administration.

If approved, the drug would be the first to hit the market to treat the psychiatric disorder in more than 15 years.

PTSD affects about 8.4 million Americans and is a severely debilitating condition in which patients re-experience horrific traumas from the past in forms of intrusive memories, flashbacks and nightmares.

The trial tested the treatment in military personnel, a population in which PTSD is more prevalent.

Up to 20 percent of Operation Enduring Freedom and Operation Iraqi Freedom veterans, up to 10 percent of Gulf War veterans and up to 30 percent of Vietnam War veterans are estimated to have experienced PTSD, according to the U.S. Department of Veteran Affairs.

Tonix's shares pared some of their gains and were up 29 percent at $3.74 in premarket trading.

(Reporting by Amrutha Penumudi in Bengaluru; Editing by Sriraj Kalluvila)