(Reuters) - Zogenix Inc’s experimental treatment for a rare form of epilepsy met the main goal in a late-stage study, the company said on Friday, more than doubling the value of its shares and hurting those of peer GW Pharmaceuticals .

In the trial, Zogenix’s drug was superior to a placebo in reducing the number of seizures in children with Dravet syndrome, a genetic dysfunction in the brain.

The disorder causes potentially fatal, long-lasting, fever-related seizures that do not yet have a standard treatment.

Zogenix shares surged almost threefold in premarket trading before settling at $28.65, up from Thursday’s close of $12.87.

The results also knocked as much as 14 percent off shares in British drugmaker GW, which is expected to file an application next month with U.S. regulators to market its own Dravet treatment - Epidiolex.

Treatment options for Dravet sufferers are currently limited, involving a combination of drugs for the seizures and to prevent emergencies. Analysts said that increased the chances of both treatments becoming standard therapy.

“Nearly every Dravet patient is treated with several anti-epileptics simultaneously,” Cowen and Co analyst analyst Phil Nadeau said in a report to clients.

Zogenix’s drug, ZX008, also reduced the number of patients suffering seizures when compared with a placebo, the results showed.

The California-based company said it expected to report data from a second late-stage trial in the first half of next year and remained on track to submit regulatory approvals for the drug in the United States and Europe in the second half of 2018.

It also plans to initiate a late-stage trial to test ZX008 in patients with Lennox Gastaut syndrome, another type of epilepsy affecting children, before year-end, Chief Executive Stephen Farr said on a call with analysts.

Zogenix acquired ZX008, its lead and only drug, in 2014 after buying Brabant Pharma.