(Reuters) - Drug developer Zogenix Inc said on Tuesday that it would push back late-stage trials of its treatment for a rare form of epilepsy by about three months to enroll more patients.

The company said it now planned to begin late-stage trials of the drug, ZX008, in the fourth quarter, and would seek to enroll 105 patients in the studies, up from 40 to 60 earlier, acting on guidance from the U.S. Food and Drug Administration.

The drug is aimed at treating children with Dravet syndrome, a rare form of epilepsy that begins in infancy. Patients suffer from potentially fatal, long-lasting, fever-related seizures that do not respond to standard medication.

Investors held to the stock after the company's decision to expand and delay the study.

Zogenix's shares, which have gained 44 percent so far this year, were up 4 percent in morning trading after touching a year-high of $16.60 earlier.

Stifel Nicolaus analyst Annabel Samimy said the slip in timing was not "dramatically different", and that she expected the company's investigational new drug (IND) application to be approved within 30-60 days.

Zogenix acquired ZX008 when it bought U.K.-based private company Brabant Pharma in October 2014. The treatment currently has orphan drug status in the United States and Europe.

(Reporting by Anjali Rao Koppala in Bengaluru; Editing by Savio D'Souza and Simon Jennings)