April 1 (Reuters) - Axsome Therapeutics ( AXSM ) said on

Tuesday it will narrow the focus of a late-stage study of its

depression drug after an initial run of the trial showed

improvement only in a small subgroup of patients.

The drug, solriamfetol, did not show statistically

significant improvement in the overall group of patients.

However, it helped reduce symptoms in some patients with

major depressive disorder who also suffered from excessive

daytime sleepiness (EDS), a common symptom of MDD.

"The study missing in the overall MDD population limits the

market opportunity significantly, and is disappointing given the

company's expertise in the space," RBC Capital Markets analyst

Leonid Timashev said in a client note.

Axsome said it plans to start a larger late-stage study of

the drug in MDD patients with EDS this year.

The initial late-stage study that served as a proof of

concept for the larger trial had enrolled 346 participants with

MDD, of which 51 patients had severe EDS, the company said.

The drug was well-tolerated in the study with no new safety

concerns, Axsome said.

Each year, around 21 million adults in the U.S. are affected

by MDD, according to the company.

Solriamfetol has already been approved in the U.S. to

improve wakefulness in adults with excessive sleepiness from

sleep disorders, narcolepsy and sleep apnea, and is sold under

the brand Sunosi.