January 04, 2012, 10:17 AM EST

By Sarah Frier

(Updates with share price in the sixth paragraph.)

Jan. 4 (Bloomberg) — Alkermes Plc, the maker of central nervous system drugs, said it will move faster than scheduled to test an experimental treatment for depression after a successful early-stage trial.

Alkermes, based in Dublin, is seeking a market of people who don’t respond to typical depression medicines such as Eli Lilly & Co.’s Prozac, Chief Executive Officer Richard Pops said. About half of people don’t respond to their first therapy, the CEO said.

The experimental drug, ALKS 5461, targets opioid receptors in the brain. It combines buphrenorphine, which stimulates the receptors and is used to treat heroin addiction, with ALKS 33, which has the opposite effect, making a non-addictive medicine that may treat depression, Pops said in a telephone interview.

“We’re very interested in those cases where drugs have been developed before and we think we can fill a patient need,” Pops said.

The compound was tested in a study of 32 patients for seven days and recorded a reduction in depression symptoms, as measured by the Hamilton Depression Rating Scale, the company said in a statement. The results, released today, have led Alkermes to start the treatment in the second of three phases of clinical trials usually needed for U.S. regulatory approval. The company also is developing ALKS 5461 for cocaine addiction.

Alkermes slipped less than 1 percent to $17.32 at 9:47 a.m. in New York. The stock gained 41 percent in 2011.

–Editors: Andrew Pollack, Angela Zimm

To contact the reporter on this story: Sarah Frier in New York at sfrier1@bloomberg.net;

To contact the editor responsible for this story: Reg Gale at rgale5@bloomberg.net