UPDATE 1-FDA refuses to review Alkermes' depression treatment, seeks more trials

trials@ (Adds details about FDA's request, background on Alkermes' drug)

April 2 (Reuters) - Alkermes Plc's application for approval of an experimental depression drug has been rejected by the U.S. Food and Drug Administration due to a lack of evidence of its effectiveness.

The FDA said it was recommending additional clinical trials for the drug.

Shares of the company were down 17.2 percent to $48 in trading before the bell.

The company said it strongly disagreed with the FDA and planned to appeal the regulator's decision after the regulator sent a "Refusal to File" letter to the company.

The FDA was unable to complete a review of the marketing application, the company said. The FDA has also requested a bioavailability study to show bridging data between the drug and the reference drug, buprenorphine.

ALKS 5461, a once-daily pill combining samidorphan and buprenorphine, is designed to rebalance brain function that becomes dysregulated in the state of depression.

In Oct 2016, ALKS 5461 significantly reduced symptoms of depression compared to a placebo in a third late-stage study, after failing to achieve efficacy goals in two earlier late-stage studies.

An estimated 16.2 million people in the United States suffered from major depressive disorder in 2016, according to the company, and a majority of the patients do not adequately respond to initial anti-depressant therapy. (Reporting by Manas Mishra in Bengaluru; Editing by Shailesh Kuber)