* FDA approves once-daily trazodone antidepressant

* Company seeking partnership for drug

* U.S. antidepressant market valued at $11 bln

* Shares up more than 15 pct in premarket trading (Adds company comments; in U.S. dollars unless noted)

TORONTO, Feb 3 (Reuters) - The U.S. Food and Drug Administration has approved a once-daily antidepressant made by Labopharm Inc , the Canadian company said, sending its shares up more than 15 percent in premarket trading.

The approval clears the way for the biotechnology company to launch the drug, trazodone, on the U.S. market later this year.

Labopharm President and Chief Executive James Howard-Tripp said the timing of the launch was contingent on the Montreal-based company finding a partner for the drug.

Howard-Tripp said Labopharm was studying several commercialization options for trazodone, including licensing the drug to another company or a co-promotion deal.

Although Howard-Tripp said Labopharm was in discussions with an "international" company concerning partnering, he refused to commit to a timeframe.

"We prefer to go down the co-promotion route where we will have more of a role (in the development)," he told Reuters. "This gives us a much higher degree of control of our own asset, and the financial return is significantly better."

Some 14 million adults in the United States suffer from major depression. The U.S. market for antidepressants is valued at more than $11 billion.

Howard-Tripp declined to set a yearly U.S. sales figure for the treatment, but TD Newcrest analyst Lennox Gibbs said in a recent report that if it fails to clear the $20 million threshold this year it would be an early indication that the launch was faltering.

Approval of the drug was stalled last year after the FDA raised concerns about the manufacturing process at an Italian plant that produced the drug's active ingredient.

Labopharm has also filed an application for approval with Canadian regulators and expects a decision sometime in August.

The U.S. approval of trazodone is the second approval for the company in less than a year. Last year it received approval for its tramadol-acetaminophen combination pain treatment. ($1=$1.06 Canadian) (Reporting by Scott Anderson; editing by John Wallace)