UPDATE 1-ARYx shares tank after anticoagulant agent fails study

* Says anticoagulant agent fails trial

* Shares plunge as much as 54 pct (Adds analysts' comments; updates share movement)

By Vidya L Nathan

BANGALORE, July 8 (Reuters) - Shares of ARYx Therapeutics Inc ARYX.O lost as much as half their value Wednesday, a day after the drug maker said data from a clinical study of its anticoagulant agent failed to meet the main goal.

The company said its oral drug tecarfarin did not show statistically significant superiority to warfarin -- a widely used blood-thinning drug -- in a Phase II/III study.

While tecarfarin showed essentially the same efficacy as in earlier mid-stage studies, the company cited a higher-than-anticipated performance by warfarin for the failure of the trial.

"The (tecarfarin) program is clearly more risky now," Wedbush Morgan Securities analyst Duane Nash said.

"Now the question is: with the program having more risk will a partner still be willing to license the drug and fund a late-stage trial?"

While Nash believes the ARYx drug -- which he estimates has potential peak sales close to $1 billion -- would now take longer to partner, others think the company will not get as good a deal as it would have earlier.

"We still believe Tecarfarin is a partnerable, albeit with lower than previously expected terms," said Jefferies & Co analyst Marko Kozul, who cut his price target on the stock on the stock to $7 from $9.

The Fremont, California-based company said it would continue on-going partnership talks to decide on how to proceed with tecarfarin.

Shares of the company, which touched a low of $1.91 earlier in the session, were trading down 41 percent at $2.47 Wednesday afternoon, making them the top loser on Nasdaq. (Reporting by Vidya L Nathan in Bangalore; Editing by Anil D'Silva, Anthony Kurian)