(Reuters) – Acasti Pharma Inc said on Monday its krill oil-derived drug had failed to beat placebo by a large margin in reducing a type of fat found in blood that increases the risk of heart diseases, sending its shares spiraling down nearly 67%.

The company said the drug, CaPre, derived from shrimp-like crustaceans called krill, showed a 36.7% median reduction in triglyceride levels after 26 weeks of treatment, compared with an average of 28% reduction among those on placebo.

Though the difference at 26 weeks was in favor of CaPre, due to an unexpectedly large positive placebo response, CaPre’s response did not meet statistical significance in the late-stage study, Acasti said.

The larger-than-expected declines in triglyceride levels in the placebo group remain unexplained and highly unusual, the study’s main investigator Dariush Mozaffarian said.

A high placebo response at 5 enrolling sites out of a total of 54, disproportionately contributed to the overall placebo response and is being further investigated, Acasti said.

An outcome from the investigation is expected by the end of February.

CaPre, like Amarin Corp Plc’s fish-oil derived therapy Vascepa and GlaxoSmithKline Plc’s heart pill Lovaza, contains omega-3 fatty acids – substances found in foods and dietary supplements such as fish oil.

Capre is a combination of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) – two omega-3 fatty acids found in fish and other seafood.

Amarin’s Vascepa, which is purified EPA only, won U.S. approval to lower high triglycerides in 2012 and for its expanded use in reducing the risk of heart attacks and strokes in high-risk patients last month.

Acasti is also testing CaPre in another late-stage study, results from which are now expected to be delayed to mid-February. The study’s results may provide more insight into the placebo response seen in the latest trial, the company said.

The company’s U.S.-listed shares were down at 72 cents before the opening bell, while those of Amarin were up about 6% at $20.07.

(Reporting by Manojna Maddipatla and Trisha Roy in Bengaluru; Editing by Maju Samuel and Shinjini Ganguli)