NEW YORK (TheStreet) -- Shares of Seres Therapeutics (MCRB) - Get Reportare plummeting 68.82% to $11.15 this afternoon on heavy trading volume after the company's experimental recurrent Clostridium difficile infection drug, SER-109, failed to meet its primary endpoint in a clinical trial.

Over 17.75 million shares of the Cambridge, MA-based microbiome therapeutics company have traded so far today, well above its average of 301,000 per day.

In the drug's phase two trial, patients who were administered the treatment had lower rates of C. diff infection recurrence but the results were not statistically significant.

An earlier trial of the drug had shown strong results, which led the FDA to give SER-109 a breakthrough therapy designation.

"These are unexpected clinical results in view of the positive data in our prior investigator-sponsored Phase 1b trial," CEO Roger Pomerantz said in a company statement.

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