NEW YORK (TheStreet) -- Tekmira Pharmaceuticals  (TKMR) plunged Thursday after the company announced it had received verbal notice from the FDA of a clinical hold on the company's TKM-Ebola Phase I clinical trial.

"We have completed the single ascending dose portion of this study in healthy volunteers without the use of steroid pre-medication," Tekmira said in a statement. "The FDA has requested additional data related to the mechanism of cytokine release, observed at higher doses, which we believe is well understood, and a protocol modification designed to ensure the safety of healthy volunteer subjects, before we proceed with the multiple ascending dose portion of our TKM-Ebola Phase I trial.

"We will continue our dialogue with the FDA, provided for under our Fast Track status, in order to advance the development of this important therapeutic agent."

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The stock was down 15.68% to $11.61 at 11:56 a.m. More than 1.1 million shares had changed hands by that point, compared to the average volume of 441,864.

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