NEW YORK (TheStreet) -- Shares of Portola Pharmaceuticals (PTLA) - Get Report are diving by 28.83% to $20.37 on heavy trading volume Thursday afternoon, after the biopharmaceutical company released disappointing results from a phase 3 trial.

The South San Francisco-based company said its oral treatment for blood clots was not statistically different than the current standard of care.

The trial evaluated two anti-coagulation medications for the prevention of venous thromboembolism, or blood clots, in 7,513 patients. The acute medically ill patients in the study are defined as those hospitalized for serious common medical conditions, such as heart failure, stroke, infection and pulmonary disease.

There was no statistical difference in major bleeding between Portola's drug betrixaban and those given the standard of care injectable enoxaparin in the study, Portola said.

However, the company did observe positive net clinical benefit with betrixaban.

The number of intracranial hemorrhages, or bleeding that occurs inside the skull, was lower in the betrixaban arm of the trial, the company noted.

The results "will be subject to discussions with regulatory agencies," CEO Bill Lis said in a statement.

"We believe the overall robustness of the efficacy and safety results in this high-risk patient population, including the positive net clinical benefit observed, provide ample evidence to support the submission of an NDA later this year," he added.

About 13.39 million of the company's shares we traded by this afternoon, much higher than its average volume of 831,967 shares per day.

Separately, TheStreet Ratings Team has a "Sell" rating with a score of D on the stock.

This is driven by a few notable weaknesses, which should have a greater impact than any strengths, and could make it more difficult for investors to achieve positive results compared to most of the stocks covered.

The company's weaknesses can be seen in multiple areas, such as its feeble growth in its earnings per share, deteriorating net income, disappointing return on equity, weak operating cash flow and generally disappointing historical performance in the stock itself.

Recently, TheStreet Ratings objectively rated this stock according to its "risk-adjusted" total return prospect over a 12-month investment horizon. Not based on the news in any given day, the rating may differ from Jim Cramer's view or that of this articles's author.

You can view the full analysis from the report here: PTLA

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