NEW YORK (TheStreet) -- Shares of Alnylam Pharmaceuticals  (ALNY) were down 43.03% to $40.75 in after-hours trading on Wednesday after the biopharmaceutical company stopped development of its drug revusiran.

A late-stage study of the treatment determined that more patients died after receiving the drug than receiving a placebo, the Cambridge, MA-based company said in a statement. 

Revusiran was being developed to treat hereditary amyloidosis with cardiomyopathy, which can lead to nerve and heart damage.

"Patient safety comes first. We have stopped all dosing and are actively monitoring patients across revusiran studies to ensure their safety," CEO John Maraganore said in a statement.

The decision to end revusiran development does not impact the company's patisiran drug, which is in Phase III development for the treatment of hereditary ATTR amylydosis with polyneuropathy.

Separately, TheStreet Ratings team rates the stock as a "sell" with a ratings score of D.

Alnylam's weaknesses include its deteriorating net income, disappointing return on equity, weak operating cash flow, generally disappointing historical performance in the stock itself and feeble growth in its earnings per share.

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

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 article's author.