Alnylam Ends Development of Key RNAi Drug, Stock Drops

Alnylam Pharmaceuticals Inc. ended development of its late-stage experimental drug for a rare disease because of safety concerns, leading to a big drop in its stock price.

More patients taking the drug were dying compared to those getting a placebo, the company said in a statement after the market closed Oct. 5. The treatment, revusiran, was being tested for a condition called hereditary ATTR amyloidosis with cardiomyopathy, which can lead to nerve and heart damage.

“We’re very sad to report the outcome here,” Akshay Vaishnaw, Alnylam’s chief medical officer, said on a call with investors. “In terms of causality, we ...