Alnylam shares slide after heart drug data fails to impress investors

Aug 30 (Reuters) - Alnylam Pharmaceuticals' ALNY.O shares fell 11% before the bell on Friday, after data for its closely watched heart drug fell short of heightened investor expectations.

The company's shares have climbed more than 70% since it disclosed early results of the late-stage study of the drug, vutrisiran, in June.

Vutrisiran was tested in patients with transthyretin amyloid cardiomyopathy (ATTR-CM), where function of the heart muscles is restricted due to the accumulation of irregular proteins.

The drug helped reduce the of deaths and heart issue-related hospitalizations by 33% in the study, which enrolled 655 patients who either received the drug or a placebo, Alnylam had then said.

The detailed data showed that the drug, in combination with other treatments, reduced the risk of death through 36 months. It reduced the risk of death by 30% when tested alone, but this was statistically significant, the company said.

The detailed results of the study, released on Friday, were being watched by investors to see if the drug could perform as well as its rival treatments.

The data was "supportive of a strong commercial opportunity", analysts at BMO Capital Markets said, adding that they expect some volatility given the recent upside in Alnylam shares since the first readout.

Current treatment options for ATTR-CM include Pfizer's PFE.N tafamidis, sold as Vyndaqel and Vyndamax, which works by stabilizing production of the protein transthyretin.

Alnylam shares fell 10.5% to $256.8 in premarket trading. The company had a market capitalization of $36.85 billion, as of Thursday's close.

Shares of BridgeBio Pharma BBIO.O, which is also developing a rival drug, jumped 12% before the bell.

(Reporting by Mariam Sunny in Bengaluru; Editing by Shilpi Majumdar)

((Mariam.ESunny@thomsonreuters.com))