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FDA casts doubt on Alnylam drug trial results for expanded usage

Signage outside the Alnylam Pharmaceuticals office in the Kendall Square neighborhood of Cambridge, Mass. on Sept. 6, 2022.Adam Glanzman/Bloomberg

US regulators questioned the effectiveness of a drug made by Alnylam Pharmaceuticals Inc. as the company seeks approval for expanded use in treating a heart muscle disease called cardiomyopathy.

Onpattro’s effects compared to a placebo “were small, of questionable clinical meaningfulness, and may not be detectable by patients,” the US Food and Drug Administration wrote in documents posted Monday ahead of a meeting with Alnylam and expert advisors later this week. There were no major safety issues identified.

The drug, the company’s second best-selling, was initially approved in 2018 as a first-of-its-kind treatment for a rare genetic disease called polyneuropathy that is characterized by the buildup of abnormal amyloid protein in peripheral nerves, the heart and other organs. Onpattro is given as an infusion and was the first in a class of drugs called small interfering ribonucleic acid, or siRNA, treatments to be approved by the FDA.


A group of FDA advisors will meet Wednesday to discuss evidence from the small trial submitted by Alnylam to support Onpattro’s use in improving symptoms from a specific type of cardiomyopathy that’s also caused by the build-up of amyloid protein in the heart, which can lead to heart failure. The FDA will likely make its decision on whether to approve the drug’s expanded usage by early next month.

Despite the findings, RBC Capital Markets analyst Luca Issi said he expects the drug to get the FDA’s approval. “We are not surprised by mixed briefing documents and remain confident that the drug ultimately gets approved given the drug is safe” and hit primary and secondary endpoints, Issi wrote in a note.

An estimated 50,000 patients around the world have the genetic form of the disease. The wild-type, which mostly affects older men, may be even more common and is likely under-diagnosed.

Pfizer Inc.’s Vyndaqel and Vyndamax are the only medications approved to treat adults with this form of cardiomyopathy.


Alnylam’s shares rose 0.6 percent at 11:39 a.m. in New York.

With assistance from Robert Langreth.