Pfizer has terminated development of its RSV treatment candidate sisunatovir, a viral inhibitor picked up in its up to $525 million acquisition of ReViral in 2022.
The New York drug company — which is facing an activist investor that’s expected to call for major changes at the company — ended a Phase 2/3 trial and a Phase 1 study of the oral inhibitor, according to updates to a federal clinical trials database.
“There have been ongoing challenges in the sisunatovir clinical development program, including a drug-drug interaction with antacids,” a Pfizer spokesperson said in an emailed statement to Endpoints News. “While Pfizer has been working diligently to resolve the challenges, we decided to stop the development of sisunatovir.”
The company will now focus on “identifying and advancing the development of other investigational therapeutics that have the greatest potential to prevent and treat RSV disease and other viral respiratory pathogens,” the spokesperson said.
The cull wasn’t because of safety issues, Pfizer said.
The drug, which has FDA fast track designation for both pediatric and adult indications, was still listed on Pfizer’s latest quarterly update in July and still appears on its pipeline page.
With the ReViral deal, Pfizer was hoping to be able to both prevent RSV with its vaccine, and treat it with sisunatovir — much as it did for Covid-19 with a vaccine and antiviral pill. And when the companies announced the deal in 2022, then-ReViral CEO Alex Sapir called Pfizer “an optimal partner given their commitment to RSV.”
At the time, Pfizer said it expected ReViral’s programs to bring in annual revenue of $1.5 billion or more.
Pfizer is one of three pharma companies to market a vaccine for respiratory syncytial virus. The company makes Abrysvo, which was approved in 2023, while Moderna sells mResvia and GSK markets Arexvy. This season’s vaccine uptake has been slower than projected, Wall Street analysts have said.
ReViral was one of many targets on which Pfizer has spent its Covid-19 cash. It acquired cancer drug developer Seagen for $43 billion, $11.6 billion to get migraine drugs from Biohaven, and $6.7 billion for Arena Pharmaceuticals and its immuno-inflammatory programs. It also spent $5.4 billion for sickle cell biotech Global Blood Therapeutics — only to pull the main product behind the deal for safety reasons.