Merck has announced a definitive agreement to acquire Cidara Therapeutics for approximately $9.2 billion in cash. The deal is part of Merck's strategy to diversify its portfolio, particularly to counter the upcoming patent expiration of its blockbuster cancer drug, Keytruda, in 2028.

Merck will pay $221.50 per share in cash for Cidara, which represents a premium of approximately 109% over Cidara's closing price on the day prior to the announcement.

The primary asset Merck is acquiring is Cidara's lead candidate, CD388, an investigational, long-acting, strain-agnostic antiviral agent designed for the prevention of influenza in high-risk individuals. CD388 is currently in a Phase 3 clinical trial (the ANCHOR study) and has received FDA Breakthrough Therapy and Fast Track Designations, which could accelerate its development and review process.

“We continue to execute our science-led business development strategy, augmenting our pipeline with CD388, a potentially first-in-class, long-acting antiviral designed to prevent influenza in individuals at higher risk of complications,” said Robert M. Davis, chairman and chief executive officer, Merck. “We intend to build on the Cidara team’s remarkable progress and are confident that CD388 has the potential to be another important driver of growth through the next decade, creating real value for shareholders.”

The transaction has been approved by both companies' boards of directors and is expected to close in the first quarter of 2026, subject to customary closing conditions, including a majority of Cidara's stockholders tendering their shares and expiration of the waiting period under the HSR Act.