Merck & Co. has agreed to acquire Cidara Therapeutics for approximately $9.2 billion, the companies said, in a deal designed to bolster the buyer’s antiviral pipeline with a Phase III drug designed to prevent influenza in individuals at higher risk of complications.
That Phase III drug—Cidara’s lead pipeline candidate CD388—is a long-acting antiviral designed to achieve universal prevention of seasonal and pandemic influenza. CD388 consists of a small molecule neuraminidase inhibitor stably conjugated to a proprietary Fc fragment of a human antibody designed to prevent influenza A and B.
CD388 is now under study in the Phase III ANCHOR trial (NCT07159763), which is assessing the drug among adult and adolescent participants deemed to be at higher risk of developing complications from influenza.
“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,” Robert M. Davis, Merck’s chairman and CEO, said in a statement.
Merck’s plan to acquire Cidara comes four months after Cidara announced positive topline results from its Phase IIb NAVIGATE trial (NCT06609460) showing CD388 to have met all primary and secondary endpoints associated with preventing symptomatic laboratory-confirmed influenza in healthy unvaccinated adults ages 18–64.
Significant prevention efficacy
NAVIGATE results showed a statistically significant prevention efficacy (PE) for each of three dose groups in individuals who received a single dose of CD388 at the beginning of the flu season and were evaluated for laboratory and clinically confirmed influenza over 24 weeks. PE ranged from 57.7% among the 1,175 participants given the low (150 mg) dose of CD388, to 76.1% among the 1,187 high dose (450 mg) participants.
The study also met all secondary endpoints, including efficacy at 37.8- and 37.2-degree Celsius temperature thresholds, as well as maintenance of PE up to 28 weeks with statistical significance.
“Thanks to the extraordinary dedication of our team, the Phase IIb NAVIGATE study delivered compelling results that demonstrate CD388’s potential to provide an additional option to vaccines and antivirals to help address unmet needs in influenza prevention,” stated Jeffrey Stein, PhD, Cidara’s president and CEO. “[Merck]’s global development, regulatory and commercial capabilities provide the expertise and resources needed to bring this important innovation to those individuals who need it most.”
In September, Cidara launched its Phase III ANCHOR trial (NCT07159763), a randomized, double-blind, placebo-controlled study designed to evaluate the safety and efficacy of CD388 for the prevention of influenza in adults and adolescents at higher risk of developing influenza complications.
ANCHOR’s first participants were dosed in September, with enrollment proceeding in 150 sites across the United States and the United Kingdom. The study has a target enrollment of 6,000 participants, with plans for an interim analysis in the first quarter of 2026 to determine the potential need for additional enrollment.
Last month, Cidara won an up to $339.2 million award (contract number 75A50125C0017) from the Biomedical Advanced Research and Development Authority (BARDA). The award’s base period funding of $58.1 million over an initial 24 months is intended to support the manufacturing of CD388 in the United States. CD388 has also received the FDA’s Breakthrough Therapy and Fast Track designations.
“This acquisition expands and complements our respiratory portfolio and pipeline,” added Dean Y. Li, MD, PhD, president, Merck Research Laboratories.
Recouping revenue
The Cidara acquisition is Merck’s latest effort to recoup the billions of dollars in sales it will lose as its aging blockbusters lose patent exclusivity in the coming years. Those aging blockbusters include the multi-indication cancer immunotherapy Keytruda® (pembrolizumab), which generated $23.303 billion in the first three quarters of this year, on top of $29.482 billion in all of 2024—topping GEN’s A-List of Top 10 Best Selling Drugs, published earlier this year.
Also set to lose patent protection within Merck’s portfolio:
- Gardasil® and Gardasil 9 [Human Papillomavirus Quadrivalent (Types 6, 11, 16, and 18) Vaccine, Recombinant] and Gardasil 9 (Human Papillomavirus 9-valent Vaccine, Recombinant)], $4.202 billion in Q1–Q3 2025 and $8.583 billion in 2024 (Merck reports only combined revenue for both products)
- Januvia® (sitagliptin), $1.302 billion and $1.334 billion
- Janumet® and its extended-release version Janumet® XR (sitagliptin and metformin hydrochloride), $741 million and $935 million
- Lenvima® (lenvatinib), which Merck co-markets with Eisai, $781 million and $1.010 billion, recorded as “alliance” revenue representing Merck’s share of profits (consisting of product sales net of cost of sales and commercialization costs)
- Lynparza® (olaparib), which Merck co-markets with AstraZeneca, $1.061 billion and $1.311 billion, recorded as alliance revenue, representing Merck’s share of profits
As with other pharma giants facing the proverbial “patent cliff”, Merck is eager to add new treatments to its marketed portfolio and clinical pipeline.
On October 7, Merck completed its $10 billion purchase of Verona Pharma, a deal designed to expand the pharma giant’s pipeline and portfolio of cardio-pulmonary disease treatments. The deal added to Merck’s portfolio the marketed drug Ohtuvayre® (ensifentrine), which won FDA approval last year as a maintenance treatment for chronic obstructive pulmonary disease (COPD) in adults, and is being assessed in clinical trials as a potential treatment for non-cystic fibrosis bronchiectasis.
Based in San Diego, Cidara uses its Cloudbreak® platform to develop drug-Fc conjugate (DFC) therapeutics designed to inhibit specific disease targets while simultaneously engaging the immune system.
Investors roared their approval of Merck’s buying out Cidara by sending Cidara’s shares more than doubling on Friday, a 105% surge that rocketed the company’s shares traded on NASDAQ to $217.71 at the close of trading. Merck shares on the New York Stock Exchange closed unchanged at $92.93 on Friday.
Through a subsidiary, Merck plans to acquire all outstanding shares of Cidara for $221.50 per share cash—a 109% premium to Cidara’s Thursday closing price of $105.99. The acquisition is subject to a majority of Cidara’s stockholders tendering their shares in a tender offer.
The boards of Merck and Cidara have approved the transaction. The deal is expected to close in the first quarter of 2026, subject to the expiration of the waiting period under the Hart-Scott-Rodino Antitrust Improvements Act and other customary conditions.
“This milestone represents a transformational moment for Cidara and for our mission to redefine influenza prevention,” Stein added.
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