Cidara Therapeutics, Inc. (CDTX)

Cidara Therapeutics, Inc. was a clinical-stage biotechnology company based in San Diego, California. It was founded in 2012 and was originally named K2 Therapeutics. The company focused on developing long-acting treatments and preventives for serious infectious diseases and related conditions, and it completed an initial public offering in 2015, with its common stock listed on the Nasdaq under the symbol CDTX.

Its first major program was rezafungin, a once-weekly echinocandin antifungal for serious fungal infections such as candidemia and invasive candidiasis. Rezafungin was approved by the U.S. Food and Drug Administration in 2023 under the brand name Rezzayo. Cidara partnered the product with Mundipharma for commercialization and later reorganized its business around its other research.

Cidara's second area of work was its Cloudbreak platform, which created drug-Fc conjugates, molecules that combine an antiviral compound with an antibody fragment designed to extend activity in the body. The lead candidate from this platform was CD388, an investigational conjugate intended for the prevention of influenza, with the potential for season-long protection. CD388 was studied in clinical trials, including a Phase 3 study in adults and adolescents at higher risk of influenza complications.

As a development-stage company, Cidara depended on partnership revenue and capital raised from investors to fund its research, and it reported net losses in most years. CD388 became the center of its strategy, and interest in the program grew as clinical results were reported during 2025. The company described CD388 as non-vaccine approach that was designed to work regardless of influenza strain.

In November 2025 Merck & Co., Inc. announced an agreement to acquire Cidara through a subsidiary. Merck commenced a tender offer to purchase all outstanding shares of Cidara common stock at $221.50 per share in cash. The tender offer expired at 11:59 p.m. Eastern Time on January 6, 2026, and approximately 27.1 million shares, or about 86 percent of the outstanding shares, were tendered.

Merck completed the acquisition through a merger on January 7, 2026, and Cidara became a wholly owned subsidiary of Merck. Following the closing, the Cidara common stock ceased to be listed on the Nasdaq Global Market. Merck stated that the acquisition would increase its 2026 research and development expenses by approximately $9.0 billion, or about $3.65 per share. Cidara's influenza prevention program thus continues in development under Merck, while the company's stock no longer trades publicly and holders who tendered received cash for their shares.