Cidara Therapeutics Stock Soars 42% After-Hours On Merck Buyout Buzz — Retail Traders Eye A Potential Blowout Premium

• Merck reportedly edged out another bidder in late-stage talks that could lead to a deal announcement as soon as Friday.
• Cidara’s CD388 flu antibody, now in phase 3 trials with FDA breakthrough status, has driven significant takeover interest.
• Retail traders debated whether the move signals a full buyout or a milestone-based deal structure.

Cidara Therapeutics’ shares surged 42% after hours on Thursday following reports that Merck is close to acquiring the biotech in a deal that could be announced as soon as Friday. 

The negotiations reportedly extended late into Thursday as Merck competed with another pharmaceutical group before the seller ultimately favored its offer. The deal is expected to value Cidara above its roughly $3.3 billion market capitalization, though the final price has apparently not been set. Any agreement is likely to include upfront cash and milestone-based payments tied to clinical progress, according to a report by Financial Times.

Big Pharma Races To Rebuild Pipelines

A potential takeover would mark Merck’s latest move to fortify its drug portfolio before Keytruda, its $25 billion-per-year cancer therapy, loses patent protection in 2028. The company agreed in July to buy respiratory drug developer Verona Pharma for $10 billion as part of a broader effort to maintain revenue momentum. The demand for Cidara comes after another big-name auction last week, when Pfizer narrowly won a race against Novo Nordisk for obesity biotech Metsera in a deal worth as much as $10 billion.

Biotech Sector Heats Up As M&A Wave Accelerates

The race for Cidara is unfolding amid a surge in biotechnology dealmaking. The XBI biotech index has gained over 40% in the past six months as investors bet on a return of acquisitions by big drugmakers looking to add next-generation therapies to their pipelines. The scramble reflects rising urgency across the sector as companies face major revenue losses once key products lose exclusivity.

Cidara’s Lead Flu Antibody Drives Takeover Expectations

Cidara’s value surge is tied to its lead program, CD388, a long-acting antibody intended to protect against the two most common strains of influenza. The treatment is being evaluated in phase 3 trials among immunosuppressed patients who cannot receive vaccines, as well as healthy adults over 65. Over 6,000 patients are expected to be enrolled in the studies worldwide by the end of the month. CD388 has been granted an FDA breakthrough designation, which could accelerate regulatory approval. Cidara’s shares have quadrupled since July, driven by strong clinical data and takeover speculation that have fueled investor expectations.

Stocktwits Buzz Highlights Takeover Speculation

On Stocktwits, retail sentiment was ‘extremely bullish’ for Cidara and ‘bullish’ for Merck, with both stocks seeing ‘high’ message volume.

One user reacted to the report by saying, “sounds like $MRK going in for the kill.”

Another user questioned the structure of the potential deal, writing, “It makes me wonder if it is an actual buyout or an investment in the company for rights to their drug? It mentions the possibility of upfront cash plus milestone payments.... hopefully it is a buyout above the current $150 AH price.”

While Cidara’s stock has surged 446% so far in 2025, Merk’s stock has risen 18% over the same period.

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