US pharmaceutical company Merck & Co Inc (NYSE:MRK), known as MSD outside the US and Canada, on Friday announced a definitive agreement to acquire Cidara Therapeutics Inc (Nasdaq:CDTX), a biotechnology company developing drug-Fc conjugate (DFC) therapeutics.

Under the agreement, a subsidiary of Merck will acquire Cidara for USD221.50 per share in cash, valuing the transaction at approximately USD9.2bn.

The deal aligns with Merck's science-led business development strategy and expands its pipeline with Cidara's late-stage antiviral candidate.

Cidara's lead asset, CD388, is a long-acting, strain-agnostic antiviral designed to prevent influenza A and B in individuals at higher risk of complications. CD388 is in Phase 3 development and has received Breakthrough Therapy and Fast Track designations from the US Food and Drug Administration based on supportive Phase 2b data.

Merck highlighted the strategic importance of CD388 in addressing the persistent global health burden of influenza, particularly among older adults and immunocompromised patients.

The boards of both companies have approved the transaction, which remains subject to a tender offer, regulatory clearances, and customary closing conditions.

Merck expects the acquisition to close in the first quarter of 2026.