Merck to Cushion Patent Loss With Prometheus Acquisition (2)

Merck & Co. will buy Prometheus Biosciences Inc. for about $10.8 billion to bolster its research pipeline and strengthen its portfolio of autoimmune drugs.

The agreement to buy the biotech company is one of the largest pharma deals in recent history and comes as Merck’s blockbuster cancer drug Keytruda faces the expiration of its patents.

A Merck unit will acquire all outstanding shares of Prometheus at $200 each in cash, a 75% premium to Friday’s close, according to termsannounced Sunday. Prometheus surged 69% as of 9:49 a.m. in New York, though it traded slightly below the offer price. Merck’s ...