LONDON (AP) — Shares in Anglo-Swedish drugmaker AstraZeneca jumped 15 percent on Monday after U.S. pharmaceutical firm Pfizer said it offered to buy the company for around $100 billion.

Pfizer, the maker of Viagra, said that AstraZeneca rejected an initial approach in January valuing the company at about 59 billion pounds ($100 billion). The cash and shares deal would represent a 30 percent premium on AstraZeneca’s closing share price of 35.26 pounds on Jan. 3, around the time the offer was made.