It used to dominate the market but ViiV's 2014 sales of 1.5 billion pounds were less than a quarter of the HIV revenue generated by market leader Gilead Sciences ViiV will pay an initial $317 million to buy late-stage HIV drug candidates from Bristol-Myers, including a phase III development treatment fostemsavir, plus $33 million for its preclinical assets. HIV is often treated by mixing at least three medicines together because of the ability of the virus that causes AIDS to mutate and become drug-resistant.