With sales of its hepatitis C drugs falling and an oncology pipeline that has largely disappointed, bictegravir is vitally important for Gilead to defend and grow its dominant HIV franchise. Bictegravir, the company’s next-generation integrase inhibitor, suppressed the HIV virus in newly diagnosed patients better than dolutegravir, a similar, rival drug from GlaxoSmithKline , according to results from a mid-stage clinical trial announced Monday night.