ViiV Healthcare filed a patent infringement complaint against Gilead’s new HIV drug Biktarvy on the same day the combination drug secured the FDA’s approval.

In its complaint, ViiV, a joint venture between GlaxoSmithKline, Pfizer and Shionogi, claims Biktarvy infringes on its patent for Tivicay (dolutegravir), which earned GSK about $5.6 billion in fiscal 2017. Dolutegravir is the leading prescribed core agent for HIV treatment.

Biktarvy combines a new integrase inhibitor with Gilead’s Descovy (emtricitabine and tenofovir alafenamide). Gilead filed its own patent application more than three months after the dolutegravir chemical structure was made public, according to the complaint.