A 29-year-old woman is tested positive for human immunodeficiency virus type 1 (HIV-1) antibody during a routine annual check-up with her gynecologist. She is asymptomatic and has a normal physical examination. Her CD4 cell count is 325 cells per mm3 confirmed on repeated testing She receives HIV drug combination for treatment of her condition. Which one of the following drugs is the backbone with other regimen in the treatment of this patient?