Lopinavir HIV drug-protease complex. Computer model showing a molecule of the anti-HIV (human immunodeficiency virus) drug lopinavir (spheres) complexed with a protease enzyme molecule (ribbons). The beta sheet structure of the enzyme is shown. HIV is the virus that causes AIDS (acquired immune deficiency syndrome). HIV uses protease enzymes to assemble its virions in the host cell after reproduction. Lopinavir is a protease inhibitor drug and so prevents this assembly and slows, or even halts, the progress of the disease. Lopinavir has also been found to be affective against strains of human papilloma virus (HPV) that cause cervical cancer.