Lopinavir HIV drug molecule. Computer model of a molecule of the anti-HIV (human immunodeficiency virus) drug lopinavir. Atoms are represented as spheres and are colour-coded; carbon (blue), hydrogen (gold), oxygen (red) and nitrogen (dark blue). HIV is the virus that causes AIDS (acquired immune deficiency syndrome). Lopinavir belongs to a class of drugs called protease inhibitors. It prevents the assembly or viral proteins into virions in the host cell after replication by inhibiting the enzyme protease. This 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.