Abacavir AIDS drug molecule. Computer model of a molecule of the AIDS (acquired immune deficiency syndrome) drug abacavir. The molecule's surface is colour-coded based on the underlying atom: carbon (pink), hydrogen (white), nitrogen (yellow) and oxygen (blue). AIDS is caused by HIV (human immunodeficiency virus). Abacavir belongs to a class of drugs called reverse transcriptase inhibitors (RTIs). These drugs inhibit the activity of the enzyme reverse transcriptase, which HIV needs to transcribe its genetic material (RNA) into the host's DNA so that it can be replicated.