A synthetic aromatic derivative with antiviral properties. Ritonavir is a peptidomimetic agent that inhibits both HIV-1 and HIV-2 proteases, thereby preventing the cleavage of Gag-Pol polyproteins and resulting in the production of noninfectious viral particles. This agent is more active against HIV-1. Because ritonavir targets the HIV replication cycle after translation and before assembly, it is active in chronically infected cells that generally are not affected by nucleoside reverse transcriptase inhibitors. Check for active clinical trialsusing this agent. or A drug used to treat infection with HIV (the virus that causes AIDS). It is also being studied in the treatment of some types of cancer. Ritonavir blocks the ability of HIV to make copies of itself and may block the growth of cancer cells. It is a type of anti-HIV agent and a type of protease inhibitor. Also called Norvir.