Ritonavir is an inhibitor of HIV protease used to treat HIV infection and AIDS. It is now rarely used for its own antiviral activity, but remains widely used as a booster of other protease inhibitors. More specifically, ritonavir is used to inhibit a particular liver enzyme that normally metabolizes protease inhibitors, cytochrome P450-3A4 (CYP3A4). The drug’s molecular structure inhibits CYP3A4, so a low dose can be used to enhance other protease inhibitors. This discovery has drastically reduced the adverse effects and improved the efficacy of PI’s and HAART. | 
