This is a picture of HIV and AIDS drugs known as protease inhibitors (PI). They were first approved in 1995. Protease inhibitors, as the name says, inhibit protease. Almost every living cell contains protease. Protease is a digestive enzyme that breaks down protein and is one of the many enzymes that HIV uses to reproduce itself. The protease in HIV attacks the long healthy chains of enzymes and proteins in the cells and cuts them into smaller pieces. These infected smaller pieces of proteins and enzymes continue to infect new cells. The protease inhibitors take effect before the protease in HIV has the chance to break down the protein and enzymes. This way the protease inhibitors slow down the duplication of the virus and thus prevent the infection of new cells. The NRTIs and NNRTIs only have an effect on newly infected cells. Protease inhibitors are able to slow the process of immature non-infectious virus becoming mature and infectious. Protease inhibitors also work in cells that have been infected for a long time, by slowing down the reproduction of the virus.