Another uses the newest nucleoside analogue, Ziagen, for a total of three RTIs. In addition, PIs have a weakness of cross-resistance. For a while, some scientists thought that cocktails might push HIV out of a person's body. We now see that this probably won't work. We've learned that it may not be necessary to hold the virus completely below the limits of detection.
Scientists also continue to work on a new drug from another new class, integrase inhibitors.
Unfortunately, so far, tests suggest that these drugs are difficult to make, and don't work as well as hoped. Early in the years of our war on HIV, scientists tried to stop HIV at Step 1, before it crossed the moat. Science moved to working on protecting the door, because it was easier to develop medicines at this step. Then three years ago, researchers were startled to discover a few individuals who were virtually immune to traditional modes of HIV transmission, despite numerous exposures to the virus. They were born with pieces missing in their immune system.