41. Nucleoside reverse transcriptase inhibitor (NRTI), non-nucleoside reverse transcriptase inhibitor (NNRTI) and protease inhibitor (PI) classes prevent the replication of HIV by working inside CD4 cells after they have been infected with HIV. The drugs in these three classes then target specific steps in the replication process to prevent the creation of new HIV particles. Fusion inhibitors differ from these drugs because they work on the outside of the cell to prevent HIV from fusing with, and infecting the CD4 cells in the first place. from Fuzeon.com www.freelivedoctor.com