KP-1461 is a prodrug of KP-1212 triphosphate, a unique nucleoside that is incorporated into the HIV viral genome resulting in an accumulation of nucleic substitutions that interfere with viral replication. The study is designed to investigate the safety and antiviral activity for 124 days in antiretroviral-experienced HIV-1-infected subjects. By inducing additional mutagenic events in the viral genome, viral decay accelerators such as KP-1212 may force the virus to exceed the threshold of nonviability.