elvucitabine is a deoxycytidine analogue with activity against hiv resistant to several other nucleoside analogues, including zidovudine and lamivudine. this is partly because of high intracellular levels of its triphosphate metabolite reached in cells. clinical trials of elvucitabine are on hold, because it has shown bone marrow suppression in some patients, with cd4+ cell numbers dropping as early as two days after initiation of dosing. amdoxovir (dapd) amdoxovir is a guanosine analogue nrti prodrug that has good bioavailability. it is deaminated intracellularly by adenosine deaminase to dioxolane guanine (dxg). dxg-triphosphate, the active form of the drug, has greater activity than dapd-triphosphate. amdoxovir is currently in phasa ii clinical trials. racivir (rcv) racivir is a racemic mixture of the two β-enantiomers of emtricitabine (ftc), (-)-ftc and (+)-ftc. racivir has excellent oral bioavailability and has the advantage of needing to be taken only once a day. racivir can be considered to be used in combination of two nrtis and has shown promising antiviral activity when used in combination. racivir is currently in phase ii clinical trials. table 5 several drug candidates that are undergoing clinical development drug candidate apricitabine elvucitabine amdoxovir racivir chemical structure phase of development final stage of clinical development on hold phase ii phase ii there are several more nrtis in development. either the sponsors have filed for an investigational new drug (ind) application, the application has been approved by the fda or the drugs are in different phases of clinical trials. some of the nrtis that are in development exhibit various attractive pharmacological properties that could make them desirable for the treatment of patients in need of new agents.