Zalcitabine is a nucleoside analog reverse transcriptase inhibitor (NARTI). Zalcitabine is a potent inhibitor of HIV replication at low concentrations, acting as a chain-terminator of viral DNA by binding to reverse transcriptase. Zalcitabine is phosphorylated in T cells and other HIV target cells into its active triphosphate form, ddCTP. This active metabolite works as a substrate for HIV reverse transcriptase, and also by incorporation into the viral DNA, hence terminating the chain elongation due to the missing hydroxyl group. Since Zalcitabine is a reverse transcriptase inhibitor it possess activity only against retroviruses.