Zalcitabine (2′-3′-dideoxycytidine, ddC), also called dideoxycytidine, is a nucleoside analog reverse-transcriptase inhibitor (NRTI) sold under the trade name Hivid.

Zalcitabine appears less potent than some other nucleoside RTIs, has an inconvenient three-times daily frequency and is associated with serious adverse events.

[4] Resistance to zalcitabine develops infrequently compared with other nRTIs, and generally only occurs at a low level.

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.

[6] Zalcitabine was first synthesized in the 1960s by Jerome Horwitz[7][8] and subsequently developed as an anti-HIV agent by Samuel Broder, Hiroaki Mitsuya, and Robert Yarchoan at the National Cancer Institute (NCI).