Lamivudine is a reverse transcriptase inhibitor used alone or in combination with other classes of anti-human immunodeficiency virus (HIV) drugs in the treatment of HIV infection. This molecule has two stereo-centers, thus giving rise to four stereoisomers: (+/-)-cis-lamivudine and (+/-)-trans-lamivudine. The latter is considered to be impurity of the pharmaceutically active isomer, (-)-cis-lamivudine.

Zidovudine is a nucleoside reverse transcriptase inhibitor (NRTI) with activity against Human Immunodeficiency Virus Type 1 (HIV-1). Zidovudine is phosphorylated to active metabolites that compete for incorporation into viral DNA. They inhibit the HIV reverse transcriptase enzyme competitively and act as a chain terminator of DNA synthesis. The lack of a 3'-OH group in the incorporated nucleoside analogue prevents the formation of the 5' to 3' phosphodiester linkage essential for DNA chain elongation, and therefore, the viral DNA growth is terminated. Zidovudine, a structural analog of thymidine, is a prodrug that must be phosphorylated to its active 5′-triphosphate metabolite, zidovudine triphosphate (ZDV-TP). It inhibits the activity of HIV-1 reverse transcriptase (RT) via DNA chain termination after incorporation of the nucleotide analogue. It competes with the natural substrate dGTP and incorporates itself into viral DNA. It is also a weak inhibitor of cellular DNA polymerase α and γ. Zidovudine is used in combination with other antiretroviral agents for the treatment of human immunovirus (HIV) infections. Zidovudine is marketed as Retrovir.

Trifluridine (also called trifluorothymidine or TFT) is an anti-herpesvirus antiviral drug, used primarily on the eye. It was sold under the trade name, Viroptic, by Glaxo Wellcome, now merged into GlaxoSmithKline. It is a nucleoside analogue, a modified form of deoxyuridine, similar enough to be incorporated into viral DNA replication, but the -CF3 group added to the uracil component blocks base pairing, thus interfering with DNA replication. It is a component of the experimental anti-cancer drug TAS-102. Trifluridine is a fluorinated pyrimidine nucleoside with in vitro and in vivo activity against herpes simplex virus, types 1 and 2 and vaccinia virus. Some strains of adenovirus are also inhibited in vitro. VIROPTIC is also effective in the treatment of epithelial keratitis that has not responded clinically to the topical administration of idoxuridine or when ocular toxicity or hypersensitivity to idoxuridine has occurred. In a smaller number of patients found to be resistant to topical vidarabine, VIROPTIC was also effective. The mechanism of action of trifluridine has not been fully determined, but appears to involve the inhibition of viral replication. Trifluridine does this by incorporating into viral DNA during replication, which leads to the formation of defective proteins and an increased mutation rate.