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.

Boceprevir (trade name Victrelis) is first-generation, selective, small molecule inhibitor of the non-structural serine protease (NS3) and NS4A polypeptide complex (NS3/NS4A) and is a direct acting antiviral drug against the hepatitis C virus. It is indicated the treatment of chronic hepatitis C (CHC) genotype 1 infection, in combination with peginterferon alfa and ribavirin, in adult patients (18 years of age and older) with compensated liver disease, including cirrhosis, who are previously untreated or who have failed previous interferon and ribavirin therapy. Boceprevir is not approved as a monotherapy. Upon administration, boceprevir reversibly binds to the active center of the HCV NS3/NS4A and prevents NS3/NS4A protease-mediated polyprotein maturation. This disrupts the processing of viral proteins and the formation of a viral replication complex, which inhibits viral replication in HCV genotrype 1-infected host cells. NS3, a serine protease, is essential for the proteolytic cleavages within the HCV polyprotein and plays a key role during HCV viral RNA replication. NS4A is an activating factor for NS3.

Telbivudine is an antiviral drug used in the treatment of hepatitis B infection. It is marketed by Swiss pharmaceutical company Novartis under the trade names Sebivo (Europe) and Tyzeka (United States). Clinical trials have shown it to be significantly more effective than lamivudine or adefovir, and less likely to cause resistance. Telbivudine is a synthetic thymidine nucleoside analogue; it is the L-isomer of thymidine. It is taken orally in a dose of 600 mg once daily with or without food. TYZEKA is the trade name for telbivudine, a synthetic thymidine nucleoside analogue with activity against hepatitis B virus (HBV). The chemical name for telbivudine is 1-((2S,4R,5S)-4-hydroxy-5-hydroxymethyltetrahydrofuran-2-y1)-5-methyl-1H-pyrimidine-2,4-dione, or 1-(2-deoxy-β-L-ribofuranosyl)-5-methyluracil. Telbivudine is a synthetic thymidine nucleoside analogue with activity against HBV DNA polymerase. It is phosphorylated by cellular kinases to the active triphosphate form, which has an intracellular half-life of 14 hours. Telbivudine 5'-triphosphate inhibits HBV DNA polymerase (reverse transcriptase) by competing with the natural substrate, thymidine 5'-triphosphate. Incorporation of telbivudine 5'-triphosphate into viral DNA causes DNA chain termination, resulting in inhibition of HBV replication. Telbivudine is an inhibitor of both HBV first strand (EC50 value = 1.3 ± 1.6 µM) and second strand synthesis (EC50 value = 0.2 ± 0.2 µM). Telbivudine 5'-triphosphate at concentrations up to 100 µM did not inhibit human cellular DNA polymerases α, β, or γ. No appreciable mitochondrial toxicity was observed in HepG2 cells treated with telbivudine at concentrations up to 10 µM.

BARACLUDE® is the tradename for entecavir, a guanosine nucleoside analogue with selective activity against hepatitis B virus (HBV). It inhibits all three steps in the viral replication process. By competing with the natural substrate deoxyguanosine triphosphate, entecavir functionally inhibits all three activities of the HBV polymerase (reverse transcriptase, rt): (1) base priming, (2) reverse transcription of the negative strand from the pregenomic messenger RNA, and (3) synthesis of the positive strand of HBV DNA. Upon activation by kinases, the drug can be incorporated into the DNA which has the ultimate effect of inhibiting the HBV polymerase activity. Entecavir is used for the treatment of chronic hepatitis B virus infection in adults with evidence of active viral replication and either evidence of persistent elevations in serum aminotransferases (ALT or AST) or histologically active disease.

The potential antiviral effect of adefovir, an acyclic nucleoside phosphonate analog of 2′-deoxyadenosine monophosphate, was first studied by Holý and De Clercq in 1980s. Adefovir is an acyclic nucleotide analog of adenosine monophosphate which is phosphorylated to the active metabolite adefovir diphosphate by cellular kinases. Adefovir diphosphate inhibits HBV DNA polymerase (reverse transcriptase) by competing with the natural substrate deoxyadenosine triphosphate and by causing DNA chain termination after its incorporation into viral DNA. Oral adefovir dipivoxil is effective and generally well tolerated in HBeAg-positive and -negative patients chronically infected with wild-type or lamivudine-resistant HBV.

(R)-9-(2-Phosphonylmethoxypropyl)adenine (PMPA known as tenofovir) is an antiviral drug. Diphosphate of PMPA acts as a selective inhibitor of the HIV-1 reverse transcriptase. Tenofovir disoproxil was approved for clinical use for the treatment of HIV infection (AIDS) and chronic HBV infection.

Daclatasvir (BMS-790052) is a direct-acting antiviral agent against Hepatitis C Virus (HCV) used for the treatment of chronic HCV genotype 3 infection. Daclatasvir prevents RNA replication and virion assembly by binding to NS5A, a nonstructural phosphoprotein encoded by HCV. Binding to the N-terminus of the D1 domain of NS5A prevents its interaction with host cell proteins and membranes required for virion replication complex assembly.