The prevalent cause of severe human viral diseases.

Uniquely active against RNA viruses.

Nucleic acids are composed of naturally occurring chemical compounds termed nucleosides and nucleotides and are the main information-carrying molecules of the cell that determine the inherited characteristics of human and viral genetic material by directing the process of protein synthesis. The two main classes of nucleic acids are DNA and RNA. Nucleos(t)ide analogs are synthetic compounds that mimic the structure of naturally occurring nucleosides and nucleotides that target the viral polymerase directly so that it mistakenly incorporates these analogs into nascent nucleic acids, causing inhibition of viral replication. Nucleos(t)ide analogs, compared to other classes of antiviral therapies, have a high barrier to viral resistance due to the conservation of the structure of the polymerase that is required to produce viable virions.

Prodrugs are biologically inactive compounds which are employed to improve drug delivery, bypass rate limiting activation steps, decrease toxicity, and improve the oral bioavailability and permeation of cell membranes by the nucleos(t)ide analog.  Prodrugs of nucleos(t)ide analogs have become the backbone of single-drug and combination-drug therapies to treat life threatening viral infections, including HIV, hepatitis B, and hepatitis C.