Viruses are obligate intracellular parasites that invade host cells and hijack their machinery to replicate. Antiviral drugs work by inhibiting viral replication and development inside host cells. There are several classes of antiviral drugs including adamantane derivatives, purine nucleotides, and pyrimidine nucleotides. Acyclovir, a purine nucleotide, gets activated by viral thymidine kinase inside infected cells and competitively inhibits viral DNA polymerase or gets incorporated into viral DNA. Idoxuridine, a pyrimidine nucleotide, is phosphorylated and substitutes for thymidine during viral DNA synthesis, inhibiting the viral DNA polymerase enzyme. Antiviral drugs display specificity against certain viruses by exploiting differences between host and viral polymer