Which of the following antiviral agents is classified as a class of nucleoside analogs?

Lamivudine is classified as a nucleoside analog, which is important in the context of antiviral therapy. Nucleoside analogs mimic the structure of naturally occurring nucleosides, which are the building blocks of nucleic acids like DNA and RNA. By incorporating themselves into the viral nucleic acids during replication, these agents disrupt normal viral genome synthesis, leading to termination of the chain and ultimately inhibiting viral replication.

Lamivudine specifically targets hepatitis B virus (HBV) and human immunodeficiency virus (HIV). This broad-spectrum activity makes it a crucial agent in the management of these infections. Its action is effective because it interferes with the reverse transcriptase enzyme, which is vital for the replication of retroviruses such as HIV.

The other agents listed are not classified as nucleoside analogs. Emtricitabine also belongs to the same class as Lamivudine and acts similarly. Saquinavir and Ritonavir, in contrast, are protease inhibitors that function by blocking the protease enzyme necessary for viral protein maturation, which is a different mechanism from that of nucleoside analogs. Understanding these classifications helps in recognizing how different antiviral agents operate within therapeutic protocols.