What class of agents does Sofosbuvir belong to?

Sofosbuvir is classified as a direct-acting antiviral agent because it specifically targets the hepatitis C virus (HCV) by inhibiting the viral RNA polymerase, known as NS5B. This action directly interferes with the replication of the virus, making it effective as a treatment for HCV. Unlike other antiviral agents that may work on a more broad or indirect basis, direct-acting antivirals focus on key viral proteins or enzymes to disrupt the replication cycle of the virus.

The other classes mentioned, such as nucleotide reverse transcriptase inhibitors, fusion inhibitors, and integrase inhibitors, are primarily used for the treatment of HIV and other viral infections, and they function through different mechanisms. Nucleotide reverse transcriptase inhibitors work by blocking reverse transcription, while fusion inhibitors prevent the virus from entering host cells. Integrase inhibitors target the integrase enzyme necessary for integrating viral DNA into the host's genome. Therefore, these mechanisms are not applicable to Sofosbuvir, which is tailored for HCV and exemplifies the targeted nature of direct-acting antivirals.