Viruses require host cells to replicate. This can make control of viral replication difficult in some cases. There are several classes of antiviral agents effective against viral replication in the human body. Each class has a different mode of action.

Protease Inhibitors

The protease inhibitor class of antiviral drugs stops viruses from replicating copies capable of infecting the host. These drugs get prescribed as part of a cocktail with other drugs in people who have contracted human immunodificiency virus (HIV).

Nucleoside Reverse Transcriptase Inhibitors

While the previous class works on an enzyme called protease for inhibition of infective viral replication, nucleoside reverse transcriptase inhibitors end the process of DNA replication in the virus, resulting in incomplete genetic information. This causes ineffective virus particles to be reproduced.

Nucleotide Reverse Transcriptase Inhibitors

This class of reverse transcriptase inhibitors (RTI) have the same function as the nucleoside version. In the nucleoside RTI, the nucleoside needs to convert to a nucleotide analog in the body. By taking nucleotide RTIs directly, this conversion step does not need to occur in vivo.

Non-Nucleoside Reverse Transcriptase Inhibitors

Synthesizing DNA from RNA (as retroviruses do) requires an enzyme called reverse transcriptase. The non-nucleoside reverse transcriptase inhibitors prevent this enzyme from converting RNA to DNA.

Fusion Inhibitors

According to Yahoo!Health, fusion inhibitors prevent viruses such as HIV from fusing with the cells in the body. If the virus can't get into the cell, it can't replicate and infect the host.

Source:

Nucleoside Reverse Transcriptase Inhibitors

Yahoo Health: Fusion Inhibitors

More Information:

Viral Replication