Anti-viral agents inhibit viral replication rather than eliminating viral particles already present.
The process of viral replication is specific to the type of virus, but in all cases replication is reliant on unique enzymes that are essential for viral replication and are not involved in normal cellular function. Processes unique to viral replication are the best targets for antiviral agents.
Enzymes that are common to cellular metabolism and viral replication can also be targeted in some cases. For example, thymidine kinase is an enzyme utilized in both cellular metabolism and viral replication, and can be exploited to activate antiviral agents.
Viral attachment, penetration, assembly and release processes are catalyzed by cellular enzymes, making it difficult to selectively inhibit these processes without adversely affecting normal cell metabolism.
There are four classes of anti-viral medications:
- Non-nucleoside reverse transcriptase inhibitors
- Nucleoside reverse transcriptase inhibitors (nucleoside analogs)
- Protease inhibitors
- Nucleotide analog reverse transcriptase inhibitors (NtARTIs or NtRTIs)
Each class of drug attacks a different phase in the life cycle of the virus.
Non-nucleoside reverse transcriptase inhibitor (NNRTI):
- Nevirapine [Viramune®]
- Delavirdine [Rescriptor®]
- Efavirenz [Sustiva® and Stocrin®]
NNRTIs bind to reverse transcriptase, blocking DNA polymerase required to convert viral RNA to DNA.
Nucleoside reverse transcriptase inhibitor (NRTI):
- Zidovudine [AZT, ZDV, azidothymidine, Retrovir®]
- Didanosine [ddI, Videx® Videx EC®]
- Zalcitabine [ddC, deoxycytidine, Hivid®]
- Stavudine [d4T, Zerit®, Zerit XR®]
- Lamivudine [3TC, Epivir®]
- Abacavir [ABC, Ziagen®]
- Emtricitabine [FTC, Emtriva®, Coviracil])
NRTIs interrupt the formation of viral DNA from RNA by substituting a look-alike compound (analog) that resembles nucleosides (building blocks) used by the virus to synthesize DNA. DNA cannot be synthesized from the look-alike compound and the virus is blocked from replicating.
Protease inhibitors (PIs):
- Tenofovir [tenofovir disoproxil fumarate, Viread®]
- Adefovir [bis-POM PMPA, Preveon® and Hepsera®])
