Antiviral drugs are a type of medication used to treat viral infections, including human immunodeficiency virus (HIV), herpes, hepatitis, and flu. They are one type of antimicrobial drugs, a class of medication that fights harmful microorganisms in the body. The other types are antibiotics for bacteria, antifungals for fungal infections, and antiparasitic drugs for parasite infections.
Like the other antimicrobials, antiviral drugs are administered to the patient to treat infection in the body, and are relatively harmless to the patient. Poisons used to kill viruses outside the body are known as viricides. Both antibiotics and antivirals are targeted to act against specific organisms. Both are also subject to drug resistance, in which the target organism develops a resistance against the drug, causing it to become less effective over time.
Antiviral drugs work a bit differently than antibiotics, since viruses and bacteria function in different ways. While most antibiotics destroy bacteria, most antivirals only inhibit the growth of the target virus. Antivirals cannot be used to destroy a virus, because viruses use the cells of the host to replicate, so destroying viral cells would amount to destroying the host's body cells, and would cause more harm than good. Because viruses use the host cells to replicate, antivirals are more complex than antibiotics, and appeared on the pharmaceutical scene relatively late. It was not until the 1980s, when scientists were able to discover the genetic sequences and life cycle of viruses in detail, that antivirals could be reliably produced.
In earlier medicine, viruses could only be prevented through vaccination, but were difficult to treat once infection had occurred. Vaccines usually work by infecting the patient with a weak strain of the target virus, allowing his or her immune system to develop antibodies against the virus that will fight it off when infection occurs. Vaccines are not only ineffective against established viral infections, but also have difficulty addressing rapidly mutating viruses such as influenza.
Unlike bacteria, viruses consist only of a genome, and lack the cellular structures of other organisms, rendering them unable to reproduce on their own. Therefore, they require a host to reproduce. Antiviral drugs target viruses at different stages of their life cycle, inhibiting them from reproducing to stop or slow the spread of infection.
Different antiviral drugs work in different ways. They may target the host cells, making them resistant to viral infection, or they may work on viruses within the host cell, interfering with their reproductive mechanisms to prevent the spread of the virus to new cells. They may also prevent the assembly of viral components into complete viral particles within the host cell or the release of the virus from the host cell.