Antiviral Drugs

Antiviral drugs

Antiviral drugs are compounds that are used to prevent or treat viral infections, via the disruption of an infectious mechanism used by the virus, or to treat the symptoms of an infection.

Different types of antiviral drugs have different modes of operation. For example, acyclovir is a drug that is used to treat the symptoms of the infections arising from the herpes virus family. Such infection includes lesions on the genitals, oral region, or in the brain. Acyclovir is also an antiviral agent in the treatment of chickenpox in children and adults, and shingles in adults caused by the reactivation of the chickenpox virus after a period of latency. Shingles symptoms can also be treated by the administration of valacyclovir and famciclovir.

Eye infections caused by cytomegalovirus can be treated with the antiviral agent known as ganciclovir. The drug acts to lessen the further development and discomfort of the eye irritation. But, the drug may be used as a preventative agent in those people whose immune system will be compromised by the use of an immunosupressant.

Another category of antiviral drugs is known as the antiretroviral drugs. These drugs target those viruses of clinical significance called retroviruses that use the mechanism of reverse transcription to manufacture the genetic material needed for their replication. The prime example of a retrovirus is the Human immunodeficiency virus (HIV ), which is the viral agent of acquired immunodeficiency syndrome (AIDS ). The development of antiviral drugs has been stimulated by the efforts to combat HIV. Some anti-HIV drugs have shown promise against hepatitis B virus, herpes simplex virus, and varicella-zoster virus.

The various antiviral agents are designed to thwart the replication of whatever virus they are directed against. One means to achieve this is by blocking the virus from commandeering the host cell's nuclear replication machinery in order to have its genetic material replicated along with the host's genetic material. The virus is not killed directly. But the prevention of replication will prevent the numbers of viruses from increasing, giving the host's immune system time to deal with the stranded viruses.

The incorporation of the nucleotide building blocks into deoxyribonucleic acid (DNA ) can be blocked using the drug idoxuridine or trifluridine. Both drugs replace the nucleoside thymidine, and its incorporation produces a nonfunctional DNA. However, the same thing happens to the host DNA. So, this antiviral drug is also an anti-host drug. Vidarabine is another drug that acts in a similar fashion. The drug is incorporated into DNA in place of adenine. Other drugs that mimic other DNA building blocks.

Blockage of the viral replicative pathway by mimicking nucleosides can be successful. But, because the virus utilizes the host's genetic machinery, stopping the viral replication usually affects the host cell.

Another tact for antiviral drugs is to block a viral enzyme whose activity is crucial for replication of the viral genetic material. This approach has been successfully exploited by the drug acyclovir. The drug is converted in the host cell to a compound that can out compete another compound for the binding of the viral enzyme, DNA polymerase, which is responsible for building DNA. The incorporation of the acyclovir derivative exclusively into the viral DNA stops the formation of the DNA. Acyclovir has success against herpes simplex viruses, and Epstein-Barr virus . Another drug that acts in a similar fashion is famiciclovir.

Other antiviral drugs are directed at the translation process, whereby the information from the viral genome that has been made into a template is read to produce the protein product. For example, the drug ribavirin inhibits the formation of messenger ribonucleic acid .

Still other antiviral drugs are directed at earlier steps in the viral replication pathway. Amantadine and rimantadine block the influenza A virus from penetrating into the host cell and releasing the nuclear material.

Antiviral therapy also includes molecular approaches. The best example is the use of oligonucleotides. These are sequences of nucleotides that are specifically synthesized to be complimentary with a target sequence of viral ribonucleic acid. By binding to the viral RNA , the oligonucleotide blocks the RNA from being used as a template to manufacture protein.

The use of antiviral drugs is not without risk. Host cell damage and other adverse host reactions can occur. Thus, the use of antiviral drugs is routinely accompanied by close clinical observation.

See also Immunodeficiency diseases; Viruses and responses to viral infection