Antiviral drugs: Function and Types

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Viral infections are extremely common and widespread infections caused by viruses. There are many varieties of viruses that causes types of viral diseases. For instance, the most common type of viral disease is the common cold, influenza (flu), etc. Treatment of viral infection varies depending on the different virus and other several factors. Certain medications have been introduced like antiretroviral medicines and antiviral drugs. Antiviral drugs are used to minimize the severity of viral infections more specifically in people with high risk or critical stages.

An antiviral drug is a drug that blocks virus reproduction but was also thought to be toxic for people using it. Another key point is that ever since the successful introduction of antibiotics in the 1940s to control bacterial infections, scientists have seen the hope of similar treatment for viral infections using antiviral drugs.

However, antiviral drugs were slow to arrive but for now, we have 40 antiviral drugs which are approved for human use, out of which half of them are specially for HIV-1. Antiviral drugs are specific for one or a few viruses, their treatment does not have a broad spectrum like antibiotics.

Benefits of Antiviral drugs

To begin with, studies have shown that Antiviral treatment works best when started soon after getting infected. Works Best for treatment if started within two days of infection. Although starting them later will still be beneficial especially for the patients at high risk of serious infection, it will reduce the symptoms to mild.

How long one can take Antiviral drugs

All things considered, the longevity of any treatment depends particularly on the severity and the viral infection by which the person is infected. It is advised to take any kind of antiviral drug after consulting with a good physician.  For instance, Oseltamivir is an antiviral drug usually prescribed for 5 days also known as inhaled zanamivir.

image source: Behl, T., Rocchetti, G., Chadha, S., Zengin, G., Bungau, S., Kumar, A., … & Montesano, D. (2021). Phytochemicals from plant foods as potential source of antiviral agents: An overview. Pharmaceuticals, 14(4), 381.

Some antiviral drugs approved for clinical use

Inhibitors of attachment

  • Synagis; RespiGam

Usage– Synagis is an antiviral drug used to treat life-threatening respiratory infections of infants born prematurely at or before 35 weeks.

 Mode of action– Neutralizing IgG specific for the human respiratory syncytial virus fusion protein.

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  • Pleconaril

Usage– this antiviral drug is used against several picornaviruses of the family piconaviridae.

Mode of action– it binds to a hydrophobic pocket on the virion that the cell receptor normally recognizes and blocks.

Antiviral drugs Pleconaril

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Inhibitors of viral fusion

  • Enfuvirtide (T-20)

Usage– HIV-1

Mode of action– A gp41-derived peptide that binds gp41 and inhibits the fusion of viral and cell membrane. Moreover, acts after the virus binds to CD4 receptors and prevents the release of viral nucleic acid into the host cell.

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Inhibitors of virus replication

  • Ganciclovir

Usage– HCMV infection of the immunocompromised for example AIDS

Mode of action– Nucleoside analog similar to guanosine, but contains an acyclic. Sugar group. Activation of the drug requires the presence of three kinases in the cell to convert acyclovir to a triphosphate derivative, the actual antiviral compound. Also, aciclovir is toxic for herpes simplex virus-infected cells but not noninfected cells. The first kinase which converts acyclovir to monophosphate is not found in the uninfected cell. Thus, acyclovir has no effect on host DNA replication because it cannot be phosphorylated and incorporated into host DNA. The virus, however, encodes a kinase that phosphorylates the prodrug to produce acyclovir monophosphate. As acyclovir lacks the 3’ hydroxyl group of the sugar ring, the growing chain terminates.

Antiviral drugs Ganciclovir

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  • Adefovir (PMEA)

Usage– Hepatitis B virus

Mode of action– a competitive inhibitor of reverse transcriptase and chain terminator

Antiviral drugs Adefovir

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Ion channel blockers

  • Amantadine, rimantadine

Usage– Type A influenza virus

Mode of action– Blocks the M2 proton channel in the virion envelope, so that protons cannot enter the virion, preventing the uncoating of the influenza virus. Moreover, amantadine can not affect type B influenza viruses as they do not have an M2 proton channel.

Antiviral drugs Amantadine, rimantadine

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Inhibitors of protease activation of viral proteins

  • Lopinavir, ritonavir

Usage– HIV-1; used in “triple therapy” in combination with nucleoside analogues; retard virus replication and progress to AIDS

Mode of action– Prevent post-transitional cleavage of structural protein precursors.

Inhibitors of virus release from host cells

  • Zanamivir(inhaled) and Oseltamavir(oral)

Usage– Influenza A and B viruses; only effective if taken before infection or shortly after infection.

Mode of action– Analogs of the viral neuraminidase (NANA). It particularly prevents progeny virus from detaching from the cell in which it was made and hence transmission of infection to other healthy cells.

Killing the infected cell

  • Interferon-ALPHA

Usage– effective in vivo only against selected infection: chronic hepatitis B and C.

Mode of action– Upregulates MHC class 1 and facilitates the action of CD8+ cytotoxic cells.

To conclude, there is an ongoing situation of increasing viral infections along with the COVID-19 pandemic. Thus, research about antiviral drugs should increase. Hope this article helped you learn about antiviral drugs. Keep reading!

Team MBD

Check out- Antiviral Drugs – Physiopedia (


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