Fighting Viruses: How Do Antivirals Work?

Rather than killing a virus directly, antivirals usually suppress the virus's ability to infect and multiply in your cells. These drugs often work by inhibiting molecular interactions and functions needed by the virus to produce new copies of itself.

The way a drug produces its therapeutic effect is called its mechanism of action. Antivirals are often delivered in combinations that have different mechanisms of action. This helps to prevent the emergence of mutated drug-resistant viral strains that can bypass the effects of a single drug. For example, combination antiviral therapy is now the standard of care in HIV and hepatitis C virus infections. It is highly desirable to develop multiple antivirals whenever possible.

The development of antivirals can be challenging. Because viruses are parasites that hijack host cell machinery, care must be taken to select drug targets that interfere with viral replication while causing as little harm to healthy host cells as possible. Like vaccines, antivirals must go through a multistep approval process by the U.S. Food and Drug Administration (FDA).

Is there an antiviral treatment for COVID-19?

Historically, antiviral therapy has been available only for a limited number of infections, including those caused by HIV, herpes, hepatitis B and C, and influenza A and B. Drug companies and researchers investigated new and existing antivirals for potential use in treating COVID-19, and some candidates have proven effective in clinical trials.

Several countries have approved the use of the drug Veklury (remdesivir) for certain patients. For example, in October, 2020, the U.S. Food and Drug Administration (FDA) approved it for qualified patients who have been hospitalized as a result of COVID-19. Veklury is administered via injection and is limited to hospital or comparable healthcare settings.

In December, 2021, the FDA granted emergency use authorization for Paxlovid (nirmatrelvir co-packaged with ritonavir) and molnupiravir, orally administered drugs that can be taken at home.

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