antiviral
Meaning of antiviral: Narrow by design: a drug that halts one virus usually does nothing whatsoever against an unrelated one.
Definition of antiviral
An antiviral is a medication used to treat an infection caused by a virus. Viruses are not cells and cannot copy themselves; they take over the machinery of a living cell instead. Antivirals work by blocking one step of that takeover, such as entry into the cell, copying of the viral genetic material, or the assembly and release of new viral particles.
Where in the viral life cycle do they act?
| Step blocked | What it prevents |
|---|---|
| Attachment and entry | The virus binding to and getting inside a cell |
| Copying the genetic material | New viral genomes being produced |
| Cutting viral proteins to size | Newly made proteins becoming functional |
| Assembly and release | Finished particles leaving to infect further cells |
Each step depends on a viral protein with its own shape, and a drug is built to fit that shape. Since a virus supplies only a handful of its own proteins and borrows the rest from the host cell, the number of targets is small, which is one reason antivirals took far longer to develop than drugs against bacteria.
Why is an antiviral so specific?
The enzyme that copies the genome of hepatitis C virus looks nothing like the one used by influenza A virus, so a drug shaped for one is useless against the other. Even related viruses can differ enough to matter. This is the opposite of the situation with many antibiotics, some of which work across whole groups of unrelated bacteria. It also means the first step in treating a viral illness is usually identifying which virus is present, since the answer determines whether any drug exists for it at all.
Does an antiviral cure the infection?
Sometimes, and sometimes not. Modern direct acting antivirals clear hepatitis C from the body in the great majority of people who complete a course. Drugs for HIV and for hepatitis B virus hold the virus down to undetectable levels and keep the immune system or the liver from further damage, but the virus persists and returns if the drug stops. Herpes viruses hide in nerve cells where no current drug reaches them, so treatment shortens and reduces outbreaks rather than removing the virus. Influenza drugs shorten illness modestly and work best when started early, because by the time symptoms peak much of the viral replication has already happened.
Used in a sentence
An antiviral medication was prescribed shortly after the onset of the influenza symptoms.
Good to know
An antiviral is directed at one virus or a family of related viruses, unlike an antibiotic, which acts against bacteria and has no effect at all on a viral infection.
Word origin
Where “antiviral” comes from
Formed from anti-, Greek for against, and viral, from Latin virus, meaning poison or slimy fluid, a word once applied broadly to infectious agents.