antiviral

An antiviral is a drug that fights a virus by interfering with its ability to copy itself, rather than killing it outright. This is intrinsically hard because viruses are not free-living cells; they slip inside our own cells and borrow our machinery to reproduce. Attacking the virus therefore means finding the few steps that are uniquely viral, so the drug does not simply poison the host.

Antivirals target distinct stages of the viral life cycle. Some block the virus from entering cells, like the HIV drug maraviroc; some inhibit the viral enzymes that copy the genome, such as the reverse transcriptase and protease inhibitors used in HIV, or the polymerase inhibitors acyclovir and remdesivir; and some, like the influenza drug oseltamivir, block release of new virus from infected cells. Most are virustatic, suppressing replication rather than eradicating the virus.

Because antivirals mostly suppress rather than cure, timing and duration matter enormously. Many work best when started very early in infection, before the virus has multiplied widely, and chronic viral infections such as HIV or hepatitis B may require lifelong or prolonged therapy. Viruses also mutate rapidly, so resistance is common, which is why HIV is treated with combinations of agents rather than a single drug.