Antibiotics vs. Antivirals

You may know that we don’t use antibiotics on viral infections, but do you know why? The word antibiotic comes from the Greek language and literally means “against life”. Antibiotics are used to treat bacterial infections, since bacteria are living, single-cell organisms. Each bacterial cell is comprised of an envelope structure that forms the outer layer of the cell and separates the inside of the cell (the cytoplasm) from the exterior environment. The envelope is much like an inflated balloon that keeps the outside air and the inside air separate, except that the envelope is much more complex and dynamic than a balloon. The cell envelope actively allows nutrients to enter and waste to exit, but tries to keep harmful substances out. Inside the cell is the DNA that encodes all the genes, as well as various cellular machinery necessary for life. This machinery includes protein complexes to replicate the DNA, to transcribe the DNA into RNA, and to translate the RNA into new proteins via structures called ribosomes. Antibiotics typically attack the envelope to disrupt its functions or attack the cellular machinery to inhibit their activity, any of which either prevents the cell from replicating or kills it. In contrast, viruses aren’t cells. Viruses lack almost all the features that we use to define living organisms, so it’s debatable about whether or not they are “alive”. Instead, viruses are complex nanomachines that are basically inert until they enter the host’s cells. Viral particles, called virions, don’t have envelopes that function like cellular envelopes, and with rare exceptions don’t have any of the typical cellular machinery that bacteria have. Because viruses lack all the cellular targets, antibiotics have nothing to attack and are thus ineffective against viruses. Fortunately, clinicians have a growing array of drugs that do target specific viral proteins that become expressed once the virus infects a cell. We call these virus-specific drugs antivirals to distinguish them from antibiotics. Like antibiotics, the goal of antiviral drugs is to inhibit viral reproduction by targeting steps that are unique to a particular virus. Conversely, since antiviral drugs target very specific viral functions, they typically have no effect on bacteria. Sometimes when patients have viral infections the physician will prescribe antibiotics, but this is to prevent a secondary bacterial infection, not to treat the viral infection. Always discuss with your doctor when in doubt.

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