Why can’t I take an antibiotic for my cold: A primer on viruses.

This is another article I put up on my Medium.com account.

 

As I’ve mentioned in a prior post, and is likely noted in other posts on my blog (and numerous medicine related sites), a virus is genetic material — either DNA or RNA — encapsulated in a protein coat. In some cases there is also a lipid envelope around the protein coat.

This gets to the crux of why antibiotics don’t work on viruses. Viruses need a living cell to reproduce, and does so by co opting the metabolic pathways of the host cell it invades. Normal cells use DNA to pass genetic information from one (cell) generation to the next. The DNA gets transcribed into RNA which is then taken to the cytoplasm of the cell (in eukaryotic cells) or other parts of the cell (in bacteria/non eukarotic cells), where proteins and ribosomes/ribosomal RNA read the RNA and ‘transcribe’ it into a protein.

In some cases, viruses do code for novel (relative to cells) enzymes and/or proteins. EG, reverse transcriptase in HIV viruses (HIV is a RNA based virus, but it’s genetic code is converted to DNA for replication). Other viruses replicate the RNA directly for future virus particles. However, as I note above, the vast majority of the replication is done by the cell’s own proteins.

This is why antibiotics don’t work on viruses. Bacteria have have different types of cell walls than human cells. They require chemicals that our cells just don’t use. Penicillins and cephalosporins interfere with the cell wall construction as an example. Other antibiotics target pathways our cells don’t have (eg, trimethaprim-sulfamathoxazole targets folate production in bacteria. Our cells don’t produce folate so it doesn’t affect us). There are other examples that could be used as well that utilize a chemical’s affinity for a bacterial protein/enzyme more than for the equivalent in human cells.

Having said this, there are some antiviral drugs for some (not all) viruses. These target the proteins viruses code for that are novel to the specific virus/virus family.

Now at this point, you might be thinking “well, my great aunt _namehere_ was told she had a viral pneumonia, but when she got admitted to the hospital she was given antibiotics”. In some cases, a viral infection goes through its course and the person can develop a secondary infection that’s bacterial in nature. In that case, antibiotics might be warranted. Or she was given them to prevent the superinfection/secondary infection. This is true of any viral illness, even corona viruses, rhinoviruses and covid 19.