Everyone knows: viral infections cannot be treated with antibiotics! After all, antibiotics are drugs that kill bacteria. And if you use them to fight viruses, then bacteria develop resistance (resistance) to antibiotics. And this threatens humanity with a catastrophe.
However, this is not the first time that there have been reports that antibiotics can (and even should) be used to treat certain viral infections. MedAboutMe understands what these infections are and what these antibiotics are.
Zika virus and antibiotics: hopes
Almost 75 years ago, the Zika virus was discovered. In 2007, they started talking about him because of the outbreak of Zika fever on the island of Yap, but the virus gained real "popularity" in 2015, when it reached the American continents and began to rapidly spread throughout South and Central America. The virus is tropen, that is, it prefers to infect nerve stem cells, as well as individual types of glial cells - the aggregate of cells surrounding nerve fibers. This tropism of the virus to the stem cells of the nervous system explains why the fetal brain suffers in a pregnant woman infected with the Zika virus.
In a 2017 study, the first reports appeared that certain antibiotics had a therapeutic effect on Zika virus infection. And in December 2020, PNAS magazine published an article by American scientists on the results of the search for drugs against the Zika virus. Using the high-throughput screening method (computer testing of hundreds of thousands of chemicals), they looked for compounds that could negatively affect the functioning of the Zika virus. As a result of the screening of more than 138 thousand substances, the number of candidates for the drug included, for example, protease inhibitors of the Zika virus. But antibiotics of the tetracycline series turned out to be much more powerful inhibitors of viral infection. The strongest of them - metacyclin - reduced the concentration of the virus in the brain tissues and reduced the severity of viral damage to the nervous system in experimental mice.
Among the potential drugs for Zika fever was novobiocin, an antibacterial drug that has not reached the market. It effectively prevented the infection with the Zika virus of cells specially prepared for the experiment in mice. However, among the side effects of novobiocin were problems with the gastrointestinal tract, skin rashes, leukopenia, inhibition of bilirubin metabolism and the resulting jaundice in infants.
Antibiotics as prevention of viral infection: a disappointment
In 2018, the journal Cell Reports published the results of studies on prophylactic antibiotics to protect against certain viral infections. It was about the viruses of dengue, West Nile and the Zika virus, that is, about the representatives of the flavivirus family.
Previously, it was shown that antibiotics, which were administered to mice infected with these viruses, in some cases reduced the destructive effect of the infection. Scientists have suggested that this is an indirect effect of antibiotics on the human microbiome. However, for viruses from other families, the introduction of antibiotics, on the contrary, worsened the situation.
The researchers observed three groups of mice: the first received an oral cocktail of antibiotics from different groups (aminoglycosides, tricyclic glycopeptides, penicillins) 2 weeks before infection with the West Nile virus, the second - 2 weeks after infection, the third - did not receive antibiotics at all. Of the mice that received antibiotics in one way or another, only one individual survived, of the animals untreated with antibiotics, about 80%. The experiments were repeated with Zika and dengue viruses - prophylaxis and antibiotic treatment invariably worsened the result.
The study found that antibiotic treatment led to a decrease in the concentration of immune cell precursors, in particular CD8 + T-lymphocytes, which are involved in recognizing and destroying virus-infected body cells. That is, there is a possibility that antibiotics affected immunity by affecting not only the human microflora, but also the immune system directly. The mechanism of this action is not yet known, so it is too early to draw final conclusions.
One thing is clear: antibiotics should not be taken as a preventive measure to protect against viruses.
Why look for a cure for viruses among antibiotics?
Why do scientists even undertake to look for a remedy for the virus among antibiotics?
First of all, because when infected with a virus, there is a risk of superinfection - the addition of bacterial infection against the background of a weakened immune system of the body. In addition, some antibiotics have the ability to enhance the effects of other drugs.
And antibiotics are very well studied drugs. There is no need to conduct phase I clinical trials - their safety for a healthy adult has already been proven, and this significantly reduces the financial and time costs of research in general.
Also, many antibiotics from the same group of tetracyclines are able to overcome the blood-brain barrier, so they can be used as a medicine for lesions of the central nervous system and brain tissues.
Finally, they pass through the placental barrier in pregnant women, which means they can be used to treat fetal infections, which is especially important in the case of Zika. Therefore, by the way, it is not recommended to use antibiotics from this group after the first trimester of pregnancy, as they can change the color of the fetus's teeth. And the Zika virus, although it can cause congenital malformations at any time, is most dangerous when infected in the first 3 months of pregnancy. And tetracyclines of the latest generations no longer have pronounced teratogenic effects (that is, dangerous to the fetus).
Antibiotics for COVID-19
Attempts to use antibiotics in the treatment of viral diseases continue. Last year, during the COVID-19 pandemic, early studies by Chinese and French scientists flashed the idea of prescribing hydroxychloroquine in combination with the antibiotic azithromycin. In a small sample of patients, it was argued that azithromycin enhances the antiviral effect of hydroxychloroquine.
Indeed, this antibiotic has an anti-inflammatory effect and suppresses the immune system's response to infection with SARS-CoV-2 - as we recall, one of the most severe complications of COVID-19 is the pathological reaction of the immune system, manifested in the form of a cytokine storm. And finally, azithromycin was supposed to play a preventive role, preventing bacterial infection at a time when the body is weakened by the fight against COVID-19.
However, later it was shown that this combination has a negative effect on the heart rate, significantly increasing the risk of heart failure and premature death of the patient. And later, the results of larger studies arrived, which proved the low efficacy of hydroxychloroquine, combined with a high risk of side effects. Separately prescribed azithromycin, which was supposed to protect the weakened patient, at the same time cleared the field for fungal infections.
Therefore, today it is not recommended to treat COVID-19 with hydroxychloroquine and without a real need to take azithromycin (and other antibiotics) during this illness.
So antibiotics against the virus are possible. But only for certain diseases and only under strict medical supervision. For example, in the case of the Zika virus, we are talking about the concept of "lesser evil": the benefits of taking tetracyclines during pregnancy may outweigh the potential risks. Or in the absence of other methods of treatment or the development of neurological complications, antibiotics can have a therapeutic effect to prevent the development of Guillain-Barré syndrome, encephalitis and myelitis in adults - taking into account the possible negative consequences, of course.