Humans are certainly not the only living creatures to be living on earth. It is impossible for us humans to be living alone as many other organisms do interact with humans in many ways. Microorganisms such as viruses can cause bad health effects to humans. There are antivirals that can help treat diseases caused by viruses. In this DoctorOnCall’s article, we will learn about antiviral resistance which has caused issues in the medicine world.
Viruses is a microbe made up of nucleic acid (DNA/RNA). The virus can’t survive on its own because it needs cells in humans before making copies of itself. Viruses are capable of causing viral infections because they control the cell they infect and produce more viruses. That’s going to kill the normal cells in your body. Viruses can also cause people to become infected, by losing control of the infected cells and becoming cancerous or changing how they function. In general, virus make contact with cells and invade cells, releasing the virus’s genome into the cell to replicate more viruses. The replication is made possible by the viral protein produced.
Antiviral drugs are a class of medicine used in treating viral infections. Antivirals inhibit virus attachment to normal cells and prevent the virus from copying genetic material and making more viruses. Among the common antivirals used is in treating hepatitis B, hepatitis C, HIV and COVID-19. Only a small number of viruses are treated with antivirals. Antivirals are more difficult to develop since they usually damage the host cells which means more health risk for humans. It’s also got less protein and enzymes, which makes the development of new antivirals difficult even when it is needed. In addition, even among the same class, viruses have many different sequences and structures, so antivirals can only be used against one type at a time. Even though drugs for herpes, influenza and some new antiviral for hepatitis C and HIV are available, there are still no effective antiviral drugs available for the many viral infections.
Now, what is antiviral resistance? Antiviral resistance occurs when a virus does not respond to an antiviral. This will lead to selection of virus strains to be resistant towards antivirals. While it is true that the increased number of viral infections that impair human health can be treated using antivirals, it typically targets the mechanism of viral replication. No virus replication can be achieved with proper treatment and the virus is impaired sufficiently. Certainly, this is the ideal or expected outcome when using antivirals. However, when treatment is ineffective and some viruses are still able to replicate, it may lead to the resistance that is not what health professionals hope for. The resistance will be worst when it occurs in large population size and high rate of mutation characterising many viruses.
What causes antiviral resistance? The main cause for this event is the prolonged antiviral drug exposure and the ongoing viral replication due to immunosuppression. This will then lead to occurrence of persistent or increased viremia or disease despite therapy having been given. The downside of the antiviral resistance ranges from toxicity inherent from the use of second-line antivirals to severe disease. In some cases, it may even lead to death resulting from the progressive viral infection as no effective alternative treatments are available.
To better understand how problematic antiviral resistance can be, let’s take an example of antiviral in flu viruses. Flu viruses are constantly changing and these changes do make certain antivirals become resistant which means it does not work against the viruses. Antiviral for flu works by targeting specific location or site within the flu virus. When the flu virus develops changes of the site where the antiviral drugs target, the virus may show low response or no response towards the antiviral drug. Antiviral drugs known as M2 inhibitors such as amantadine and rimantadine, also called the adamantane, were active against flu A viruses. However, the adamantane antiviral drugs are not recommended to treat flu for many years due to the antiviral resistance to this class of antivirals among circulating flu A virus. Even so, recommendations could change if there were future re-emergence of specific virus strains that may respond to certain antivirals that are not recommended now.
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In essence, antiviral drugs are drugs that are used to treat viral infection. Developing antivirals is difficult when compared to antibiotics. Thus, it is best to use antivirals as directed by doctors to avoid antiviral resistance. Antivirals are also easier to become resistant due to difficulty in targeting the virus and because of the virus nature to always have changes in their structure. Antivirals need to be used wisely as it is difficult to develop an alternative and because the cost for the antiviral itself is very costly. It is important to differentiate antibiotics and antivirals despite both being used to treat infection.