Antivirals: What Are They and How Do They Work?
There is a large number of pathologies produced by viruses. This results in the need to create drugs to combat them. This is how antivirals arise.
The human body is capable of eliminating various infections caused by viruses on its own. However, there are variants and types of these particles that have defense mechanisms to evade the immune system.
One of the defense mechanisms is mimicry, where they camouflage themselves within cell structures, eluding white blood cells. This is one of the methods applied by the human immunodeficiency virus (HIV), which makes it difficult to treat.
What are antivirals?
In general terms, antivirals are drugs created with the purpose of inhibiting the replication of viruses within the body. Viruses are intracellular, that is, they need to invade the cells of a host to multiply, which makes it difficult to approach them.
It’s important to note that these drugs aren’t capable of eliminating the causative agent, as antibiotics do with bacteria. In this sense, studies have shown that if intakes or applications are suspended, the disease could reappear.
Although antivirals don’t represent a complete cure, they are capable of reducing symptoms. This happens because the drugs prevent the amount of virus in the body from increasing, reducing the severity of the clinical picture.
These drugs used to have various side effects in patients due to their toxicity, however progress has been made and they are becoming safer. Among the diseases that can be treated with antivirals, the following stand out:
- Herpes
- Hepatitis B and C
- Cytomegalovirus
- Respiratory syncytial virus
- Flu
Mechanism of action of antivirals
Viruses perform various cycles within the cells of the human body. The final result of all these reactions will be the replication of the viral DNA or RNA, which will cause an increase in the load and a worsening of the infection.
The most effective antivirals inhibit certain reactions that allow viral multiplication or inhibit its replication. In this sense, these drugs have different mechanisms of action.
Preventing entry into the cell
All viruses need to enter the cell in order to complete their cycle, so they must first adhere to the plasma membrane and then penetrate it. In this sense, some drugs are capable of preventing either of these two processes by inducing small changes in the cell.
Among the most notable modifications are the creation of false receptors or the synthesis of antibodies against viral receptors. In this way, the virus won’t be able to enter and will be eliminated by the immune system.
Locking cover loss
Viruses must lose a membrane called a capsid upon entering the cell for replication to occur. Certain antivirals prevent its dissolution, so they won’t be able to release their genetic material.
The drugs can inhibit the calcium channels that allow the release of DNA and RNA. In addition, they can also act as membrane stabilizers, preventing their destruction.
Inhibition of genome transcription
The genome is the part of the virus that contains the genetic information (DNA or RNA) and allows its multiplication. The objective of the viruses is to achieve transcription, that is, the replication of this material to reproduce.
This transcription process is carried out through various enzymes, which can be inactivated by some drugs. Some of the enzymes involved in this process are viral DNA polymerase, RNA polymerase, and reverse transcriptase.
Alteration of viral proteins
RNA viruses create a compound called messenger RNA, which will be able to synthesize viral proteins using the structure of the affected cell. All these proteins are necessary for the virus to continue its cycle. Some antivirals have the ability to destroy or disable these proteins through their interaction with them.
Release prevention
Once there’s a new viral load, it’s released into the bloodstream and is capable of infecting another cell. This release can be prevented, so the immune system will be able to destroy the affected cell and the viruses found in it.
Classification of antivirals
To facilitate their study, researchers have divided several of the existing antivirals into 3 broad categories, depending on the diseases they can treat. In this sense, the following stand out among the main groups.
Herpetic virus drugs
Herpes simplex virus infection is caused by two types of DNA viruses: HSV-1 and HSV-2. In this sense, the first drug approved to treat the disease was vidarabine, however it’s no longer available. Currently, the treatment of choice is acyclovir.
Acyclovir is a drug that blocks the synthesis of viral DNA and its intravenous administration has few side effects. Several studies show that the duration of oral lesions was reduced when it was administered.
Other antivirals that are administered for herpes virus infections are the following:
- Cidofovir
- Doconasol
- Fanciclovir
- Penciclovir
Influenza drugs
All viruses that cause flu or influenza are RNA viruses, so other drugs than those mentioned above are used. It’s important to mention that the drugs used in these cases are also used to treat respiratory syncytial virus infections.
The most commonly used in these cases are amantadine and rimantadine. Both are highly reactive with the influenza A virus, although studies show that rimantadine is up to 10 times more effective. They inhibit early replication of the virus by preventing capsule loss.
Drugs used to treat hepatitis
Finally, the last group of drugs is made up of those used to treat hepatitis B and C. In this case, the drug of choice is adenofovir, which will prevent viral DNA transcription by inhibiting the enzymes involved in the process.
In addition, interferons, which are compounds that function as intercellular communicators, can also be used. They will make the cells synthesize proteins that increase the viral resistance of the same.
General considerations about antivirals
Antivirals are medicines used in infections caused by viruses that the immune system cannot fight on its own. Its main function is to inhibit the multiplication of the infectious agent and not the elimination. In this sense, the virus can remain latent within the body.
Currently, these compounds have few side effects, so their administration is safe in most cases. However, their consumption should be carried out under strict medical supervision.
We haven’t included antiretrovirals in the article, as they constitute a category in themselves. Some are used as a priority for the treatment of HIV infection and the acquired immunodeficiency syndrome (AIDS).
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