Antiviral drugs

Content

Introduction

Introduction

Antivirals are medicines that are used to fight infections caused by viruses. They belong to the broadest category of drugs, defined antimicrobials, which also includes antibiotics, active against diseases of bacterial origin, antifungals (active against diseases due to fungi), and pesticides (active against protozoal diseases and parasites).

Some antiviral medicines are specifically active against certain viruses or families of viruses, such as influenza, herpes, HIV or hepatitis B (HBV) or C (HCV) viruses, while others are broad range, in other words, they can be effective against a variety of viruses.

In general, antiviral drugs work by blocking a vital phase in the multiplication cycle of the virus, thus preventing its development and spread. It is important to underline that viruses are not microorganisms with autonomous life but they are gods obligate cell parasites, needing, in order to reproduce, to use the survival mechanisms of the cell that hosts them.

For more information on the active ingredients named in the contribution or in any case belonging to this class of drugs, you can visit the website of the Italian Medicines Agency (AIFA) by clicking HERE.To search for a drug using the trade name and not the active ingredient you can click HERE. Inside the site you can find all the package leaflets of the drugs and also some additional information. If "revoked" is written next to the name of the drug, the drug is no longer on the market.

Viral diseases and prevention

Viral diseases and prevention

Viral infections are widespread. Some can cause mild ailments such as the common cold; others can cause serious diseases such as acquired immunodeficiency syndrome (AIDS) or major forms of hepatitis. In healthy individuals, that is, those who have the body's defense system (immune system) functioning, most viral infections resolve spontaneously without treatment. Common examples are colds and viral gastroenteritis caused by rotavirus. However, some viral infections lurk in some cells of the body and cause an infection that lasts over time (chronic) and can seriously endanger human health. This is the case of hepatitis B virus infection. or C and HIV.

The first line of defense against viral diseases is prevention, with its most effective form being vaccination. However, a vaccine has not yet been discovered for some diseases. Therefore, it is important to be able to have useful medicines to counter the advancement of viral infections once they have developed in the body causing a certain disease.

Clinical use of antivirals

Clinical use of antivirals

There are several types of antiviral drugs. Some of them are active on a large variety of viruses, others only on certain types of viruses, sometimes even unrelated, and finally others are active only on specific viruses. Different viruses, in fact, use different mechanisms to penetrate inside cells, duplicate their genetic makeup, produce new viral particles and then infect other cells. All these phases represent potential targets for antiviral drugs.

In general, research is progressing towards the definition of drugs with an increasingly specific action, aimed at recognizing and inhibiting specific viral proteins. These new generation drugs, often designed with computerized systems, are generally more effective and less toxic than the less recent and generic drugs.

Interferons are among the first generation antivirals with a broad spectrum of action. These are substances produced by the body, which represent a natural defense measure that is activated when one is struck by a viral infection. The mechanisms of the antiviral action of interferon are both direct, interfering (hence the name "interferon ") With viral synthesis in infected cells, both indirectly, by stimulating the immune system. For many viral diseases they represented in the past the only active drugs but today they have been replaced for many viral diseases, especially hepatitis C, by drugs more specific and more active.

Drugs that interfere with the replication of viral nucleic acids (DNA and RNA) generally have a similar structure to the nucleosides that make up the chains of nucleic acids. For this reason they are called nucleoside analogues and have an antiviral spectrum of intermediate amplitude. This category includes ribavirin (used above all in the past in "type C viral hepatitis in combination with interferon), drugs aimed at the viral family of herpes (herpes simplex or labialis, varicella zoster and herpes zoster, cytomegalovirus), and some drugs active against the hepatitis B virus and HIV.

Other drugs inhibit virus-specific enzymes and are therefore highly selective for a particular virus. For example, some specific flu drugs inhibit neuraminidase, a molecule, present on the surface of the influenza virus, which plays a fundamental role so that the new viral particles formed inside an infected cell are released and infect other cells. Other drugs active against HIV or the hepatitis C viruses act by inhibiting specific enzymes of these viruses. Numerous drugs are now available against hepatitis C viruses (direct acting antivirals, targeting non-structural HCV proteins) and against HIV (see below) and their introduction into the clinic has made it possible to significantly modify the natural history of these diseases.

Clinical research has also made it clear that for some virus infections, such as HIV and hepatitis B and C virus infections, combination antiviral therapy schemes are required to effectively and sustainably inhibit viral replication. For example, for HIV (the agent that causes AIDS or acquired immunodeficiency syndrome), current therapy is based on the simultaneous blocking of multiple replicative functions of the virus, such as: reverse transcription,that is, the ability to synthesize a DNA molecule starting from viral RNA, theintegration, that is, the ability of the virus to insert this DNA molecule into the genome of the host cell, and the formation of viral proteins. All these functions are performed by virus-specific enzymes (reverse transcriptase, integrase, protease), for which specific inhibitors are now available capable of suppressing virus replication, blocking the production and assembly of new viral particles.

The search for new and increasingly effective drugs is crucial for finding remedies against viral infections, often very serious for human health, for which valid vaccines do not yet exist. A big problem that scientists face is that of the ability of viruses to change and become resistant to drugs. Therapeutic strategies are being studied that are increasingly effective in preventing the development of drug resistance and new different therapeutic targets are being identified for applying second-line antiviral therapies that maintain antiviral activity even on viral strains that have developed drug resistance.

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