Antiviral drugs

Basic classification principles

Modern pharmacology relies on grouping antiviral agents based on their chemical structure and mechanism of action. Globally, all drugs are divided into four major categories:

1. Chemotherapeutic drugs are synthetic molecules for etiotropic treatment that precisely target the pathogen.
2. Interferons are endogenous human body proteins with natural antiviral activity.
3. Interferon inducers are specific substances that stimulate the active production of the patient's own interferons.
4. Immunomodulators are agents designed to correct and restore the immune response.

The main task of synthetic chemotherapeutic drugs is to selectively interrupt virion reproduction without significant damage to the healthy tissues of the host organism.

Targets and sites of action

The viral life cycle consists of several sequential stages. Chemical classes of drugs are tied to specific stages that they are capable of blocking:

• Deproteinization (genome uncoating): the process is disrupted by adamantane derivatives.
• Synthesis of 'early' viral proteins: blocked by guanidine.
• Nucleic acid synthesis: genome replication is effectively halted by nucleoside analogues.
• Synthesis of 'late' viral proteins: inhibited by peptide derivatives.
• Assembly of new virions: a target for the action of thiosemicarbazone derivatives.

Abnormal nucleosides: the basis of therapy

This is the most extensive group of agents that disrupt nucleic acid synthesis. By incorporating into the chain, they make further replication impossible.

• Azidothymidine (AZT): a baseline drug for the treatment of HIV infection (AIDS).
• Acyclovir, vidarabine, idoxuridine: effective against herpes simplex viruses (types 1 and 2) and Varicella Zoster.
• Ganciclovir and cytarabine: used for cytomegalovirus infection (ganciclovir also works against herpes type 1).
• Ribavirin: has a broad spectrum, active against hepatitis C pathogens, Lassa fever, and respiratory syncytial virus.
• Trifluridine: used in ophthalmology for keratitis of adenoviral and herpetic etiology.

Specific chemical classes

Depending on indications, other structural groups are used in clinical practice:

• Adamantane derivatives. Target respiratory viruses. Amantadine and rimantadine are effective against influenza A; adapromine covers influenza types A and B; deitiforin has a complex action (influenza A, parainfluenza, RSV infection). An exception is tromantadine, which is used for herpes.
• Synthetic amino acids. Amben and aminocaproic acid are prescribed for influenza, ARVI, parainfluenza, and RSV infection.
• Pyrophosphate analogues. Foscarnet is used for severe systemic lesions: cytomegaly, hepatitis B, HIV, and herpes (types 1 and 6).
• Thiosemicarbazone derivatives. Methisazone and marboran are historically important drugs used to combat smallpox.
• Virucidal drugs. Topical agents (ointments, drops) that work against extracellular virions. Oxoline, tebrofen, and flurenal rescue in local forms of herpes, rhinitis, and viral keratitis.

Challenges of modern chemotherapy

Despite the colossal production volumes of antimicrobial agents, the physician faces two main problems. The first is the emergence of resistant strains of viruses that rapidly adapt to therapy and reduce treatment efficacy.

The second problem is the shortage of etiotropic drugs. While having a powerful base for therapy of HIV, hepatitis, and herpes, humanity still lacks reliable specific molecules for the treatment of a number of enteroviral infections and dangerous viral encephalitides.

Class and exam questions

What else to study on this topic

• The molecular mechanism of abnormal nucleoside incorporation into the viral genome
• Principles of action of endogenous interferons and inducers of their synthesis
• The role of immunomodulators in the complex therapy of viral diseases
• Causes of viral resistance development to chemotherapeutic drugs
• Pharmacodynamics and specific features of topical virucidal agents' application

Other topics in the section "Chemotherapeutic Antimicrobial Drugs"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.