Antiviral Drug Classes and Mechanisms of Action

Antiviral drugs are grouped by the step of the viral replication cycle they block — attachment and entry, genome replication, polyprotein processing, integration, or release. Because viruses borrow host machinery, each class is judged by how selectively it strikes a viral target while sparing the host, the basis of its therapeutic index.

Definition

Antiviral drug classes are categories of agents defined by the viral replication step and molecular target they inhibit — for example viral polymerases, proteases, integrases, entry receptors, or release enzymes — each class sharing a mechanism of action that suppresses viral propagation.

Scope

This topic surveys the principal antiviral mechanisms and the drug classes that exploit them: entry and fusion inhibitors, nucleoside and non-nucleoside polymerase inhibitors, protease inhibitors, integrase inhibitors, and neuraminidase (release) inhibitors. It explains how each class works at the molecular level. It does not provide dosing or prescribing guidance.

Core questions

• Which steps of viral replication are druggable targets?
• How do nucleoside analogues differ from non-nucleoside inhibitors?
• Why do protease and integrase inhibitors work against retroviruses like HIV?
• How do neuraminidase inhibitors act against influenza?
• What determines selective toxicity and the therapeutic index of an antiviral?

Key concepts

• Viral replication cycle as a sequence of drug targets
• Entry and fusion inhibitors
• Nucleoside and nucleotide analogues
• Non-nucleoside polymerase inhibitors
• Viral protease inhibitors
• Integrase strand-transfer inhibitors
• Neuraminidase (release) inhibitors
• Selective toxicity and therapeutic index

Mechanisms

Each class interrupts a distinct stage. Entry and fusion inhibitors block attachment to or fusion with the host cell. Nucleoside and nucleotide analogues are incorporated into the growing viral genome by the viral polymerase, causing chain termination or lethal mutagenesis; non-nucleoside inhibitors bind the polymerase allosterically. Protease inhibitors prevent cleavage of viral polyproteins into functional units, and integrase inhibitors stop retroviral DNA from inserting into host chromatin — both pivotal in HIV therapy, as reviewed by Arts and Hazuda (2012). Neuraminidase inhibitors prevent release of progeny influenza virions, the mechanism of oseltamivir tested by Nicholson et al. (2000). De Clercq and Li (2016) catalogue these classes across five decades of approved agents, and the polymerase-inhibitor remdesivir studied by Beigel et al. (2020) exemplifies the nucleotide-analogue strategy applied to a new virus.

Clinical relevance

Knowing a drug's class predicts its spectrum, its likely resistance pathways, and how it combines with others, which is why mechanism-based classification underlies rational antiviral use. This entry explains how the classes act and how their effect has been demonstrated in trials; it is not a guide to selecting or dosing any specific drug.

History

Antiviral chemotherapy began in the 1960s with early nucleoside analogues and matured through the HIV era, when combination regimens of reverse-transcriptase, protease, and later integrase inhibitors transformed prognosis, as recounted by Arts and Hazuda (2012). De Clercq and Li (2016) trace the broader arc of approved antivirals, and the rapid repurposing of remdesivir for COVID-19 (Beigel et al., 2020) extended the polymerase-inhibitor lineage to an emerging threat.

Key figures

• Erik De Clercq

Seminal works

• declercq-li-2016
• arts-hazuda-2012

Frequently asked questions

How is an antiviral drug class defined?

It is defined by the step of the viral life cycle and the molecular target it blocks, such as the viral polymerase, protease, integrase, or release enzyme, so drugs in a class share a mechanism of action.

Why are there fewer antiviral classes than antibacterial classes?

Viruses replicate using the host cell's own machinery, leaving fewer uniquely viral targets to attack without harming host cells, which limits the number of selectively toxic drug classes.