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[Pharmacology](https://durgical.com/en/pharmacology/) · Class

# Anti-influenza agents

Antivirals against flu that work best when started early. They shorten illness; they do not replace the yearly vaccine.

Updated 2026-11-01

## What they are

Medicines that treat or prevent influenza A and B. They help most when started early, especially in people at high risk of complications (pregnancy, young children, older adults, chronic disease, immunosuppression). They do not replace the annual vaccine, and they do not prevent bacterial complications.

## Mechanism of action

Neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) block the viral enzyme that cuts sialic acid, so new virions stay stuck to the infected cell and to each other and cannot spread. Baloxavir blocks the cap-dependent endonuclease of the viral PA protein, which the virus needs to steal caps from host mRNA and start making its own mRNA. The old adamantanes (amantadine, rimantadine) block the M2 channel, but circulating strains are widely resistant.

Target: Viral neuraminidase; PA cap-dependent endonuclease

## Key points

- Neuraminidase inhibitors prevent the release of new virions from the infected cell.
- Oseltamivir is oral; zanamivir is inhaled and can cause bronchospasm in asthma or COPD.
- Baloxavir is a single oral dose; dairy products and antacids or supplements with calcium, magnesium, iron or zinc reduce its absorption.
- The intranasal live attenuated vaccine may not work if given close to these antivirals; inactivated vaccine can be given at any time.
- Neuropsychiatric events (confusion, abnormal behaviour) have been reported in people with flu, mainly children, with or without these drugs.

## Drugs in this class

- [**Oseltamivir** An oral antiviral for influenza A and B. Started within 2 days of symptoms, it shortens the illness; it can also… Influenza virus neuraminidase](https://durgical.com/en/pharmacology/oseltamivir/)
- [**Zanamivir** An inhaled neuraminidase inhibitor for influenza. It acts directly in the airways but can cause bronchospasm in asthma… Influenza virus neuraminidase](https://durgical.com/en/pharmacology/zanamivir/)
- [**Baloxavir marboxil** A single-dose oral flu antiviral that blocks the virus's «cap-snatching» enzyme. Milk and mineral supplements reduce… Cap-dependent endonuclease of the influenza polymerase (PA subunit)](https://durgical.com/en/pharmacology/baloxavir-marboxil/)

## Others in the class

- Peramivir
- Laninamivir
- Amantadine
- Rimantadine

## Test yourself

Think of the answer, then tap the question to see it.

## What does a neuraminidase inhibitor prevent?

The release of new influenza virions from the surface of the infected cell, so the infection spreads less.

## Which anti-influenza drug is inhaled and needs caution in asthma?

Zanamivir: it can cause serious bronchospasm in people with asthma or chronic lung disease.

## What viral enzyme does baloxavir block?

The cap-dependent endonuclease of the PA subunit of the viral polymerase, which «steals» caps from host mRNA.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Influenza (seasonal)](https://www.who.int/news-room/fact-sheets/detail/influenza-(seasonal)) (World Health Organization, 2025); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 62 (McGraw Hill, 2023); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J05AH) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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