oseltamivir
Oseltamivir (Tamiflu) is an oral antiviral used to treat and prevent influenza A and B in adults, children, and neonates. It blocks the flu virus's neuraminidase enzyme, preventing newly formed virus particles from escaping infected cells and spreading to others. It works best when started within 48 hours of symptom onset and is not a substitute for influenza vaccination.
This page is based on the European Medicines Agency assessment report for Tamiflu and DailyMed labeling for oseltamivir phosphate capsules, cross-checked with MedlinePlus and the National Cancer Institute drug dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
Flu viruses are like tiny balloons that bud off from an infected cell, still tethered to the cell surface by sticky sugar threads. Oseltamivir blocks the virus's scissors (neuraminidase) that would normally cut those threads. The new viruses stay stuck to the cell and cannot spread to infect other cells, so the infection runs out of steam.
In simple terms
Oseltamivir is an antiviral medicine that treats and prevents influenza (the flu). After the flu virus infects a cell and makes copies of itself, the new virus particles need to break free from the cell surface to spread to other cells. They do this using an enzyme called neuraminidase, which acts like a pair of scissors cutting sugar chains that hold the viruses in place. Oseltamivir blocks these scissors, so the new viruses stay stuck and cannot spread. It works best when started within 2 days of flu symptoms and is not a substitute for the annual flu vaccine.
In depth
Oseltamivir phosphate is an orally administered prodrug that is hydrolysed to the active metabolite oseltamivir carboxylate. Oseltamivir carboxylate is a potent, selective inhibitor of influenza A and B viral neuraminidase, the enzyme that cleaves terminal sialic acid residues from glycoproteins on the host cell surface and on viral envelopes. By blocking neuraminidase, oseltamivir prevents the release of progeny virions from infected cells and limits the spread of infection within the respiratory tract. It is indicated for treatment of acute uncomplicated influenza in patients aged 2 weeks and older who have been symptomatic for no more than 48 hours, and for prophylaxis of influenza in patients aged 1 year and older.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
Flu viruses are like tiny balloons that bud off from an infected cell, still tethered to the cell surface by sticky sugar threads.
- After the flu virus infects a cell and makes copies of itself, the new virus particles need to break free from the cell surface to spread to other cells.
- They do this using an enzyme called neuraminidase, which acts like a pair of scissors cutting sugar chains that hold the viruses in place.
- The new viruses stay stuck to the cell and cannot spread to infect other cells, so the infection runs out of steam.
- It works best when started within 2 days of flu symptoms and is not a substitute for the annual flu vaccine.
Target: Influenza neuraminidase
Oseltamivir's active metabolite inhibits the influenza viral neuraminidase enzyme, preventing cleavage of sialic acid residues from host-cell glycoproteins and thereby blocking release of newly formed virions from infected cells.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in European Union
EMA- Treatment of influenza in adults and children including full-term neonates who present with symptoms typical of influenza, when influenza virus is circulating in the community
- Post-exposure prevention of influenza in individuals 1 year of age or older
- Seasonal prevention of influenza in individuals 1 year of age or older in exceptional situations
- Post-exposure prevention of influenza in infants less than 1 year of age during a pandemic influenza outbreak
Approved uses in United States
DailyMed- Treatment of acute uncomplicated illness due to influenza A and B in patients 2 weeks of age and older who have been symptomatic for no more than 48 hours
- Prophylaxis of influenza A and B in patients 1 year and older
Approved uses in United States
MedlinePlus- Treatment of influenza in adults, children, and infants older than 2 weeks of age
- Prevention of influenza in adults and children older than 1 year of age after exposure or during outbreaks
Official sources
The statements on this page trace back to these records.
- Tamiflu (oseltamivir) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- DailyMed: oseltamivir phosphate capsules label
DailyMed, U.S. National Library of Medicine
- MedlinePlus: oseltamivir
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: oseltamivir phosphate
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.