oseltamivir phosphate at a glance
Medicine class
Neuraminidase inhibitor antiviral
Main role
Treatment and selected prevention of influenza A and B
Administration
Taken by mouth, with or without food; food may reduce nausea or vomiting
Important check
Kidney impairment may require an adjusted prescription
What is oseltamivir phosphate used for?
Licensed uses represented by the selected product include:
Treatment of influenza in adults and children, including full-term newborn babies, when typical symptoms occur while influenza is circulating.
Post-exposure prevention in people aged one year and over after contact with a clinically diagnosed case, considered individually.
Exceptional seasonal prevention in people aged one year and over, such as during a pandemic or substantial vaccine-strain mismatch.
Post-exposure prevention in infants under one year during a pandemic influenza outbreak.
How does oseltamivir phosphate work?
Oseltamivir phosphate is converted mainly in the liver to oseltamivir carboxylate. This blocks influenza neuraminidase, an enzyme the virus uses to release new viral particles and spread between cells. It acts against influenza A and B, not unrelated cold or respiratory viruses.
oseltamivir phosphate preparations and strengths
Capsule
Route: Oral
Strengths: 30 mg, 45 mg, 75 mg
How to take oseltamivir phosphate
Use exactly as prescribed. Swallow capsules whole with water; do not chew or break them. They may be taken with or without food, although food can reduce nausea or vomiting.
A commercially manufactured oral suspension is preferred when capsules cannot be swallowed or smaller measured quantities are required.
Do not improvise a liquid preparation unless a pharmacist or the supplied patient leaflet gives product-specific instructions.
Do not stop or alter the prescribed course without advice from the prescriber or pharmacist.
oseltamivir phosphate side effects
Common or expected effects
- Nausea or vomiting
- Headache
- Stomach pain or indigestion
- Vomiting in children; diarrhoea and nappy rash have also been reported in infants
Get urgent medical advice
- Severe allergic reaction or angioedema
- Severe blistering or peeling skin reactions
- Liver inflammation, liver failure or jaundice
- Gastrointestinal bleeding
- Seizures, delirium, hallucinations, severe confusion or abnormal behaviour
oseltamivir phosphate in pregnancy
Influenza can cause more serious complications during pregnancy. Oral oseltamivir is considered the first-line antiviral for most pregnant patients with influenza in UK public-health guidance. Available observational data have not shown an overall increase in fetal malformations, but prescribing should consider individual benefits and uncertainties. A pregnant person who thinks they have influenza should contact a clinician.
oseltamivir phosphate while breastfeeding
Oseltamivir can be used during breastfeeding when clinically indicated and is the preferred antiviral in UK specialist guidance. Only negligible amounts are expected in breast milk. For a full-term healthy infant, monitor as a precaution for vomiting, diarrhoea, irritability or sleep changes; seek specialist advice if the infant is premature or unwell.
oseltamivir phosphate interactions
Clinically significant interactions are generally uncommon, but important examples include:
Probenecid
Increases exposure to the active metabolite, although adjustment is not normally required when renal function is normal.
Methotrexate, chlorpropamide or phenylbutazone
Use caution because competition for renal tubular secretion may be important for medicines with a narrow therapeutic margin.
Live attenuated influenza vaccine
Influenza antivirals may reduce the vaccine's effectiveness, so administration should be coordinated with the prescriber or vaccinator.
Common questions about oseltamivir phosphate
Answers are fully visible for fast scanning and source review.
Is oseltamivir phosphate an antibiotic?
No. It is an antiviral that acts against influenza viruses; it does not treat bacterial infections.
Does oseltamivir phosphate replace a flu vaccination?
No. Its protection is temporary and it does not replace annual influenza vaccination.
Why does kidney function matter with oseltamivir phosphate?
Sources
These sources were used to prepare and review this medicine page.
Prepared and reviewed by the iatroX editorial team.