Oseltamivir
Oseltamivir is an oral neuraminidase inhibitor used in adults and children for the treatment and prophylaxis of influenza A and B. It is most effective when started early in symptomatic infection and is part of pandemic preparedness stockpiles.
- Chemical formula
- C16H28N2O4
- CAS number
- 196618-13-0
- ATC code
- J05AH02
- Molecular weight
- 312.40 g/mol
- Drug class
- Neuraminidase inhibitor
- Also known as
- GS-4104, Oseltamivir
What is it?
Oseltamivir is a neuraminidase inhibitor approved for clinical use in 1999, supplied as oral capsules and oral suspension. Oseltamivir is dispensed only on prescription in most jurisdictions and is part of the World Health Organization List of Essential Medicines. It has been stockpiled by many governments for pandemic preparedness, although the magnitude of clinical benefit in routine seasonal influenza has been debated in evidence reviews.
Mechanism of action
Oseltamivir is a prodrug rapidly hydrolysed by hepatic esterases to the active metabolite oseltamivir carboxylate, which selectively inhibits the neuraminidase enzyme on the surface of influenza A and B viruses. Neuraminidase is required for the release of newly formed virions from infected cells and for spread of virus through the respiratory mucus, so its inhibition reduces viral replication and clinical illness when treatment is started early.
Pharmacokinetics
Oral oseltamivir is well absorbed, with bioavailability of approximately 80% as the active carboxylate metabolite. Plasma protein binding is low. Oseltamivir carboxylate is excreted unchanged in urine via tubular secretion, with a plasma half-life of approximately 6 to 10 hours. Renal impairment requires dose reduction. Food does not significantly affect absorption. Pharmacokinetics in children are weight-adjusted.
Indications
Oseltamivir is approved in adults and children for the treatment of acute uncomplicated influenza A and B when started within 48 hours of symptom onset, and for post-exposure prophylaxis of influenza A and B in patients aged 1 year and older. According to international guidelines, treatment is recommended for patients at high risk of complications, those requiring hospitalisation and severe progressive disease. Routine treatment of low-risk patients with mild influenza is more controversial.
Safety profile
Common adverse effects include nausea and vomiting, particularly when taken without food. Headache and rash are also reported. Neuropsychiatric events, including delirium and abnormal behaviour, have been reported in postmarketing surveillance, particularly in children and adolescents in Japan, although a causal relationship with oseltamivir versus the underlying influenza is debated. According to the prescribing information, dose adjustment is required in renal impairment.
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Frequently asked questions
When is oseltamivir most effective? ▾
Oseltamivir is most effective when started within 48 hours of influenza symptom onset, and ideally within 24 hours. Earlier treatment provides greater reductions in symptom duration. According to international guidelines, treatment should still be considered after 48 hours in patients hospitalised with severe disease or at high risk of complications, where the benefits may persist beyond the early window.
Can oseltamivir prevent influenza after exposure? ▾
Yes. Post-exposure prophylaxis with oseltamivir is approved for patients aged 1 year and older after close contact with a confirmed or suspected case of influenza, particularly during outbreaks in households or institutional settings. According to the prescribing information, prophylaxis is typically given for 7-10 days following exposure. Vaccination remains the primary preventive strategy and should not be replaced by antiviral prophylaxis.
Why must the dose be reduced in kidney disease? ▾
Oseltamivir carboxylate is excreted unchanged in urine, so renal impairment substantially increases plasma concentrations and the risk of adverse effects. According to the prescribing information, the dose is reduced based on creatinine clearance, with specific recommendations for patients on haemodialysis and peritoneal dialysis. Renal function should be assessed before treatment, particularly in older adults.
Are neuropsychiatric events a real concern? ▾
Reports of neuropsychiatric events, including delirium and self-injury, were predominantly received from Japan in children and adolescents. Causality with oseltamivir versus the underlying influenza is debated, as similar events occur in untreated influenza. According to regulatory communications, patients (particularly children) should be observed for unusual behaviour during treatment, but oseltamivir is not contraindicated when clinically indicated.
What are the main contraindications for oseltamivir? ▾
Oseltamivir is contraindicated in known hypersensitivity to oseltamivir or its excipients. Caution is required in renal impairment (with mandatory dose adjustment), in younger children (where dosing is weight-based), in pregnancy and breastfeeding (where benefits typically outweigh risks), and in patients with previous neuropsychiatric reactions. According to the prescribing information, the medical history must be reviewed by a clinician before any prescription.
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