Antiviral (Neuraminidase Inhibitor) Pregnancy: A large amount of data on exposure during pregnancy (more than 1000 exposed outcomes during the first trimester) indicates no malformative nor feto/neonatal toxicity, although in one observational study results for major congenital heart defects diagnosed within 12 months of birth were not conclusive (1.76% after first-trimester exposure vs 1.01% in unexposed pregnancies; odds ratio 1.75, 95% CI 0.51 to 5.98) and the clinical significance is unclear. Animal studies do not indicate reproductive toxicity. Use may be considered during pregnancy if necessary after considering the available safety and benefit information and the pathogenicity of the circulating influenza virus strain. Breast-feeding: oseltamivir and its active metabolite are detected in breast milk at low levels which would result in a subtherapeutic dose to the infant; administration may be considered where there are clear potential benefits.

Oseltamivir

Brand names: Tamiflu

Oseltamivir is an oral antiviral used in children for the treatment and post-exposure prophylaxis of influenza A and B. This page covers its use in the paediatric population.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: Treatment of influenza: 75 mg oseltamivir twice daily for 5 days (adults and adolescents 13 to 17 years of age)

Route: Oral - patients unable to swallow capsules may receive appropriate doses of commercially manufactured oseltamivir powder for oral suspension (6 mg/ml)

Frequency: Twice daily for 5 days for treatment; 75 mg once daily for 10 days for post-exposure prevention; 75 mg once daily for up to 6 weeks for prevention during a community influenza epidemic

A 75 mg dose can be administered as either one 75 mg capsule or one 30 mg capsule plus one 45 mg capsule. Treatment should be initiated as soon as possible within the first two days of onset of symptoms of influenza; post-exposure prophylaxis should begin as soon as possible within two days of exposure to an infected individual. IMMUNOCOMPROMISED PATIENTS: the recommended treatment duration is 10 days (no dose adjustment is necessary), and seasonal prophylaxis of up to 12 weeks has been evaluated. ELDERLY: no dose adjustment is required unless there is evidence of moderate or severe renal impairment. HEPATIC IMPAIRMENT: no dose adjustment is required for treatment or prevention; no studies have been carried out in paediatric patients with hepatic disorder. PAEDIATRIC WEIGHT-BAND DOSING (children 1 to 12 years, fixed doses by weight band rather than per kg) - TREATMENT for 5 days (10 days if immunocompromised): 10 kg to 15 kg, 30 mg twice daily; over 15 kg to 23 kg, 45 mg twice daily; over 23 kg to 40 kg, 60 mg twice daily; over 40 kg, 75 mg twice daily. POST-EXPOSURE PREVENTION for 10 days: the same weight bands at 30 mg, 45 mg, 60 mg and 75 mg ONCE daily respectively. Prevention during an influenza epidemic in the community has not been studied in children below 12 years of age, nor in children 0-12 months of age. See paedDose for the per-kg infant regimen. Verify all under-18 dosing against a children's formulary.

Paediatric dose

Dose: 3 mg/kg

Route: Oral

Frequency: Twice daily for 5 days (10 days in immunocompromised infants) for treatment of influenza

Max: No per-kg cap is stated for infants 0-12 months; the SPC's worked table runs to 10 kg (30 mg twice daily) and states that for all patients under the age of 1 year, 3 mg/kg should be used to determine dose regardless of the weight of the patient

THIS 3 mg/kg PER DOSE REGIMEN IS FOR INFANTS 0-12 MONTHS OF AGE ONLY. Exact SPC wording (§4.2, Infants 0-12 months of age): 'The recommended treatment dose for infants 0 - 12 months of age is 3 mg/kg twice daily.' Worked examples given: 3 kg = 9 mg twice daily; 5 kg = 15 mg twice daily; 7 kg = 21 mg twice daily; 10 kg = 30 mg twice daily. POST-EXPOSURE PREVENTION in infants 0-12 months during a pandemic influenza outbreak: 3 mg/kg ONCE daily for 10 days (half the daily treatment dose). This dosing recommendation is NOT intended for premature infants, i.e. those with a post-conceptual age less than 36 weeks - insufficient data are available and different dosing may be required due to the immaturity of physiological functions. Children aged 1 to 12 years are dosed by fixed weight band, NOT per kg - see adultDose notes for those bands. There is insufficient clinical data in infants and children 12 years of age and younger with renal impairment to make any dosing recommendation. Verify all under-18 dosing against a children's formulary.

Dose adjustments

Renal

Dose adjustment is recommended for adults and adolescents (13 to 17 years) with moderate or severe renal impairment. TREATMENT: creatinine clearance over 60 ml/min, 75 mg twice daily; over 30 to 60 ml/min, 30 mg twice daily; over 10 to 30 ml/min, 30 mg once daily; 10 ml/min or less, not recommended (no data available); haemodialysis patients, 30 mg after each haemodialysis session; peritoneal dialysis patients, 30 mg single dose. PREVENTION: creatinine clearance over 60 ml/min, 75 mg once daily; over 30 to 60 ml/min, 30 mg once daily; over 10 to 30 ml/min, 30 mg every second day; 10 ml/min or less, not recommended (no data available); haemodialysis patients, 30 mg after every second haemodialysis session; peritoneal dialysis patients, 30 mg once weekly. There is insufficient clinical data available in infants and children (12 years of age and younger) with renal impairment to be able to make any dosing recommendation.

Dose auto-extracted from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Paediatric weight-based calculator

Patient weight (kg)

Verify in a children's formulary

Contraindications

Hypersensitivity to the active substance or to any of the excipients

Side effects

Nausea and vomiting - the most commonly reported reactions in adult/adolescent treatment studies; the majority reported on a single occasion on the first or second treatment day and resolving spontaneously within 1-2 days
Nausea - the most commonly reported reaction in adult/adolescent prevention studies
Vomiting - the most commonly reported reaction in children
Headache (reported as a most common reaction in the US label for both treatment and prophylaxis studies)
Rarely reported since marketing: anaphylactic and anaphylactoid reactions, hepatic disorders (fulminant hepatitis, hepatic function disorder and jaundice), angioneurotic oedema, Stevens-Johnson syndrome and toxic epidermal necrolysis, gastrointestinal bleeding, and neuropsychiatric disorders

Interactions

Live attenuated influenza vaccine (LAIV), intranasal - avoid administration of LAIV within 2 weeks before or 48 hours after oseltamivir, unless medically indicated (US label §7.1)
Inactivated influenza vaccine can be administered at any time relative to oseltamivir use (US label §7.1)
No dose adjustments are needed for either drug when oseltamivir is co-administered with amoxicillin, paracetamol (acetaminophen), aspirin, cimetidine, antacids (magnesium and aluminium hydroxides and calcium carbonates), rimantadine, amantadine or warfarin (US label §7.2)
Interactions are taken from the US prescribing information because the fetched eMC bundle contains no §4.5 section - verify against the full UK SPC §4.5

Clinical monograph

How it works

It is a prodrug converted to oseltamivir carboxylate, which inhibits the influenza neuraminidase enzyme, preventing release of new viral particles from infected cells and limiting spread.

Prescribing in practice

The most important paediatric point is that treatment is most effective when started promptly after symptom onset, and it is generally reserved for at-risk children or during recognised influenza circulation as advised by national guidance.
Dose is weight- and age-based and requires adjustment in renal impairment; doses should be confirmed against a children's formulary, and a suspension is available for young children.
Nausea and vomiting are common, and neuropsychiatric events such as confusion or abnormal behaviour have been reported, so children should be observed for unusual behaviour.

Monitoring

Monitor for clinical response, gastrointestinal tolerance and any neuropsychiatric or behavioural changes during treatment.

Counselling the patient

Start as soon as possible after symptoms begin for the best effect.
Giving with food can reduce nausea, and a liquid is available for younger children.
Report any confusion, agitation or abnormal behaviour.

Evidence & guidelines

Use of oseltamivir for at-risk children during influenza circulation is supported by NICE technology appraisal guidance and UK public-health recommendations.

Reference: NICE TA168; PHE Influenza Guidelines; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways