oseltamivir
neuraminidase inhibitor· Brands: TamifluPO
Mechanism of action
Oseltamivir is a prodrug that is metabolised to oseltamivir carboxylate, which selectively inhibits influenza A and B neuraminidase enzymes. This blocks the release of newly formed viral particles from infected cells, reducing viral replication and spread.
Pharmacokinetics
Oseltamivir is well absorbed orally and hydrolysed in the liver to the active metabolite, oseltamivir carboxylate. Bioavailability of the active form is around 75%. The metabolite is not further metabolised and is excreted renally via filtration and tubular secretion. The elimination half-life is about 6 to 10 hours, and dose reduction is needed in moderate to severe renal impairment.
Indications & dosing
Treatment of influenza A and B in adults
Start within 48 hours of symptom onset. Treat for 5 days.
- adult · PO: 75 mg twice daily · Start within 48 hours of symptom onset. Treat for 5 days.
Prophylaxis of influenza A and B in adults
Usually for 10 days after exposure, or up to 6 weeks during an outbreak.
- adult · PO: 75 mg once daily · Usually for 10 days after exposure, or up to 6 weeks during an outbreak.
Treatment of influenza A and B in children
Weight-based: 2 mg/kg twice daily, maximum 75 mg per dose. For children 1 year and above.
- pediatric · PO: 30–75 mg twice daily · Weight-based: 2 mg/kg twice daily, maximum 75 mg per dose. For children 1 year and above.
Prophylaxis of influenza A and B in children
Weight-based: 2 mg/kg once daily, maximum 75 mg per dose. For children 1 year and above.
- pediatric · PO: 30–75 mg once daily · Weight-based: 2 mg/kg once daily, maximum 75 mg per dose. For children 1 year and above.
Contraindications & precautions
- Known hypersensitivity to oseltamivir or any excipient · Rare but serious; do not use.
- Severe renal impairment (creatinine clearance less than 10 mL/min) without dialysis · Dose adjustment required; specialist advice advised.
- Adjust dose in renal impairment; monitor creatinine clearance.
- Monitor for unusual behaviour or neuropsychiatric symptoms, particularly in children and adolescents.
- Avoid concurrent use with live attenuated influenza vaccine; wait 48 hours after discontinuing oseltamivir.
- Use with caution in pregnancy and breastfeeding, weighing benefit against risk.
- Caution in patients with a history of psychiatric illness.
Adverse effects
- Nausea
- Vomiting
- Headache
- Diarrhoea
- Neuropsychiatric events (e.g. hallucinations, agitation)serious
- Anaphylaxisserious
- Stevens-Johnson syndromeserious
- Hepatitisserious
Renal & hepatic adjustment
- eGFR 60+: No adjustment needed. Usual dose: 75 mg twice daily for treatment, 75 mg once daily for prophylaxis.
- eGFR 30–59: Treatment: 75 mg once daily. Prophylaxis: 75 mg every other day.
- eGFR 10–29: Treatment: 75 mg every other day. Prophylaxis: 75 mg weekly.
- eGFR 0–9: Not recommended. If used, consider alternative. For haemodialysis: 30 mg after each dialysis session. (avoid)
Monitoring, pregnancy & toxicity
- Clinical response (fever, respiratory symptoms) · At start of treatment and during
- Neuropsychiatric symptoms (e.g., confusion, abnormal behaviour) · During treatment, especially in children and adolescents
- Renal function (creatinine clearance) in patients with renal impairment · Before and during treatment
- Pregnancy: Oseltamivir is recommended for the treatment and prophylaxis of influenza during pregnancy. The benefits of treatment generally outweigh the risks. Use standard dosing; monitor closely.
- Toxicity: Nausea, vomiting, abdominal pain · Supportive care; consider antiemetics; ensure hydration.
- Toxicity: Headache, dizziness, insomnia · Symptomatic treatment; monitor and discontinue if severe.
- Toxicity: Neuropsychiatric events (e.g., delirium, hallucinations, self-harm) especially in children and adolescents · Discontinue oseltamivir; seek immediate psychiatric evaluation.
- Toxicity: Overdose (e.g., severe vomiting) · General supportive measures; activated charcoal if recent ingestion; monitor for adverse effects.
Clinical notes
Oseltamivir is used for the treatment and prophylaxis of influenza A and B. Treatment should be started within 48 hours of symptom onset to be effective. Common adverse effects are nausea and vomiting, which may be reduced by taking with food. There have been rare reports of neuropsychiatric events, particularly in adolescents. It is not a substitute for influenza vaccination. Check local guidelines for dosing with renal impairment and during outbreaks.
Log in to read the full oseltamivir monograph
A free account unlocks the complete drug reference, the interaction checker, prescription practice and every other learning tool.
BNF; local formulary