💊 Oseltamivir (Tamiflu) is a neuraminidase inhibitor used to treat or prevent influenza A and B.
It is most effective if started within 48 hours of symptom onset or given promptly after close contact with a confirmed case.
Early treatment can shorten illness duration and reduce complications such as pneumonia, respiratory failure, and hospitalisation - particularly in older adults or those with comorbidities.
📘 About
- Always check the BNF entry here for the latest prescribing and renal-dose adjustment advice.
- Licensed for both treatment and post-exposure prophylaxis of influenza A and B.
- Resistance remains uncommon, but local surveillance data should be checked during outbreaks.
⚙️ Mode of Action
- Oseltamivir inhibits the viral neuraminidase enzyme on the surface of influenza virions.
- This prevents the release of new viral particles from infected epithelial cells, limiting spread within the respiratory tract.
- It is a prodrug, converted hepatically to the active metabolite oseltamivir carboxylate.
💊 Indications & Dose
- Treatment of influenza: 75 mg PO every 12 h for 5 days (start within 48 h of symptoms).
- Post-exposure prophylaxis: 75 mg PO once daily for 10 days following exposure.
- Renal impairment: Reduce dose if eGFR < 60 mL/min - check BNF for details.
⚠️ Cautions
- Use with care in renal impairment (dose adjustment required).
- Discuss risk–benefit in pregnancy and breastfeeding - may be used if benefits outweigh risks.
- Monitor for neuropsychiatric symptoms in adolescents (rare reports).
🚫 Contraindications
- Known hypersensitivity to oseltamivir or any excipient.
- Use cautiously if previous severe GI intolerance or allergic reaction.
💥 Adverse Effects
- Common: Nausea, vomiting, abdominal pain, headache, fatigue.
- Uncommon: Neuropsychiatric events (hallucinations, confusion - mainly children), arrhythmias, skin reactions, thrombocytopenia.
- Usually mild and self-limiting; take after food to improve tolerance.
🔄 Interactions
- No major interactions of clinical importance, but always review current medication list for renal-cleared antivirals.
- See BNF for comprehensive list.
📚 References
- BNF Online: Oseltamivir.
- Public Health England / UKHSA Influenza Guidelines.
- NICE NG163: COVID-19 rapid guideline - antibiotics and antivirals (includes influenza context).
🧠 Teaching Note
Oseltamivir has modest benefit in otherwise healthy adults but a clinically meaningful impact in frail or high-risk groups.
Clinicians should prioritise early testing and initiation in hospitalised or immunocompromised patients during influenza season.
🕓 Revisions
- 2025-10 - Content updated and expanded by Dr O’Kane (Makindo edition).
