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Neuraminidase Inhibitor (Antiviral)

Oseltamivir

Brand names: Tamiflu

Oseltamivir is an oral antiviral used to treat and prevent influenza, particularly in those at higher risk of complications.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

US labelling (FDA)

Reference — US labelling, may differ from UK

Treatment of influenza Adults and adolescents (13 years and older): 75 mg twice daily for 5 days ( 2.2 ) Pediatric patients 1 to 12 years of age: Based on weight twice daily for 5 days ( 2.2 ) Pediatric patients 2 weeks to less than 1 year of age: 3mg/kg twice daily for 5 days ( 2.2 ) Renally impaired adult patients (creatinine clearance >30 to 60 mL/min): Reduce to 30 mg twice daily for 5 days ( 2.4 ) Renally impaired adult patients (creatinine clearance >10 to 30 mL/min): Reduce to 30 mg once daily for 5 days ( 2.4 ) ESRD patients on hemodialysis: Reduce to 30 mg immediately and then 30 mg after every hemodialysis cycle. Treatment duration not to exceed 5 days ( 2.4 ) ESRD patients on …

Source: US FDA prescribing information (openFDA / DailyMed), label dated 2024-05-15. Accessed 2026-06-12. US dosing and indications can differ from UK practice — use UK sources for prescribing decisions.

Clinical monograph

How it works

It inhibits the viral neuraminidase enzyme, preventing release of new virus particles from infected cells.

Prescribing in practice

  • It is most effective when started early — ideally within 48 hours of symptom onset (or of exposure for prophylaxis).
  • Nausea and vomiting are the commonest effects (taking it with food helps).
  • Reduce the dose in renal impairment.

Monitoring

No routine monitoring; review the clinical response.

Counselling the patient

  • Start it as soon as possible after symptoms begin.
  • Take it with food to reduce nausea.
  • It shortens illness but is not a substitute for vaccination.

Evidence & guidelines

Recommended for treatment and post-exposure prophylaxis of influenza in at-risk groups during circulating influenza (NICE TA158; UKHSA guidance).

Reference: NICE NG172; PHE Influenza Seasonal Report; MHRA Drug Safety; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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