Tamiflu (Oseltamivir) Treatment Regimen
For adults and adolescents ≥13 years with influenza, administer oseltamivir 75 mg orally twice daily for 5 days, initiated as soon as possible within 48 hours of symptom onset, though high-risk and hospitalized patients benefit even when treatment starts beyond 48 hours. 1, 2
Standard Dosing by Age and Weight
Adults and Adolescents (≥13 years)
- Treatment: 75 mg orally twice daily for 5 days 1, 2
- Prophylaxis: 75 mg orally once daily for 10 days (post-exposure) or up to 6 weeks (community outbreak) 1, 2
Pediatric Patients (1-12 years) - Weight-Based Dosing
- ≤15 kg: 30 mg twice daily (treatment) or once daily (prophylaxis) 1, 3, 2
- >15-23 kg: 45 mg twice daily (treatment) or once daily (prophylaxis) 1, 3, 2
- >23-40 kg: 60 mg twice daily (treatment) or once daily (prophylaxis) 1, 3, 2
- >40 kg: 75 mg twice daily (treatment) or once daily (prophylaxis) 1, 3, 2
Infants (2 weeks to <1 year)
Renal Dose Adjustments
Critical adjustments are required for patients with renal impairment to prevent drug accumulation: 1, 2
Treatment Dosing
- CrCl >60 mL/min: No adjustment needed (75 mg twice daily) 1, 2
- CrCl 30-60 mL/min: 30 mg twice daily 1, 2
- CrCl 10-30 mL/min: 30 mg once daily 1, 2
- ESRD on hemodialysis: 30 mg after each dialysis cycle 2
- ESRD not on dialysis: Not recommended 2
Prophylaxis Dosing
- CrCl 30-60 mL/min: 30 mg once daily 1, 2
- CrCl 10-30 mL/min: 30 mg every other day 1, 2
- ESRD on hemodialysis: 30 mg after alternate dialysis cycles 2
High-Risk Populations Requiring Immediate Treatment
The following patients should receive oseltamivir regardless of time since symptom onset, as they derive significant mortality benefit even when treatment is initiated beyond 48 hours: 1
- All hospitalized patients with suspected or confirmed influenza 1
- Children <2 years of age (especially infants <6 months) 1, 4
- Adults ≥65 years 1
- Pregnant and postpartum women (up to 2 weeks postpartum) 1
- Immunocompromised patients (including those on long-term corticosteroids, chemotherapy, HIV, transplant recipients) 1
- Patients with chronic medical conditions:
- Chronic cardiac disease (including congenital heart disease, hypertension with cardiac complications) 1
- Chronic pulmonary disease (asthma, COPD, cystic fibrosis, bronchiectasis) 1
- Chronic renal disease 1
- Chronic liver disease (including cirrhosis) 1
- Diabetes mellitus requiring medication 1
- Neurological diseases (cerebral palsy, epilepsy) 1
- Morbid obesity (BMI ≥40) 1
- Residents of long-term care facilities 1
Treatment Timing and Clinical Benefits
Optimal Window (Within 48 Hours)
- Reduces illness duration by 1-1.5 days (approximately 17.6-36 hours) 1, 5, 6
- Reduces symptom severity by 30-38% 1, 7
- Reduces pneumonia risk by 50% 1
- Reduces otitis media risk by 34% in children 1
- Earlier initiation within this window provides progressively greater benefit 7
Treatment Beyond 48 Hours
Do not withhold treatment in high-risk or hospitalized patients presenting after 48 hours, as substantial mortality benefit persists: 1
- Treatment up to 96 hours after symptom onset reduces mortality (OR 0.21 for death within 15 days) 1
- Hospitalized patients benefit from treatment initiated up to 5 days after symptom onset 1
- Immunocompromised patients may have prolonged viral shedding and benefit from late treatment 1
Critical Clinical Considerations
Do NOT Wait for Laboratory Confirmation
Initiate treatment empirically in high-risk patients during influenza season based on clinical presentation (acute onset of fever with cough or sore throat). 1
- Rapid antigen tests have poor sensitivity; negative results should not exclude treatment 1
- RT-PCR is the gold standard but takes longer; do not delay treatment while awaiting results 1
Administration Recommendations
- Take with food to reduce gastrointestinal side effects (nausea, vomiting) 1, 2, 5
- Complete the full 5-day course even if symptoms improve 1
- Use oral suspension (6 mg/mL) for patients unable to swallow capsules 2
Common Adverse Effects
- Nausea: 3.66% increased risk (NNTH = 28) 1
- Vomiting: 4.56% increased risk in adults (NNTH = 22); 5.34% in children (NNTH = 19) 1
- Gastrointestinal effects are transient, mild, and rarely lead to discontinuation 1, 5
- No established link between oseltamivir and neuropsychiatric events 1
Special Populations
Pregnant Women
- Treatment benefits outweigh risks; use standard adult dosing (75 mg twice daily) 1
- Lower exposure to active metabolite occurs in pregnancy, but predicted levels remain therapeutic 2
Immunocompromised Patients
- May require extended treatment duration beyond 5 days due to prolonged viral shedding 1
- Prophylaxis may be continued up to 12 weeks during community outbreaks 1, 2
Hepatic Impairment
- No dose adjustment needed for mild to moderate hepatic impairment 2
Post-Exposure Prophylaxis Indications
Initiate prophylaxis within 48 hours of exposure in: 1
- Household contacts of influenza-infected persons, especially high-risk individuals 1
- Healthcare workers in outbreak settings, particularly unvaccinated staff 1
- Residents of long-term care facilities during outbreaks (continue ≥2 weeks or until 1 week after outbreak ends) 1
- Unvaccinated high-risk patients during community outbreaks 1
Prophylactic efficacy ranges from 58.5-89% when started within 48 hours of exposure. 1
Important Caveats
- Oseltamivir is NOT a substitute for annual influenza vaccination 1, 2
- Resistance remains low (<5% in the United States for influenza A) 1
- If resistance is suspected, zanamivir is an alternative 1
- Oseltamivir appears somewhat less effective against influenza B compared to influenza A (8.5% vs 34% reduction in time to resolution) 1
- Patients with hereditary fructose intolerance should be informed that oral suspension contains sorbitol 1