Oseltamivir (Tamiflu) Dosing and Clinical Use Guidelines
Treatment Dosing
Oseltamivir 75 mg orally twice daily for 5 days is the standard treatment regimen for adults and adolescents ≥13 years with influenza A or B. 1, 2, 3
Pediatric Weight-Based Dosing (≥12 months)
- ≤15 kg (≤33 lb): 30 mg twice daily for 5 days 1, 2, 3
- >15–23 kg (>33–51 lb): 45 mg twice daily for 5 days 1, 2, 3
- >23–40 kg (>51–88 lb): 60 mg twice daily for 5 days 1, 2, 3
- >40 kg (>88 lb): 75 mg twice daily for 5 days 1, 2, 3
Infant Dosing (<12 months)
- Term infants 0–8 months: 3.0 mg/kg per dose twice daily for 5 days 1, 3
- Infants 9–11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 3
Preterm Infant Dosing (Post-Menstrual Age-Based)
- <38 weeks PMA: 1.0 mg/kg twice daily for 5 days 1
- 38–40 weeks PMA: 1.5 mg/kg twice daily for 5 days 1
- >40 weeks PMA: 3.0 mg/kg twice daily for 5 days 1
Critical pitfall: Using term-infant dosing for preterm infants causes toxic drug accumulation due to immature renal function; always calculate dose based on post-menstrual age (gestational age + chronologic age). 1
Post-Exposure Prophylaxis Dosing
Adults and adolescents ≥13 years: 75 mg once daily for 10 days after household exposure 1, 2, 3
Pediatric Prophylaxis (≥12 months)
- Use the same weight-based doses as treatment but once daily instead of twice daily for 10 days 1, 3
- Infants 3–11 months: 3.0 mg/kg once daily for 10 days 1
- Infants <3 months: Prophylaxis is not recommended unless the situation is judged critical due to limited safety data 1, 3
Renal Dose Adjustments
Dose reductions are mandatory for creatinine clearance ≤60 mL/min to prevent drug accumulation and toxicity. 1, 2, 3
| Creatinine Clearance | Treatment Dose | Prophylaxis Dose |
|---|---|---|
| >30–60 mL/min | 30 mg twice daily × 5 days | 30 mg once daily |
| 10–30 mL/min | 30 mg once daily × 5 days or 75 mg once daily × 5 days | 30 mg once daily or 75 mg every other day |
| ESRD on hemodialysis | 30 mg immediately, then 30 mg after each dialysis session (max 5 days) | 30 mg immediately, then 30 mg after alternate dialysis sessions |
| ESRD on CAPD | Single 30 mg dose | 30 mg immediately, then 30 mg once weekly |
| ESRD not on dialysis | Not recommended | Not recommended |
Timing of Initiation
Treatment should be initiated within 48 hours of symptom onset for maximum benefit, reducing illness duration by approximately 1–1.5 days (16.8–29 hours). 1, 2, 4, 5
High-Risk Patients Who Benefit Beyond 48 Hours
Do not withhold oseltamivir in the following populations even if presenting >48 hours after symptom onset, as mortality benefit persists up to 96 hours: 1, 6
- Hospitalized patients with severe or progressive illness 1, 6
- Children <2 years of age 1, 6
- Adults ≥65 years 1, 6
- Pregnant or postpartum women (within 2 weeks) 1, 6
- Immunocompromised patients (HIV, chemotherapy, long-term corticosteroids ≥20 mg prednisone daily for >2 weeks, transplant recipients) 1, 6
- Chronic cardiac disease (congenital heart disease, ischemic heart disease, hypertension with cardiac complications) 1, 6
- Chronic respiratory disease (asthma, COPD, cystic fibrosis, bronchiectasis) 1, 6
- Diabetes mellitus requiring insulin or oral agents 1, 6
- Chronic renal disease (nephrotic syndrome, transplant, dialysis) 1, 6
- Chronic liver disease (cirrhosis) 1, 6
- Neurological disorders (cerebral palsy, epilepsy, neuromuscular disease) 1, 6
- Residents of long-term care facilities 1, 6
In hospitalized patients with influenza pneumonia or suspected secondary bacterial complications, oseltamivir initiated up to 96 hours after symptom onset reduces mortality (OR 0.21 for death within 15 days). 1, 6
Formulations and Administration
- Capsules: 30 mg, 45 mg, 75 mg 1, 3
- Oral suspension: 6 mg/mL after reconstitution 1, 3
- 30 mg dose = 5 mL
- 45 mg dose = 7.5 mL
- 60 mg dose = 10 mL
- 75 mg dose = 12.5 mL
Administration with food significantly reduces nausea and vomiting (the most common adverse effects, occurring in ~10–15% of patients) without affecting antiviral efficacy. 1, 4, 5
If commercial suspension is unavailable, capsules may be opened and mixed with sweetened liquid (simple syrup or Ora-Sweet SF) to achieve 6 mg/mL concentration. 1
For infants, use a calibrated 3–5 mL oral syringe for accurate measurement; household spoons or the syringe supplied with commercial product are inadequate for small volumes. 1
Contraindications
Known serious hypersensitivity to oseltamivir or any component of the formulation. 3
Oseltamivir is NOT contraindicated in: 1
- Pregnancy (benefits outweigh risks; use standard adult dosing) 1
- Breastfeeding 1
- Asthma, COPD, or other chronic respiratory disease 1
- Chronic cardiac disease, diabetes, immunodeficiency 1
- Mild febrile illness or fever alone 1
Common Adverse Effects
Treatment Studies
- Nausea: 3.66% increased risk (NNTH = 28) 7, 8
- Vomiting in adults: 4.56% increased risk (NNTH = 22) 7, 8
- Vomiting in children: 5.34% increased risk (NNTH = 19) 7, 8
- Headache 3, 7
Prophylaxis Studies
- Headache: 3.15% increased risk on-treatment (NNTH = 32) 7, 8
- Nausea: 4.15% increased risk on-treatment (NNTH = 25) 7, 8
- Psychiatric events: 1.06% increased risk during combined on- and off-treatment periods (NNTH = 94) 7, 8
- Renal events: 0.67% increased risk on-treatment 7, 8
Gastrointestinal effects are mild, transient, resolve within 1–2 days, and rarely lead to discontinuation (~1% of patients). 1, 4, 5
No established causal link exists between oseltamivir and neuropsychiatric events despite early reports; influenza infection itself causes delirium, hallucinations, and abnormal behavior. 1
Clinical Benefits
Treatment Benefits
- Reduces illness duration by 16.8–29 hours (1–1.5 days) when started within 48 hours 1, 2, 4, 5
- Reduces pneumonia risk by 50% (investigator-mediated, unverified pneumonia; NNTB = 100) 1, 6, 7
- Reduces otitis media in children by 34% 1, 6, 8
- Reduces secondary complications requiring antibiotics by 35% 6, 4
- Reduces mortality in hospitalized patients (OR 0.21 for death within 15 days) 1, 6
Prophylaxis Benefits
- Reduces symptomatic influenza in individuals by 74–82% (NNTB = 33) 1, 4, 8
- Reduces symptomatic influenza in households by 58.5–89% (NNTB = 7) when started within 48 hours of exposure 1, 4, 8
Important Clinical Caveats
Do not wait for laboratory confirmation before initiating treatment in high-risk patients during influenza season; rapid antigen tests have poor sensitivity, and negative results should not exclude treatment. 1, 6
Complete the full 5-day course even if symptoms improve before day 5 to ensure adequate viral suppression and prevent resistance. 1, 2
Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination. 1, 3
Oseltamivir is not a substitute for annual influenza vaccination, which remains the primary prevention strategy. 1, 6
For patients with hereditary fructose intolerance, note that oseltamivir oral suspension contains sorbitol, which may cause dyspepsia and diarrhea. 1