Tamiflu (Oseltamivir) Dosing Guidelines
For adults and adolescents ≥13 years with influenza, the standard treatment dose is 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset. 1, 2
Treatment Dosing by Age and Weight
Adults and Adolescents (≥13 years)
- 75 mg orally twice daily for 5 days 1, 2
- Available as capsules or 12.5 mL of oral suspension (6 mg/mL concentration) 1, 2
- Must be started within 48 hours of symptom onset for maximum effectiveness 1
Pediatric Patients (1-12 years) - Weight-Based Dosing
- ≤15 kg (≤33 lb): 30 mg (5 mL) twice daily for 5 days 1, 2
- >15-23 kg (>33-51 lb): 45 mg (7.5 mL) twice daily for 5 days 1, 2
- >23-40 kg (>51-88 lb): 60 mg (10 mL) twice daily for 5 days 1, 2
- >40 kg (>88 lb): 75 mg (12.5 mL) twice daily for 5 days 1, 2
Infants (<12 months) - Age-Based Dosing
- 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1
- Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1
Preterm Infants - Postmenstrual Age-Based Dosing
Critical consideration: Preterm infants require substantially lower doses due to immature renal function 1
- <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1
- 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1
- >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1
Prophylaxis Dosing
Post-Exposure Prophylaxis (Start within 48 hours of exposure)
- Adults/adolescents ≥13 years: 75 mg once daily for 10 days 3, 2
- Children 1-12 years: Same weight-based doses as treatment, but once daily instead of twice daily for 10 days 1
- Infants 3-11 months: 3 mg/kg once daily for 10 days 1
- Infants <3 months: Prophylaxis not recommended unless situation is critical due to limited safety data 1
Seasonal Prophylaxis (Community Outbreak)
- Same dosing as post-exposure prophylaxis, but continued for up to 6 weeks 2
- Immunocompromised patients: May continue for up to 12 weeks 2
Renal Impairment Dose Adjustments
Mandatory dose reduction for creatinine clearance <60 mL/min 1
Moderate Renal Impairment (CrCl 10-30 mL/min)
- Treatment: 75 mg once daily (instead of twice daily) for 5 days 1, 2
- Prophylaxis: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 3
End-Stage Renal Disease
- Not recommended for patients not undergoing dialysis 2
Administration Guidance
Formulation Options
- Capsules: 30 mg, 45 mg, 75 mg 1, 2
- Oral suspension: 6 mg/mL concentration when reconstituted 1, 2
- Capsules can be opened and mixed with liquid if patient cannot swallow whole 1
Tolerability Enhancement
Take with food to significantly reduce nausea and vomiting 1, 4
- Nausea occurs in ~10% of adults and vomiting in ~9% when taken for treatment 1
- These gastrointestinal effects are mild, transient, and less severe when taken with food 1, 4
- Only ~1% of patients discontinue due to GI side effects 1
Critical Timing Considerations
The 48-hour window is crucial for treatment efficacy 1, 5
- Treatment initiated within 24 hours of symptom onset reduces illness duration by 37-40% compared to placebo 5
- Treatment initiated within 36 hours reduces illness duration by 25-30% 5
- Starting treatment >48 hours after symptom onset shows minimal benefit in most populations 6
Common Prescribing Pitfalls to Avoid
- Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily) - this is a common prescribing error 3
- Do not delay treatment waiting for laboratory confirmation - start based on clinical suspicion if within 48-hour window 1
- Do not forget renal dose adjustments - failure to reduce dose in renal impairment can lead to toxicity 1
- Avoid oseltamivir if live attenuated influenza vaccine (LAIV) given within past 2 weeks - may interfere with vaccine efficacy 1, 3
- Do not use standard adult dosing in elderly patients with renal impairment - age-related decline in renal function requires dose adjustment based on creatinine clearance, not age alone 1
Special Populations
Pregnancy
- No contraindication exists for oseltamivir use during pregnancy 1