Tamiflu (Oseltamivir) Dosing and Treatment Guidelines
Treatment Dosing
For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset for optimal efficacy. 1, 2
Adults and Adolescents (≥13 years)
- Standard dose: 75 mg orally twice daily for 5 days 1, 2
- Treatment should be initiated within 48 hours of symptom onset for maximum benefit, though treatment after 48 hours may still provide benefit in patients with moderate-to-severe or progressive disease 1
- Can be taken with or without food, though administration with meals may improve gastrointestinal tolerability 1, 2
Pediatric Patients (≥12 months)
Weight-based dosing for 5 days: 1, 2
- ≤15 kg (≤33 lb): 30 mg twice daily
- >15-23 kg (>33-51 lb): 45 mg twice daily
- >23-40 kg (>51-88 lb): 60 mg twice daily
- >40 kg (>88 lb): 75 mg twice daily
Infants (2 weeks to <12 months)
- 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 2
- Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 2
- FDA approved for use in infants as young as 2 weeks of age 1, 2
Preterm Infants
Dosing based on postmenstrual age (gestational age + chronological age): 1
- <38 weeks: 1.0 mg/kg twice daily for 5 days
- 38-40 weeks: 1.5 mg/kg twice daily for 5 days
- >40 weeks: 3.0 mg/kg twice daily for 5 days
The lower dosing for preterm infants is critical because immature renal function can lead to drug accumulation and toxicity if term infant doses are used 1
Prophylaxis Dosing
For post-exposure prophylaxis, initiate oseltamivir within 48 hours of contact with an infected individual. 2
Adults and Adolescents (≥13 years)
- Standard dose: 75 mg orally once daily 1, 2
- Duration: 10 days for post-exposure prophylaxis; up to 6 weeks for seasonal prophylaxis during community outbreak 1, 2
- Immunocompromised patients: May continue for up to 12 weeks 2
Pediatric Patients (≥1 year)
Use same weight-based doses as treatment, but once daily instead of twice daily: 1, 2
- ≤15 kg: 30 mg once daily
- >15-23 kg: 45 mg once daily
- >23-40 kg: 60 mg once daily
- >40 kg: 75 mg once daily
- Duration: 10 days post-exposure; up to 6 weeks during community outbreak 1, 2
Infants (3-11 months)
- 3-8 months: 3 mg/kg once daily for 10 days 1
- 9-11 months: 3.5 mg/kg once daily for 10 days 1
- <3 months: Not recommended unless situation judged critical due to limited safety and efficacy data 1
Renal Impairment Adjustments
For patients with creatinine clearance 10-30 mL/min, dose reduction is mandatory to prevent drug accumulation. 1, 2
Treatment Dosing in Renal Impairment
Prophylaxis Dosing in Renal Impairment
- CrCl 10-30 mL/min: Either 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 2
Formulations and Administration
Available Formulations
Suspension Dosing Volumes (6 mg/mL concentration)
Compounding Instructions
If commercially manufactured oral suspension is unavailable, capsules can be opened and contents mixed with simple syrup or Ora-Sweet SF (sugar-free) by retail pharmacies to achieve a final concentration of 6 mg/mL 1, 3
Clinical Efficacy and Timing
Early treatment provides optimal clinical benefit—initiate within 48 hours of symptom onset whenever possible. 1, 2
Treatment Benefits
- Reduces duration of illness by 0.7-1.5 days in general populations 4, 5, 6
- Greater efficacy (1.5-2.0 days reduction) when treatment initiated within 30 hours of symptom onset in febrile patients 6
- Reduces severity of illness by up to 38% compared with placebo 4
- Decreases incidence of secondary complications and antibiotic use 4
Treatment After 48 Hours
Treatment initiated after 48 hours of symptoms in patients with moderate-to-severe disease or progressive disease has been shown to provide some benefit and should be strongly considered 1
For ICU patients with H1N1 influenza, oseltamivir may improve survival when initiated within 5 days of symptom onset 7
High-Risk Populations
Treatment should be offered to children with presumed serious, complicated, or progressive disease, irrespective of influenza immunization status 1
Reviews by the CDC and WHO have consistently found that timely oseltamivir treatment can reduce risks of complications, including those resulting in hospitalization and death 1
Prophylaxis Efficacy
Oseltamivir prophylaxis achieves 67-74% protective efficacy against laboratory-confirmed influenza. 6
- Seasonal prophylaxis (75 mg once daily for 6 weeks) prevents development of naturally acquired influenza by >70% compared with placebo in unvaccinated healthy adults 4
- Post-exposure household prophylaxis (75 mg once daily for 7 days) significantly reduces risk of illness when administered within 48 hours of symptom onset in the index case 4
- Demonstrated 92% protective efficacy when used adjunctively in previously vaccinated high-risk elderly patients 4
Adverse Effects and Tolerability
The most common adverse effects are gastrointestinal—nausea and vomiting—which are mild, transient, and significantly reduced when oseltamivir is taken with food. 4, 6
Common Adverse Effects
- Nausea and vomiting: Most frequent (approximately 10% when taken with food, versus 5% with placebo) 4, 6
- Headache: Occurs in <5% of patients 6
- Upper respiratory tract symptoms: Usually <5% 6
Administration Strategy to Minimize GI Effects
Taking oseltamivir with food reduces gastrointestinal adverse effects from approximately 15% to 10% 1, 3, 2, 6
Special Populations
Pregnancy
Pregnant women should receive the same dosing as non-pregnant persons: 75 mg twice daily for 5 days for treatment 8
Pregnancy substantially increases risk of severe influenza complications, and the benefit-risk profile strongly favors treatment 8
Oseltamivir is preferred over zanamivir in pregnancy due to zanamivir's inhaled route and potential respiratory complications 8
Breastfeeding
Breastfeeding mothers requiring antivirals should receive oseltamivir, and it is not a reason to discontinue breastfeeding 1, 8
Chronic Cardiac or Respiratory Disease
Patients with chronic conditions can receive standard dosing 3
In patients with cardiac disease, oseltamivir significantly shortened median duration of acute febrile illness (44.0 hours vs 64.7 hours with placebo, p=0.026) 5
In patients with chronic obstructive airways disease, median duration of acute febrile illness was reduced (37.9 hours vs 53.8 hours with placebo, p=0.004) 5
Drug Interactions
Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir administration, and do not use oseltamivir for 14 days after LAIV vaccination. 8, 3
This interaction occurs because oseltamivir may inhibit replication of the live vaccine virus, potentially reducing vaccine efficacy 8
Common Pitfalls and Clinical Pearls
Pitfall: Delaying Treatment
Do not wait for laboratory confirmation before initiating empiric treatment in high-risk patients with suspected influenza—start within 48 hours of symptom onset 3
Pitfall: Incorrect Dosing in Preterm Infants
Never use term infant doses in preterm infants—this can lead to drug accumulation and toxicity due to immature renal function 1
Pitfall: Discontinuing Treatment Based on Negative Initial Tests
Patients with high suspicion of influenza should continue antiviral treatment regardless of negative initial test results, unless an alternative diagnosis is established 9
Clinical Pearl: Extended Duration in Severe Cases
While standard treatment duration is 5 days, treatment for at least 7 days or until clinical improvement is observed may be appropriate in critically ill patients 9
Clinical Pearl: Double-Dose Therapy
Double-dose oseltamivir therapy (150 mg twice daily) confers no significant survival benefit and is not recommended 7