Oseltamivir (Tamiflu) Dosing and Administration
Treatment Dosing
For treatment of influenza, oseltamivir should be initiated within 48 hours of symptom onset at 75 mg orally twice daily for 5 days in adults and adolescents ≥13 years, with weight-based dosing for children. 1, 2
Adults and Adolescents (≥13 years)
- 75 mg orally twice daily for 5 days 1, 3, 2
- Can be taken with or without food, though administration with meals improves gastrointestinal tolerability 1, 3, 2
Pediatric Patients (≥12 months to 12 years)
Weight-based dosing for 5 days: 1, 3, 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, 3, 2
- Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 3, 2
Preterm Infants
Dosing based on postmenstrual age (gestational age + chronological age): 3, 4
- <38 weeks postmenstrual age: 1.0 mg/kg twice daily
- 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily
- >40 weeks postmenstrual age: 3.0 mg/kg twice daily
Prophylaxis Dosing
For prophylaxis, use the same weight-based doses as treatment but administered once daily instead of twice daily for at least 10 days following exposure. 1, 3, 2
Adults and Adolescents (≥13 years)
- 75 mg orally once daily 1, 3, 2
- Duration: 10 days after household exposure, up to 6 weeks during community outbreak 1, 2
- In immunocompromised patients, may continue up to 12 weeks 2
Pediatric Patients (≥1 year to 12 years)
Same weight-based doses as treatment, but once daily for 10 days: 1, 3, 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
Infants (3-11 months)
- 3-11 months: 3 mg/kg once daily for 10 days 3, 2
- Prophylaxis NOT recommended for infants <3 months unless situation judged critical due to limited safety data 1, 3
Renal Impairment Adjustments
Dose adjustment is mandatory for patients with creatinine clearance 10-30 mL/min: 1, 3, 2
- Treatment: 75 mg once daily for 5 days (instead of twice daily)
- Prophylaxis: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses)
Formulations and Administration
Available Formulations 1, 3, 2
- Capsules: 30 mg, 45 mg, 75 mg
- Oral suspension: 6 mg/mL when reconstituted from powder
Oral Suspension Dosing Volumes 1, 2
- 30 mg dose = 5 mL
- 45 mg dose = 7.5 mL
- 60 mg dose = 10 mL
- 75 mg dose = 12.5 mL
Compounding Alternative
If commercial suspension unavailable, capsules may be opened and contents mixed with simple syrup or Ora-Sweet SF (sugar-free) by retail pharmacies to achieve 6 mg/mL concentration 1
Critical Timing Considerations
Treatment must be initiated within 48 hours of symptom onset for maximum effectiveness. 1, 4, 2 Earlier initiation provides progressively better outcomes—treatment started within 12 hours of fever onset reduces illness duration by 3.1 days (41%) more than treatment started at 48 hours 5. However, treatment after 48 hours in patients with moderate-to-severe or progressive disease has shown some benefit and should be strongly considered 1.
Common Adverse Effects and Management
The most common adverse effects are nausea and vomiting, occurring in approximately 1 in 7 patients (versus 1 in 12 on placebo) 3, 6. These are typically:
- Mild and transient 1, 7
- Occur primarily with first dosing 5
- Significantly reduced when taken with food 3, 7, 8
- Rarely result in discontinuation (overall discontinuation rate 1.8%) 5
Other adverse effects include headache, diarrhea, and upper respiratory symptoms 3, 8
Important Drug Interactions
Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination 3, as the antiviral may interfere with vaccine efficacy.
Clinical Efficacy Evidence
Reviews by the CDC, WHO, and independent investigators consistently demonstrate that timely oseltamivir treatment reduces risks of complications, hospitalizations, and death 1. In proven influenza cases, oseltamivir reduces:
- Illness duration by 0.7-1.5 days in general populations 7, 8
- Illness duration by up to 3.1 days when started within 12 hours 5
- Severity of illness by up to 38% 7
- Duration of fever by 19-29% 6
- Secondary complications and antibiotic use 7
Efficacy is similar for both influenza A and B infections 6. Treatment is particularly important for children <2 years (increased hospitalization risk), patients with chronic cardiac/respiratory disease, and those with severe or progressive illness 1.