What is the recommended dosing for Tamiflu (oseltamivir) in the treatment of influenza?

Tamiflu (Oseltamivir) Dosing Recommendations

For adults and adolescents ≥13 years, the standard treatment dose is 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset. 1, 2

Adult and Adolescent Dosing (≥13 years)

• Treatment: 75 mg orally twice daily for 5 days (equivalent to 12.5 mL of oral suspension twice daily) 1, 2
• Prophylaxis: 75 mg orally once daily for at least 10 days following close contact with an infected individual, or up to 6 weeks during a community outbreak 1, 2
• In immunocompromised patients, prophylaxis may be continued for up to 12 weeks 2

Pediatric Dosing (≥12 months)

Weight-based dosing is essential for children 12 months and older: 1, 2

• ≤15 kg (≤33 lb): 30 mg (5 mL) twice daily for treatment; once daily for prophylaxis 1, 2
• >15-23 kg (>33-51 lb): 45 mg (7.5 mL) twice daily for treatment; once daily for prophylaxis 1, 2
• >23-40 kg (>51-88 lb): 60 mg (10 mL) twice daily for treatment; once daily for prophylaxis 1, 2
• >40 kg (>88 lb): 75 mg (12.5 mL) twice daily for treatment; once daily for prophylaxis 1, 2

Infant Dosing (<12 months)

Age-based dosing applies for infants: 1, 3

• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 3
• Term infants 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 3
• Prophylaxis is not recommended for infants <3 months unless the situation is judged critical due to limited safety data 1

Preterm Infant Dosing

Dosing for preterm infants is based on postmenstrual age (gestational age + chronological age): 1, 3

• <38 weeks postmenstrual age: 1.0 mg/kg per dose twice daily 1, 3
• 38-40 weeks postmenstrual age: 1.5 mg/kg per dose twice daily 1, 3
• >40 weeks postmenstrual age: 3.0 mg/kg per dose twice daily 1, 3

Renal Impairment Adjustments

Dose reduction is mandatory for patients with moderate to severe renal impairment: 1, 3

• CrCl 10-30 mL/min (treatment): 75 mg once daily for 5 days 1, 3
• CrCl 10-30 mL/min (prophylaxis): 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 3

Critical Timing Considerations

Treatment must be initiated within 48 hours of symptom onset for maximum effectiveness. 1, 3 Earlier initiation provides greater benefit—treatment within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours, while treatment within 24 hours provides an additional 53.9 hours of benefit 4. The drug blocks viral neuraminidase, which is only effective during active viral replication 4.

Formulation and Administration

Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted). 1, 2

• Administration with food is recommended to improve gastrointestinal tolerability, as nausea and vomiting occur in approximately 10% of patients 1, 4
• Capsules can be opened and mixed with liquid for patients unable to swallow whole capsules 1
• If commercial suspension is unavailable, pharmacies can compound a suspension at 6 mg/mL concentration 1

Common Pitfalls to Avoid

• Do not delay treatment waiting for laboratory confirmation—initiate based on clinical suspicion during influenza season 3
• Do not use standard adult dosing in children—weight-based dosing is critical to achieve therapeutic levels, as children eliminate the drug faster than adults 5
• Do not forget renal dose adjustments—failure to reduce dose in renal impairment can lead to toxicity 1
• Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination 1

Special Populations

Higher doses (150 mg twice daily) have been studied in hospitalized adults but showed no additional benefit for influenza A infections compared to standard dosing, though some benefit was observed for influenza B 6. Standard dosing remains recommended for routine use 1, 2.