What is the recommended Oseltamivir (antiviral medication) dose for treating influenza in adults and children of different ages and weights?

Oseltamivir Dosing Recommendations

For adults and adolescents ≥13 years, administer oseltamivir 75 mg orally twice daily for 5 days for treatment, or 75 mg once daily for prophylaxis, with dose reductions required for moderate-to-severe renal impairment (creatinine clearance 10-30 mL/min to 75 mg once daily for treatment or 30 mg once daily for prophylaxis). 1, 2, 3

Adult and Adolescent Dosing (≥13 years)

Treatment:

• Standard dose: 75 mg orally twice daily for 5 days 1, 2, 3
• Initiate within 48 hours of symptom onset for maximum benefit, though treatment beyond 48 hours still provides substantial benefit in hospitalized and high-risk patients 2
• May be taken with or without food, though administration with food improves gastrointestinal tolerability 1, 3

Prophylaxis:

• Post-exposure: 75 mg once daily for 10 days (initiate within 48 hours of exposure) 1, 2, 3
• Seasonal prophylaxis: 75 mg once daily for up to 6 weeks during community outbreaks 3
• Immunocompromised patients: May continue for up to 12 weeks 3

Pediatric Dosing (≥1 year to 12 years)

Weight-based dosing is essential for children ≥1 year: 1, 2, 3

Body Weight	Treatment Dose (twice daily × 5 days)	Prophylaxis Dose (once daily × 10 days)	Oral Suspension Volume (6 mg/mL)
≤15 kg (≤33 lb)	30 mg	30 mg	5 mL
>15-23 kg (>33-51 lb)	45 mg	45 mg	7.5 mL
>23-40 kg (>51-88 lb)	60 mg	60 mg	10 mL
>40 kg (>88 lb)	75 mg	75 mg	12.5 mL

4, 1, 2, 3

Infant Dosing (<1 year)

For term infants 0-8 months:

• Treatment: 3 mg/kg per dose twice daily for 5 days 1, 2, 3
• Prophylaxis: 3 mg/kg once daily for 10 days (for infants 3-11 months only) 1, 2

For infants 9-11 months:

• Treatment: 3.5 mg/kg per dose twice daily for 5 days 1, 2, 5

Critical caveat: Prophylaxis is not recommended for infants <3 months unless the situation is judged critical due to limited safety data 1, 2

Preterm Infant Dosing

Preterm infants require substantially lower doses based on postmenstrual age (PMA = gestational age + chronological age) due to immature renal function: 1, 2, 6

Postmenstrual Age	Treatment Dose (twice daily × 5 days)
<38 weeks PMA	1.0 mg/kg per dose
38-40 weeks PMA	1.5 mg/kg per dose
>40 weeks PMA	3.0 mg/kg per dose

1, 2, 6

Common pitfall: Never use standard term infant dosing for preterm infants—this can lead to drug accumulation and toxicity 6

Renal Impairment Adjustments

For creatinine clearance 10-30 mL/min (moderate-to-severe renal impairment): 4, 1, 2, 3

Treatment:

• 75 mg once daily (instead of twice daily) for 5 days 1, 2, 3

Prophylaxis:

• 30 mg once daily for 10 days, OR
• 75 mg every other day for 10 days (5 total doses) 1, 2, 3

Important consideration: The most critical factor in older adults is renal function, not age alone—dose reductions are mandatory when creatinine clearance falls below 30 mL/min 1

Contraindication: Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis 1, 3

Formulation and Administration

Available formulations: 1, 2, 3

• Capsules: 30 mg, 45 mg, 75 mg
• Oral suspension: 6 mg/mL when reconstituted (preferred for patients who cannot swallow capsules)

Administration pearls:

• Take with food to reduce nausea and vomiting (occurs in 5-15% of patients) 1, 3
• Capsules can be opened and contents mixed with liquid if needed 1
• If commercial suspension unavailable, pharmacies can compound suspension based on package insert instructions 1

Special Populations

Pregnancy:

• Same dosing as non-pregnant adults: 75 mg twice daily for treatment 2
• No dose adjustment needed throughout all trimesters or postpartum period 2
• Oseltamivir is preferred over zanamivir in pregnancy 2
• Breastfeeding is not a contraindication 2

Immunocompromised patients:

• Treat regardless of time since symptom onset 2
• May require extended treatment duration beyond 5 days if illness is prolonged 2
• Prophylaxis may be continued for up to 12 weeks 3

Drug Interactions

Live attenuated influenza vaccine (LAIV):

• Avoid LAIV within 48 hours before oseltamivir administration 1, 2
• Do not use oseltamivir for 14 days after LAIV vaccination 1, 2

Critical Timing Considerations

Treatment:

• Initiate within 48 hours of symptom onset for maximum benefit (reduces illness duration by 1-1.5 days) 2, 7
• Do not delay treatment while awaiting laboratory confirmation in high-risk patients 2
• Treatment after 48 hours still provides substantial benefit in hospitalized and high-risk patients 2

Prophylaxis:

• Initiate within 48 hours of exposure to infected individual 2, 3
• Protection lasts only as long as dosing is continued 3

Common Pitfalls to Avoid

• Do not confuse GFR with creatinine clearance when calculating renal dosing adjustments 6
• Do not use standard term infant dosing for preterm infants—they require significantly lower postmenstrual age-based dosing 1, 6
• Do not withhold treatment in high-risk patients presenting beyond 48 hours—they still derive substantial benefit 2
• Do not use weight-based dosing approved for older children in infants <1 year—they require mg/kg dosing 1, 2, 5