What is the recommended dosing of Tamiflu (oseltamivir) for adults and children with influenza, considering factors such as weight, renal impairment, and pregnancy?

Tamiflu (Oseltamivir) Dosing Recommendations

Adult and Adolescent Dosing (≥13 years)

For adults and adolescents 13 years and older, the standard treatment dose is 75 mg orally twice daily for 5 days, and prophylaxis is 75 mg once daily for 10 days (or up to 6 weeks during community outbreaks). 1

• Treatment should be initiated within 48 hours of symptom onset for maximum benefit, reducing illness duration by approximately 1-1.5 days 2, 3
• Administration with food significantly improves gastrointestinal tolerability, reducing nausea and vomiting which occur in approximately 10-15% of patients 4, 2
• The oral suspension formulation provides 6 mg/mL concentration; the 75 mg dose equals 12.5 mL of suspension 4, 1

Pediatric Dosing (1-12 years)

Weight-based dosing is mandatory for children, with specific doses determined by body weight rather than age. 1

Treatment Dosing (twice daily for 5 days):

• ≤15 kg: 30 mg twice daily (5 mL of suspension) 4, 1
• >15-23 kg: 45 mg twice daily (7.5 mL of suspension) 4, 1
• >23-40 kg: 60 mg twice daily (10 mL of suspension) 4, 1
• >40 kg: 75 mg twice daily (12.5 mL of suspension) 4, 1

Prophylaxis Dosing (once daily for 10 days):

• Same weight-based doses as treatment, but administered once daily instead of twice daily 1
• Duration may extend up to 6 weeks during community outbreaks 1

Infant Dosing (<1 year)

For term infants aged 2 weeks to <1 year, the dose is 3 mg/kg per dose twice daily for 5 days. 4, 1

• This calculates to 0.5 mL/kg of the 6 mg/mL suspension per dose 1
• For an 8 kg infant, this equals 24 mg (4 mL) per dose 5
• Critical warning: This 3 mg/kg dosing applies ONLY to term infants—never use this dose for preterm infants 4, 5
• Prophylaxis is NOT recommended for infants <3 months unless the situation is judged critical, due to limited safety data 4

Preterm Infant Dosing

Preterm infants require substantially lower doses based on postmenstrual age (gestational age + chronological age) due to immature renal function. 4

• <38 weeks postmenstrual age: 1.0 mg/kg per dose twice daily for 5 days 4
• 38-40 weeks postmenstrual age: 1.5 mg/kg per dose twice daily for 5 days 4
• >40 weeks postmenstrual age: 3.0 mg/kg per dose twice daily for 5 days 4
• For extremely preterm infants (<28 weeks), consult a pediatric infectious disease physician 4

Common pitfall: Using term infant dosing (3 mg/kg) for preterm infants leads to toxic drug concentrations and must be avoided 4, 5

Renal Impairment Dosing

Dose adjustments are mandatory for patients with creatinine clearance <60 mL/min. 4, 2

Treatment Dosing:

• CrCl 30-60 mL/min: 30 mg twice daily for 5 days 1
• CrCl 10-30 mL/min: 30 mg once daily for 5 days 4, 1
• ESRD on hemodialysis: 30 mg immediately, then 30 mg after every hemodialysis cycle (not to exceed 5 days) 1
• ESRD on CAPD: Single 30 mg dose immediately 1

Prophylaxis Dosing:

• CrCl 30-60 mL/min: 30 mg once daily 1
• CrCl 10-30 mL/min: 30 mg once every other day for 10 days (5 total doses) OR 30 mg once daily 4, 1
• ESRD on hemodialysis: 30 mg immediately, then 30 mg after alternate hemodialysis cycles 1
• ESRD on CAPD: 30 mg immediately, then 30 mg once weekly 1

Important caveat: Oseltamivir is NOT recommended for patients with end-stage renal disease not undergoing dialysis 1

Emerging evidence concern: Current dosing recommendations for mild to moderate renal impairment may delay achievement of therapeutic concentrations in the critical first 24 hours, potentially reducing efficacy 6. The first dose should be 75 mg regardless of renal function, with subsequent doses adjusted based on creatinine clearance 6.

Pregnancy and Breastfeeding

Pregnant women receive the same dosing as non-pregnant adults: 75 mg twice daily for 5 days for treatment, or 75 mg once daily for prophylaxis. 2, 7

• Breastfeeding is not a contraindication to oseltamivir use 2, 7

Critical Timing Considerations

Treatment must be initiated within 48 hours of symptom onset for maximum benefit, though should not be withheld in high-risk or hospitalized patients presenting beyond 48 hours. 2, 7, 1

• Earlier initiation (within 24 hours) provides greater benefit, reducing illness duration by up to 40% compared to placebo 3
• Post-exposure prophylaxis should be started within 48 hours of exposure to infected individuals 2, 7
• Seasonal prophylaxis should be initiated during community outbreaks 1

Formulation and Administration

Oseltamivir is available as 30 mg, 45 mg, and 75 mg capsules, and as powder for oral suspension that reconstitutes to 6 mg/mL concentration. 4, 5

• If commercially manufactured suspension is unavailable, capsules can be opened and contents mixed with simple syrup or Ora-Sweet SF by pharmacies to achieve 6 mg/mL concentration 4
• Use an appropriate oral dosing device that accurately measures volume in mL 1
• For infants <1 year, provide a dosing device capable of measuring small volumes accurately 1

Common Pitfalls to Avoid

Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this leads to underdosing treatment or overdosing prophylaxis. 2, 7

Never use weight-based dosing intended for children ≥1 year (30 mg, 45 mg, 60 mg, 75 mg unit doses) in infants <1 year—these doses are too high. 5

Do not use term infant dosing for preterm infants—this causes toxic drug accumulation due to immature renal function. 4, 5

Ensure renal function assessment before dosing, as failure to adjust for renal impairment can lead to drug accumulation and toxicity. 4, 2