What is the recommended dose of Tamiflu (oseltamivir) for a patient with influenza, considering age, weight, and renal function?

Tamiflu (Oseltamivir) Dosing Recommendations

For adults and adolescents ≥13 years, the standard treatment dose is 75 mg orally twice daily for 5 days, and prophylaxis is 75 mg once daily for 10 days, with mandatory dose reductions required for renal impairment. 1, 2, 3

Adult and Adolescent Dosing (≥13 years)

• Treatment: 75 mg orally twice daily for 5 days 1, 2, 3
• Prophylaxis: 75 mg once daily for 10 days (post-exposure) or up to 6 weeks (seasonal prophylaxis during community outbreak) 1, 2, 3
• Treatment should 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 4
• Can be taken with or without food, though administration with meals significantly improves gastrointestinal tolerability 1, 2

Pediatric Dosing (1-12 years)

Weight-based dosing is mandatory for children, with specific doses based on body weight: 1, 2, 3

Treatment (twice daily for 5 days):

• ≤15 kg: 30 mg twice daily 1, 2, 3
• >15-23 kg: 45 mg twice daily 1, 2, 3
• >23-40 kg: 60 mg twice daily 1, 2, 3
• >40 kg: 75 mg twice daily 1, 2, 3

Prophylaxis (once daily for 10 days):

• Same weight-based doses as treatment, but administered once daily instead of twice daily 1, 2, 3

Infant Dosing (<1 year)

Term infants require age-specific dosing based on months of age: 1, 2

Treatment:

• 0-8 months: 3 mg/kg per dose twice daily for 5 days 1, 2
• 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 2

Prophylaxis:

• 3-11 months: 3 mg/kg once daily for 10 days 1, 5
• Not recommended for infants <3 months unless situation is critical due to limited safety data 1

Preterm Infant Dosing

Preterm infants require significantly lower doses based on postmenstrual age (gestational age + chronological age) due to immature renal function: 1

• <38 weeks postmenstrual age: 1.0 mg/kg per dose twice daily 1
• 38-40 weeks postmenstrual age: 1.5 mg/kg per dose twice daily 1
• >40 weeks postmenstrual age: 3.0 mg/kg per dose twice daily 1
• For extremely preterm infants (<28 weeks), consult a pediatric infectious disease physician 1

Critical Pitfall:

Never use term infant dosing (3 mg/kg) for preterm infants—this leads to toxic drug concentrations due to immature renal function. 2, 5

Renal Impairment Dosing

Dose adjustments are mandatory for creatinine clearance <60 mL/min: 1, 2

For CrCl 10-30 mL/min:

• Treatment: 75 mg once daily (instead of twice daily) for 5 days 1, 2
• Prophylaxis: 30 mg once daily for 10 days OR 75 mg every other day for 10 days (5 total doses) 1, 2

For end-stage renal disease:

• Oseltamivir is not recommended for patients with end-stage renal disease not undergoing dialysis 3

Formulation and Administration

Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted): 1, 3

Oral suspension dosing volumes:

• 30 mg dose = 5 mL 1, 3
• 45 mg dose = 7.5 mL 1, 3
• 60 mg dose = 10 mL 1, 3
• 75 mg dose = 12.5 mL 1, 3

Special Populations

Pregnancy:

• Pregnant women receive the same dosing as non-pregnant adults: 75 mg twice daily for 5 days 2, 4
• Breastfeeding is not a contraindication to oseltamivir use 2, 4

Elderly (≥65 years):

• Standard adult dosing (75 mg twice daily) with normal renal function 2
• Mandatory dose reduction when creatinine clearance falls below 60 mL/min 2

Immunocompromised:

• May require extended prophylaxis up to 12 weeks during community outbreaks 3
• May require extended treatment duration beyond 5 days if illness is prolonged 4

Critical Timing Considerations

• Treatment initiation within 48 hours of symptom onset reduces illness duration by 1-1.5 days 2, 4
• Prophylaxis should be started within 48 hours of exposure to infected individuals 2, 4
• Treatment should not be delayed while waiting for laboratory confirmation in high-risk patients, as rapid antigen tests have poor sensitivity 4

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
• Do not use GFR interchangeably with creatinine clearance for dose adjustments 5
• Taking oseltamivir with food significantly reduces gastrointestinal side effects (nausea/vomiting), which occur in approximately 10-15% of patients 2, 5
• Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir and do not use oseltamivir for 14 days after LAIV vaccination 4