What is the recommended dose and prescription directions for Tamiflu (Oseltamivir) in patients with influenza, including pediatric and adult populations with varying weights and potential Impaired renal function?

Tamiflu (Oseltamivir) Dosing and Prescription Directions

For adults and adolescents ≥13 years, prescribe Tamiflu 75 mg orally twice daily for 5 days for treatment, or 75 mg once daily for 10 days for prophylaxis, with mandatory dose reductions for renal impairment (creatinine clearance <60 mL/min). 1, 2

Adult and Adolescent Dosing (≥13 years)

Treatment regimen:

• 75 mg orally twice daily for 5 days 1, 2
• Initiate within 48 hours of symptom onset for maximum benefit (reduces illness duration by 1-1.5 days) 3, 4
• Can be taken with or without food, though administration with meals significantly reduces nausea and vomiting (occurs in 10-15% of patients) 1, 3

Prophylaxis regimen:

• 75 mg orally once daily for 10 days after exposure 1, 2
• For community outbreak: 75 mg once daily for up to 6 weeks 2

Pediatric Dosing (Children ≥1 year)

Weight-based dosing is mandatory for children—use the following treatment doses twice daily for 5 days: 1

Body Weight	Treatment Dose (twice daily)	Prophylaxis Dose (once daily)
≤15 kg (≤33 lb)	30 mg	30 mg
>15-23 kg (>33-51 lb)	45 mg	45 mg
>23-40 kg (>51-88 lb)	60 mg	60 mg
>40 kg (>88 lb)	75 mg	75 mg

1

Infant Dosing (<1 year)

Term infants require age-specific dosing: 1, 5

• Infants 9-11 months: 3.5 mg/kg per dose twice daily for treatment 1
• Infants 0-8 months: 3 mg/kg per dose twice daily for treatment 1, 5
• Prophylaxis for infants 3-8 months: 3 mg/kg once daily for 10 days 1
• Prophylaxis NOT recommended for infants <3 months unless situation is critical due to limited safety data 1

Critical pitfall: Never use term infant dosing (3 mg/kg) for preterm infants—they require substantially lower doses based on postmenstrual age due to immature renal function: 5

• <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 1, 5

Renal Impairment Dosing Adjustments

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

For CrCl 10-30 mL/min:

• Treatment: 30 mg once daily (not twice daily) for 5 days 1, 2
• Prophylaxis: 30 mg once daily OR 75 mg every other day for 10 days (5 total doses) 1, 2

For ESRD on hemodialysis:

• Treatment: 30 mg immediately, then 30 mg after every hemodialysis cycle (not to exceed 5 days) 2
• Prophylaxis: 30 mg immediately, then 30 mg after alternate hemodialysis cycles 2

For ESRD on CAPD:

• Treatment: Single 30 mg dose immediately 2
• Prophylaxis: 30 mg immediately, then 30 mg once weekly 2

Formulation and Administration

Available formulations: 1

• Capsules: 30 mg, 45 mg, 75 mg
• Oral suspension: 6 mg/mL when reconstituted

Suspension dosing volumes (6 mg/mL concentration): 1

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

Prescription Directions

For adults (treatment): "Take 75 mg by mouth twice daily with food for 5 days. Start as soon as possible after flu symptoms begin."

For adults (prophylaxis): "Take 75 mg by mouth once daily with food for 10 days after exposure to influenza."

For children (example: 20 kg child, treatment): "Give 45 mg (7.5 mL of suspension) by mouth twice daily with food for 5 days."

Critical Pitfalls to Avoid

Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this leads to underdosing treatment or overdosing prophylaxis. 3, 6

Always take with food to reduce gastrointestinal side effects (nausea/vomiting occurs in approximately 10-15% of patients). 1, 3

Never use weight-based pediatric unit doses (30 mg, 45 mg, 60 mg, 75 mg) in infants <1 year—these doses are too high. Infants require mg/kg dosing. 5

Assess renal function in elderly patients—dose reduction is mandatory when creatinine clearance falls below 60 mL/min, not based on age alone. 6