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

Oseltamivir (Tamiflu) Dosing Recommendations

Standard Adult and Adolescent Dosing (≥13 years)

For treatment of influenza, administer oseltamivir 75 mg orally twice daily for 5 days in adults and adolescents ≥13 years of age. 1, 2, 3

• Initiate treatment within 48 hours of symptom onset for maximum benefit, which reduces illness duration by approximately 1-1.5 days 2, 4, 5
• For prophylaxis, use 75 mg once daily for 10 days following exposure, or up to 6 weeks during community outbreaks 2, 4, 3
• In immunocompromised patients, prophylaxis may be extended up to 12 weeks 3
• Administration with food significantly reduces gastrointestinal side effects (nausea/vomiting), which occur in 10-15% of patients 2, 4

Pediatric Dosing (1-12 years)

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

Treatment Dosing (twice daily for 5 days):

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

Prophylaxis Dosing (once daily for 10 days):

• Use the same weight-based doses as treatment, but administered once daily instead of twice daily 1, 3

Infant Dosing (<1 year)

For term infants, dosing is age-based and calculated per kilogram of body weight: 1, 2

Term Infants (≥2 weeks to <1 year):

• 0-8 months: 3 mg/kg per dose twice daily for treatment 1, 2, 3
• 9-11 months: 3.5 mg/kg per dose twice daily for treatment 1, 2
• Prophylaxis (3-8 months): 3 mg/kg once daily for 10 days 1
• Prophylaxis is NOT recommended for infants <3 months unless the situation is judged critical 1

Preterm Infants (Critical Distinction):

Never use standard term infant dosing (3 mg/kg) for preterm infants—this leads to toxic drug accumulation due to immature renal function. 1

Dose preterm infants based on postmenstrual age (PMA = gestational age + chronological age): 1

• <38 weeks PMA: 1.0 mg/kg per dose twice daily 1
• 38-40 weeks PMA: 1.5 mg/kg per dose twice daily 1
• >40 weeks PMA: 3.0 mg/kg per dose twice daily 1

Renal Impairment Dosing

Mandatory dose reductions are required for creatinine clearance <60 mL/min: 2, 4, 3

Adults with CrCl 10-30 mL/min:

• Treatment: 30 mg once daily for 5 days (instead of 75 mg twice daily) 1, 2, 3
• Prophylaxis: 30 mg once daily OR 75 mg every other day for 10 days (5 total doses) 1, 3

Pediatric Patients with CrCl 10-30 mL/min:

• Reduce the child's weight-based dose to once daily (instead of twice daily) for 5 days 1
• For prophylaxis, give half the standard once-daily dose given once daily, or the full once-daily dose every other day for 10 days 1

End-Stage Renal Disease:

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

Special Populations

Pregnant and Breastfeeding Women:

• Use standard adult dosing: 75 mg twice daily for 5 days 2, 4
• Breastfeeding is not a contraindication to oseltamivir use 2, 4

Elderly Patients (≥65 years):

• Use standard adult dosing (75 mg twice daily) if renal function is normal 2
• Mandatory dose reductions when creatinine clearance falls below 60 mL/min 2
• Do not reduce dose based on age alone—assess renal function as it declines with aging 2

Formulation and Administration

• Available as 30 mg, 45 mg, and 75 mg capsules and oral suspension (6 mg/mL when reconstituted) 1
• The oral suspension is the preferred formulation for patients who cannot swallow capsules 3
• Use an appropriate oral dosing dispensing device that accurately measures volume in mL 3
• For infants <1 year, provide a dosing device that can accurately measure and administer small volumes 3

Critical Pitfalls to Avoid

Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this leads to underdosing treatment or overdosing prophylaxis. 2, 4

• 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 1
• Never confuse GFR with creatinine clearance when calculating renal dosing adjustments 1
• Ensure infants are term (≥37 weeks gestation at birth)—if preterm, use postmenstrual age-based dosing 1
• Do not withhold treatment in high-risk or hospitalized patients presenting beyond 48 hours of symptom onset 4

Clinical Efficacy Evidence

• Standard-dose oseltamivir (75 mg twice daily for 5 days) was associated with an 82% reduction in odds of in-patient death in hospitalized patients with PCR-confirmed influenza B and A(H3N2) 6
• No benefit has been demonstrated for double-dose oseltamivir therapy or extending treatment beyond 5 days in most patient populations 7
• Oseltamivir may increase survival when used within 5 days of symptom onset in influenza H1N1-infected patients requiring ICU admission 7