What is the recommended dosing for Tamiflu (oseltamivir) in patients with influenza?

Tamiflu (Oseltamivir) Dosing Guidelines

Standard Adult and Adolescent Dosing

For adults and adolescents ≥13 years, the recommended dose is 75 mg orally twice daily for 5 days for treatment, and 75 mg once daily for prophylaxis. 1, 2

• Treatment must be initiated within 48 hours of symptom onset for maximum effectiveness 1, 3
• The oral suspension equivalent is 12.5 mL twice daily for treatment or once daily for prophylaxis 1
• Administration with food may improve gastrointestinal tolerability, though this is not required 1, 3, 2

Pediatric Dosing (≥12 months to 12 years)

Weight-based dosing is essential for children, with specific doses determined by body weight rather than age alone. 1, 2

Treatment Dosing (twice daily for 5 days):

• ≤15 kg (≤33 lb): 30 mg twice daily (5 mL oral suspension) 1, 2
• >15-23 kg (>33-51 lb): 45 mg twice daily (7.5 mL oral suspension) 1, 2
• >23-40 kg (>51-88 lb): 60 mg twice daily (10 mL oral suspension) 1, 2
• >40 kg (>88 lb): 75 mg twice daily (12.5 mL oral suspension) 1, 2

Prophylaxis Dosing (once daily for 10 days):

• Same weight-based doses as treatment, but administered once daily instead of twice daily 1, 2
• Duration may extend up to 6 weeks during community outbreaks 1, 2

Infant Dosing (<12 months)

Infants require age-based or weight-based dosing due to developmental differences in drug clearance. 1, 4

Treatment Dosing:

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

Prophylaxis Dosing:

• 3-11 months: 3 mg/kg once daily for 10 days 1, 2
• <3 months: Prophylaxis not recommended unless situation is judged critical due to limited safety data 1

Preterm Infant Dosing

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

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1
• >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1

Renal Impairment Adjustments

Dose reduction is mandatory for patients with moderate to severe renal impairment, as oseltamivir carboxylate accumulates with declining renal function. 1, 2

For Creatinine Clearance 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

End-Stage Renal Disease:

• Oseltamivir is not recommended for patients with end-stage renal disease not undergoing dialysis 2
• Hemodialysis contributes minimally to oseltamivir clearance 1

Formulation and Administration Details

Oseltamivir is available as capsules (30 mg, 45 mg, 75 mg) and oral suspension (6 mg/mL when reconstituted). 1, 3, 2

• Capsules can be opened and contents mixed with liquid if patients cannot swallow whole capsules 1
• If commercial suspension is unavailable, pharmacies can compound a suspension based on package insert instructions to achieve 6 mg/mL concentration 1
• Use an appropriate oral dosing device that accurately measures volume in mL 2
• For infants <1 year, provide a dosing device capable of measuring small volumes accurately 2

Critical Timing Considerations

The 48-hour window from symptom onset is crucial—treatment initiated beyond this timeframe shows significantly reduced efficacy. 1, 3

• For prophylaxis, initiate within 48 hours following close contact with an infected individual 1
• Earlier initiation of therapy is associated with faster symptom resolution 5, 6
• In critically ill ICU patients with H1N1, some benefit may occur when started within 5 days of symptom onset 7

Common Pitfalls and Caveats

Gastrointestinal side effects (nausea, vomiting) occur in approximately 5-15% of patients but are typically mild and transient. 1, 5

• Taking oseltamivir with food significantly reduces GI adverse effects 1, 3
• Do not administer live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use 1
• Avoid LAIV for 14 days after completing oseltamivir therapy 1
• Oseltamivir is not a substitute for annual influenza vaccination 2

Special Populations

Older adults (≥65 years) receive standard dosing unless renal function is impaired—age alone does not require dose adjustment. 1

• The critical factor in elderly patients is creatinine clearance, not chronological age 1
• Immunocompromised patients may continue prophylaxis for up to 12 weeks during community outbreaks 2
• Pregnancy is not a contraindication to oseltamivir use 1
• Patients with chronic cardiac, pulmonary, or other medical conditions can receive standard dosing without contraindication 1, 6