What is the appropriate Tamiflu (Oseltamivir) dosing regimen for patients with and without Impaired renal function, across different age and weight groups?

Tamiflu (Oseltamivir) Dosing Guidelines

Standard Adult and Adolescent Dosing (≥13 years)

For adults and adolescents with normal renal function, administer 75 mg twice daily for 5 days for treatment, or 75 mg once daily for 10 days for prophylaxis. 1, 2

• Treatment must be initiated within 48 hours of symptom onset for maximum effectiveness 1, 3
• For prophylaxis, initiate within 48 hours of exposure to an infected individual 1
• During community outbreaks, prophylaxis can be extended up to 6 weeks at 75 mg once daily 2

Pediatric Dosing by Age and Weight

Children ≥1 year to 12 years (Weight-Based)

Use weight-based dosing for all children in this age group, administered twice daily for treatment or once daily for prophylaxis: 1, 4

• ≤15 kg (≤33 lb): 30 mg per dose 1
• >15-23 kg (>33-51 lb): 45 mg per dose 1
• >23-40 kg (>51-88 lb): 60 mg per dose 1
• >40 kg (>88 lb): 75 mg per dose 1

Treatment duration is 5 days; prophylaxis duration is 10 days (or up to 6 weeks during community outbreaks) 1, 2

Infants 9-11 months

Administer 3.5 mg/kg per dose twice daily for 5 days for treatment. 1, 4

• For prophylaxis: 3.5 mg/kg once daily for 10 days 1

Term Infants 0-8 months

Administer 3 mg/kg per dose twice daily for 5 days for treatment. 1, 4, 2

• For prophylaxis in infants 3-8 months: 3 mg/kg once daily for 10 days 1, 4
• Prophylaxis is NOT recommended for infants <3 months unless the situation is judged critical due to limited safety data 1, 4

Preterm Infants (Critical Distinction)

Never use standard term infant dosing for preterm infants—they require substantially lower doses based on postmenstrual age (gestational age + chronological age) due to immature renal function: 1, 4

• <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1, 4
• 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1, 4
• >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1, 4

Renal Impairment Dosing Adjustments

Creatinine Clearance >30 to 60 mL/min

Reduce treatment dose to 30 mg twice daily for 5 days. 2

• For prophylaxis: 30 mg once daily 2

Creatinine Clearance 10-30 mL/min (Moderate to Severe Impairment)

Reduce treatment dose to 30 mg once daily for 5 days. 1, 2

• For prophylaxis: 30 mg once daily OR 75 mg every other day for 10 days (5 total doses) 1, 2

End-Stage Renal Disease (ESRD) on Hemodialysis

Administer 30 mg immediately, then 30 mg after every hemodialysis cycle, not to exceed 5 days of treatment. 2

• For prophylaxis: 30 mg immediately, then 30 mg after alternate hemodialysis cycles for the recommended duration 2

ESRD on Continuous Ambulatory Peritoneal Dialysis (CAPD)

Administer a single 30 mg dose immediately for treatment. 2

• For prophylaxis: 30 mg immediately, then 30 mg once weekly for the recommended duration 2

Formulation and Administration

Oseltamivir is available as 30 mg, 45 mg, and 75 mg capsules, and as oral suspension (6 mg/mL when reconstituted). 1, 4

Oral Suspension Volumes (6 mg/mL concentration):

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

Alternative Administration:

• Capsules can be opened and contents mixed with liquid if patients cannot swallow whole 1
• If commercial suspension unavailable, pharmacies can compound suspension per package insert instructions 1

Administration Recommendations to Improve Tolerability

Administer oseltamivir with food to significantly reduce nausea and vomiting, which occur in approximately 10-15% of patients. 1, 3, 5

• Gastrointestinal effects are typically mild and transient 1, 3
• Only approximately 1% of patients discontinue due to GI side effects 1

Critical Drug Interaction

Avoid live attenuated influenza vaccine (LAIV) within 48 hours before oseltamivir use, and do not use oseltamivir for 14 days after LAIV vaccination, as it may interfere with vaccine efficacy. 1, 3

Common Pitfalls to Avoid

• Never wait for laboratory confirmation before initiating treatment in patients with influenza-like illness during local influenza activity—start empirically 1, 3
• Never use weight-based dosing intended for children ≥1 year (30,45,60,75 mg unit doses) in infants <1 year—these doses are too high 4
• Never confuse creatinine clearance with GFR when dosing for renal impairment 4
• Never use standard term infant dosing for preterm infants—they require postmenstrual age-based dosing 1, 4
• In elderly patients (≥65 years), the most important consideration is renal function, not age—dose reductions are mandatory when creatinine clearance falls below 60 mL/min 1