What is the recommended dosing of oseltamivir (Tamiflu) for treatment and prophylaxis in adults, children, patients with renal impairment, and pregnant or breastfeeding women?

Oseltamivir (Tamiflu) Dosing Recommendations

Adult and Adolescent Dosing (≥13 years)

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 treatment initiation within 48 hours of symptom onset for maximum benefit. 1, 2, 3

• Administration with meals significantly reduces gastrointestinal side effects (nausea and vomiting occur in approximately 10-15% of patients), though food is not required for absorption 1, 2
• Treatment duration is 5 days for acute influenza 3
• Prophylaxis duration is 10 days for post-exposure prophylaxis and up to 6 weeks for seasonal/community outbreak prophylaxis 3
• In immunocompromised patients, prophylaxis may be extended up to 12 weeks 3

Pediatric Dosing (1-12 years)

Weight-based dosing is mandatory for children 1-12 years, with treatment given twice daily for 5 days and prophylaxis once daily for 10 days. 4, 1, 3

Treatment Dosing (twice daily for 5 days):

• ≤15 kg (≤33 lb): 30 mg twice daily 4, 3
• >15-23 kg (>33-51 lb): 45 mg twice daily 4, 3
• >23-40 kg (>51-88 lb): 60 mg twice daily 4, 3
• >40 kg (>88 lb): 75 mg twice daily 4, 3

Prophylaxis Dosing (once daily for 10 days):

• Same weight-based doses as treatment, but given once daily instead of twice daily 4, 3

Infant Dosing (<1 year)

For term infants 2 weeks to <1 year, the treatment dose is 3 mg/kg per dose twice daily for 5 days. 1, 5, 3

• Age 0-8 months: 3 mg/kg twice daily for treatment 1, 5
• Age 9-11 months: 3.5 mg/kg twice daily for treatment 1, 5
• Prophylaxis in infants 3-8 months: 3 mg/kg once daily for 10 days 5
• Prophylaxis NOT recommended for infants <3 months unless the situation is judged critical due to limited safety data 4, 2

Critical Warning for Preterm Infants:

Never use the standard 3 mg/kg term infant dosing for preterm infants—this leads to toxic drug concentrations due to immature renal function. 4, 5

• Preterm infants <38 weeks postmenstrual age (PMA): 1.0 mg/kg twice daily 5
• Preterm infants 38-40 weeks PMA: 1.5 mg/kg twice daily 5
• Preterm infants >40 weeks PMA: 3.0 mg/kg twice daily 5

Renal Impairment Dosing Adjustments

Dose reductions are mandatory when creatinine clearance falls below 60 mL/min. 1, 2, 3

Treatment Dosing:

• CrCl 30-60 mL/min: 75 mg once daily (instead of twice daily) for 5 days 3
• CrCl 10-30 mL/min: 30 mg once daily for 5 days 4, 3
• End-stage renal disease not on dialysis: Oseltamivir is NOT recommended 3

Prophylaxis Dosing:

• CrCl 10-30 mL/min: 30 mg once daily OR 75 mg every other day for 10 days (5 total doses) 4, 1

Pediatric Renal Impairment:

• For children with CrCl 10-30 mL/min, reduce the weight-based dose to once daily (instead of twice daily) for treatment 5
• For prophylaxis, give half the standard once-daily dose daily, or the full once-daily dose every other day 5

Important caveat: Current renal dosing recommendations may result in subtherapeutic concentrations early in infection for patients with mild-to-moderate renal impairment (CrCl 30-90 mL/min), as these recommendations focus on steady-state rather than early therapeutic concentrations 6. Consider using the full 75 mg first dose followed by reduced subsequent doses, with therapeutic drug monitoring if available 6.

Pregnancy and Breastfeeding

Pregnant women receive the same dosing as non-pregnant adults: 75 mg twice daily for 5 days for treatment, and breastfeeding is not a contraindication to oseltamivir use. 1, 2

Critical Timing Considerations

Treatment must be initiated within 48 hours of symptom onset for maximum benefit—earlier initiation (within 12-24 hours) provides substantially greater benefit, reducing illness duration by up to 3.1 days compared to initiation at 48 hours. 2, 7, 8

• Prophylaxis should be started within 48 hours of exposure to infected individuals 1
• Treatment within 12 hours reduces illness duration by an additional 74.6 hours compared to treatment at 48 hours 8
• Treatment within 24 hours reduces illness duration by an additional 53.9 hours compared to treatment at 48 hours 8

Formulation Details

• Capsules: Available as 30 mg, 45 mg, and 75 mg 1, 3
• Oral suspension: 6 mg/mL when reconstituted from powder (preferred for patients who cannot swallow capsules) 1, 3
• For infants <1 year, use an appropriate measuring device (3 mL or 5 mL oral syringe) instead of the standard syringe supplied 1

Common Pitfalls to Avoid

• Never confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this leads to underdosing treatment or overdosing prophylaxis 1, 2
• Never use term infant dosing (3 mg/kg) for preterm infants—this causes toxic drug concentrations 4, 5
• 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 5
• Do not overlook renal function assessment in elderly patients—age alone does not require dose reduction, but declining renal function with age mandates dose adjustment when CrCl <60 mL/min 1
• Patients with larger body mass (obesity) may require higher initial doses to achieve therapeutic concentrations early in infection, though standard dosing recommendations do not account for this 6