Tamiflu (Oseltamivir) Dosing Guidelines
For adults and adolescents ≥13 years with normal renal function, the standard treatment dose is 75 mg orally twice daily for 5 days, and prophylaxis is 75 mg once daily for 10 days. 1, 2
Adult and Adolescent Dosing (≥13 years)
Treatment:
- 75 mg orally twice daily for 5 days 1, 2
- Must be initiated within 48 hours of symptom onset for maximum benefit (reduces illness duration by 1-1.5 days) 2, 3
- Should not be withheld in high-risk or hospitalized patients presenting beyond 48 hours 3
Prophylaxis:
- 75 mg orally once daily for 10 days after exposure 1, 2
- Should be started within 48 hours of exposure to infected individuals 3
Pediatric Dosing (≥1 year to 12 years)
Weight-based dosing is mandatory for children: 2, 4
Treatment (twice daily for 5 days):
Prophylaxis (once daily for 10 days):
Infant Dosing (<12 months)
Term infants require age-specific dosing: 2, 4
Treatment:
- 9-11 months: 3.5 mg/kg per dose twice daily for 5 days 1, 2
- 0-8 months: 3.0 mg/kg per dose twice daily for 5 days 1, 2
Prophylaxis:
- 3-11 months: 3.0 mg/kg once daily for 10 days 2
- NOT recommended for infants <3 months unless situation is judged critical due to limited safety data 2
Critical Warning for Preterm Infants
Preterm infants require substantially lower doses based on postmenstrual age (gestational age + chronological age) due to immature renal function: 1, 2, 4
- <38 weeks postmenstrual age: 1.0 mg/kg twice daily 1, 2
- 38-40 weeks postmenstrual age: 1.5 mg/kg twice daily 1, 2
- >40 weeks postmenstrual age: 3.0 mg/kg twice daily 1, 2
Never use standard term infant dosing for preterm infants—this leads to drug accumulation and toxicity. 4
Renal Impairment Dosing Adjustments
Dose adjustments are mandatory when creatinine clearance falls below 60 mL/min: 2, 3
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
For pediatric patients with CrCl 10-30 mL/min:
- Reduce the child's weight-based dose to once daily (instead of twice daily) for treatment 4
- For prophylaxis, give half the standard once-daily dose daily, or the full dose every other day 4
Formulation and Administration
- Capsules: 30 mg, 45 mg, 75 mg
- Oral suspension: 6 mg/mL when reconstituted
Oral suspension dosing volumes: 2
- 30 mg dose = 5 mL
- 45 mg dose = 7.5 mL
- 60 mg dose = 10 mL
- 75 mg dose = 12.5 mL
If commercial suspension unavailable: Pharmacies can compound a suspension (final concentration 6 mg/mL) based on package insert instructions 1, 2
Capsules can be opened and mixed with liquid for patients who cannot swallow capsules whole 2
Critical Administration Guidance
Always administer oseltamivir with food to significantly reduce gastrointestinal side effects (nausea and vomiting). 1, 2, 5
- Nausea occurs in approximately 10% and vomiting in 9% of adults receiving oseltamivir 2
- In children, 14.3% experience vomiting compared to 8.5% with placebo 2
- Taking with food significantly reduces severity of these symptoms 2
- Only approximately 1% of patients discontinue due to GI side effects 2
Common Pitfalls to Avoid
Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this leads to underdosing treatment or overdosing prophylaxis. 3
Never use weight-based unit doses (30,45,60,75 mg) intended for children ≥1 year in infants <1 year—these doses are too high. 4
Do not confuse GFR with creatinine clearance when adjusting doses for renal impairment. 4
Never use standard term infant dosing for preterm infants—they have immature renal function and require postmenstrual age-based dosing. 2, 4
Special Populations
Elderly patients (≥65 years): Standard adult dosing (75 mg twice daily for treatment, 75 mg once daily for prophylaxis) unless renal function is impaired 2, 6
Pregnant women: Same dosing as non-pregnant adults (75 mg twice daily for 5 days); pregnancy is not a contraindication 3
Breastfeeding: Not a contraindication to oseltamivir use 3