Prophylactic Oseltamivir Dosing
For healthy adults and adolescents ≥13 years, the standard prophylactic dose of oseltamivir is 75 mg orally once daily for 10 days following exposure to influenza. 1
Adult and Adolescent Prophylaxis (≥13 years)
- Standard dose: 75 mg orally once daily for 10 days after close contact with an infected individual. 1, 2
- Prophylaxis should be initiated within 48 hours of exposure to maximize effectiveness. 1
- No dose reduction is necessary based on age alone in elderly patients (≥65 years), but renal function must be assessed as it declines with aging. 1
Pediatric Prophylaxis (1–12 years)
Weight-based dosing is required for children, administered once daily for 10 days: 1, 3
- ≤15 kg (≤33 lb): 30 mg once daily
- >15–23 kg (>33–51 lb): 45 mg once daily
- >23–40 kg (>51–88 lb): 60 mg once daily
- >40 kg (>88 lb): 75 mg once daily
These doses mirror the treatment weight categories but are given once daily instead of twice daily. 1
Infant Prophylaxis (3–11 months)
- Infants 3–11 months: 3 mg/kg orally once daily for 10 days. 1, 2
- Infants <3 months: Prophylaxis is NOT recommended unless the clinical situation is judged critical, due to limited safety and efficacy data. 1, 2
Renal Impairment Adjustments
For patients with creatinine clearance 10–30 mL/min (moderate renal impairment), dose reduction is mandatory: 1, 2
- Option 1: 30 mg orally once daily for 10 days
- Option 2: 75 mg orally every other day for 10 days (total of 5 doses)
The most important consideration in older adults is renal function, not age—dose reductions are mandatory when creatinine clearance falls below 60 mL/min. 2
Alternative Prophylaxis Options
If oseltamivir cannot be used, zanamivir is an alternative neuraminidase inhibitor for prophylaxis: 4
- Zanamivir is administered via inhalation (two 5-mg inhalations once daily)
- However, zanamivir is generally not recommended for patients with underlying airway disease (asthma, COPD) due to risk of bronchospasm. 4
- Patients with asthma or COPD should have a fast-acting inhaled bronchodilator available if zanamivir is used. 4
Administration Guidance
- Take with food: Administration with meals significantly reduces gastrointestinal side effects (nausea and vomiting), which occur in approximately 10–15% of patients. 1, 2
- Formulation: Available as 30 mg, 45 mg, and 75 mg capsules, or as oral suspension (6 mg/mL when reconstituted). 1
- For pediatric patients requiring liquid formulation, the oral suspension volumes are: 30 mg = 5 mL, 45 mg = 7.5 mL, 60 mg = 10 mL, 75 mg = 12.5 mL. 2
Common Pitfalls to Avoid
- Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this can lead to underdosing treatment or overdosing prophylaxis. 1
- Do not use term infant dosing (3 mg/kg) for preterm infants—this leads to toxic drug concentrations due to immature renal function. 1, 2
- Do not overlook renal function assessment in elderly patients—age alone does not require dose reduction, but declining renal function does. 1, 2
- Do not use weight-based categorical dosing (≤15 kg = 30 mg) for infants under 12 months—that scheme applies only to children ≥12 months. 2