Oseltamivir Therapeutic Dosing
Adults and Adolescents (≥13 years)
The standard therapeutic dose of oseltamivir is 75 mg orally twice daily for 5 days, initiated within 48 hours of symptom onset. 1, 2, 3
- Treatment should be started as early as possible—ideally within 12–24 hours—because earlier initiation reduces illness duration by an additional 1–3 days compared to treatment begun at 48 hours. 4, 5
- The 5-day course must be completed even if symptoms resolve earlier, to ensure adequate viral suppression and minimize resistance risk. 2
- Taking oseltamivir with food significantly reduces nausea and vomiting (the most common adverse effects, occurring in ~10% of patients) without compromising efficacy. 1, 2, 4
Pediatric Patients (≥12 months to 12 years): Weight-Based Dosing
Children ≥12 months require weight-based dosing administered twice daily for 5 days: 1, 2, 3
| Body Weight | Dose per Administration | Oral Suspension Volume (6 mg/mL) |
|---|---|---|
| ≤15 kg | 30 mg | 5 mL |
| >15–23 kg | 45 mg | 7.5 mL |
| >23–40 kg | 60 mg | 10 mL |
| >40 kg | 75 mg | 12.5 mL |
- Do not round up to the next weight category—a child weighing 15.2 kg receives 30 mg, not 45 mg. 2, 6
- Use a calibrated oral dosing syringe (not household spoons) to measure the suspension accurately. 2, 3
- The oral suspension (6 mg/mL) is the preferred formulation; if unavailable, pharmacies can compound it per package-insert instructions. 1, 2
Infants (3–11 months)
Infants 9–11 months: 3.5 mg/kg per dose twice daily for 5 days. 1, 2, 3
Term infants 0–8 months: 3.0 mg/kg per dose twice daily for 5 days. 1, 2, 3
- Calculate the exact mg/kg dose and measure the corresponding volume of 6 mg/mL suspension using a 3-mL or 5-mL calibrated oral syringe. 2
- Do not use the weight-based categorical dosing (≤15 kg = 30 mg) for infants <12 months—this scheme applies only to children ≥12 months. 2, 6
Preterm Infants: Postmenstrual Age-Based Dosing
Preterm infants require substantially lower doses due to immature renal function: 1, 2
| Postmenstrual Age (PMA) | Dose |
|---|---|
| <38 weeks | 1.0 mg/kg twice daily |
| 38–40 weeks | 1.5 mg/kg twice daily |
| >40 weeks | 3.0 mg/kg twice daily |
- Postmenstrual age = gestational age + chronological age. 2
- Using term-infant dosing for preterm infants can cause toxic drug accumulation. 2
- For extremely preterm infants (<28 weeks PMA), consult a pediatric infectious-disease specialist before initiating therapy. 2, 6
Patients with Moderate Renal Impairment (CrCl 10–30 mL/min)
Treatment dose: 75 mg once daily (instead of twice daily) for 5 days. 1, 2, 3
Alternative treatment dose: 30 mg once daily for 5 days. 1, 2
- Failure to adjust the dose in patients with creatinine clearance <60 mL/min can lead to drug accumulation and toxicity. 2, 7
- Oseltamivir is not recommended for end-stage renal disease patients not undergoing dialysis. 3
Formulation and Administration
- Capsules: Available in 30 mg, 45 mg, and 75 mg strengths. 1, 2
- Oral suspension: Reconstituted to 6 mg/mL concentration; preferred for children and patients unable to swallow capsules. 1, 2, 3
- Capsules may be opened and mixed with sweetened liquid (e.g., simple syrup or Ora-Sweet SF) to achieve a 6 mg/mL concentration if commercial suspension is unavailable. 1, 2
- Administer with or without food, though taking with meals improves gastrointestinal tolerability. 1, 2, 3
Critical Timing and Clinical Pearls
- Initiate treatment within 48 hours of symptom onset for maximum benefit; earlier treatment (within 12–24 hours) provides the greatest reduction in illness duration. 1, 2, 4, 5
- Treatment after 48 hours may still provide benefit in patients with moderate-to-severe or progressive disease and should be strongly considered. 1
- Complete the full 5-day course even if symptoms improve earlier, to ensure adequate viral suppression and prevent resistance. 2
- Gastrointestinal side effects (nausea, vomiting) are mild, transient, and occur in ~10–15% of patients; only ~1% discontinue therapy due to these effects. 2, 4