Adult Oseltamivir (Tamiflu) Dosing
The standard adult dose of oseltamivir is 75 mg orally twice daily for 5 days for treatment and 75 mg once daily for 10 days for post-exposure prophylaxis, with mandatory dose reductions required for moderate-to-severe renal impairment (creatinine clearance ≤60 mL/min). 1, 2, 3
Standard Treatment Dosing
- Adults and adolescents ≥13 years: 75 mg orally twice daily for 5 days. 1, 2, 3
- Treatment should be initiated within 48 hours of symptom onset for maximum benefit, reducing illness duration by 1–1.5 days. 2, 4, 5
- Earlier initiation yields greater benefit: Starting within 12 hours reduces illness duration by an additional 74.6 hours compared to starting at 48 hours; starting within 24 hours provides an additional 53.9 hours of benefit. 4
- Complete the full 5-day course even if symptoms improve earlier—early discontinuation increases resistance risk and is not supported for neuraminidase inhibitors. 2
Post-Exposure Prophylaxis Dosing
- Adults and adolescents ≥13 years: 75 mg orally once daily for 10 days following close contact with an infected individual. 2, 3, 5
- Prophylaxis should be started within 48 hours of exposure to infected individuals. 2
- For seasonal prophylaxis during community outbreaks, 75 mg once daily can be continued for up to 6 weeks (or up to 12 weeks in immunocompromised patients). 3
Renal Impairment Dose Adjustments
Dose modifications are mandatory for creatinine clearance ≤60 mL/min to prevent drug accumulation. 2, 6, 3
| Creatinine Clearance | Treatment Dose | Prophylaxis Dose |
|---|---|---|
| >60–90 mL/min | 75 mg twice daily × 5 days | 75 mg once daily |
| >30–60 mL/min (moderate) | 30 mg twice daily × 5 days | 30 mg once daily |
| >10–30 mL/min (severe) | 30 mg once daily × 5 days | 30 mg every other day |
| ESRD on hemodialysis | 30 mg immediately, then 30 mg after each dialysis cycle (max 5 days) | 30 mg immediately, then 30 mg after alternate dialysis cycles |
| ESRD on CAPD | Single 30 mg dose immediately | 30 mg immediately, then 30 mg once weekly |
| ESRD not on dialysis | Not recommended | Not recommended |
Special Populations
Elderly Patients (≥65 years)
- No dose reduction is required based on age alone—standard adult dosing (75 mg twice daily) applies. 2, 7
- However, renal function must be assessed as it declines with aging, and dose adjustments are mandatory if creatinine clearance falls below 60 mL/min. 2, 7
Pregnant Women
- Pregnant women receive the same dosing as non-pregnant adults: 75 mg twice daily for 5 days. 2, 7
- Breastfeeding is not a contraindication to oseltamivir use. 2, 7
Immunocompromised Patients
- Patients who are immunocompromised or unable to mount an adequate febrile response (e.g., very elderly) should receive oseltamivir treatment regardless of time elapsed since symptom onset. 1, 2
- Hospitalized patients who are severely ill, particularly if immunocompromised, may benefit from antiviral treatment started more than 48 hours from disease onset, although evidence is limited. 1
Administration Considerations
- Take with food to significantly reduce gastrointestinal side effects (nausea and vomiting), which occur in approximately 10–15% of patients. 2, 6, 4, 5
- Nausea and vomiting are typically mild, transient, and resolve within 1–2 days. 4, 8
- Only approximately 1% of patients discontinue oseltamivir due to gastrointestinal side effects. 2
Formulation
- Available as 30 mg, 45 mg, and 75 mg capsules. 6, 3
- Oral suspension: 6 mg/mL concentration when reconstituted from powder. 6, 3
- For the 75 mg dose using oral suspension: 12.5 mL of the 6 mg/mL suspension. 2, 6
- Capsules can be opened and contents mixed with liquid if patients cannot swallow capsules whole. 6
Critical Pitfalls to Avoid
- Do not confuse treatment dosing (twice daily) with prophylaxis dosing (once daily)—this leads to underdosing treatment or overdosing prophylaxis. 2, 7
- Do not withhold treatment in high-risk or hospitalized patients presenting beyond 48 hours—these patients may still benefit, particularly if severely ill. 1, 2
- Do not skip renal dose adjustments—failure to reduce doses in renal impairment leads to toxic drug accumulation. 2, 6, 3
- Do not stop therapy early even if symptoms resolve before day 5—completing the full course prevents resistance. 2