Prophylactic Use of Tamiflu (Oseltamivir)
For post-exposure prophylaxis, adults and adolescents ≥13 years should receive oseltamivir 75 mg once daily for 10 days, initiated within 48 hours of exposure to a confirmed or suspected influenza case. 1, 2, 3
Standard Prophylaxis Regimens
Adults and Adolescents (≥13 years)
- Post-exposure prophylaxis: 75 mg once daily for 10 days following close contact with an infected individual 1, 2, 4
- Community outbreak/seasonal prophylaxis: 75 mg once daily for up to 6 weeks during periods of local influenza activity 4, 5, 6
- Initiate within 48 hours of exposure for maximum effectiveness 3, 7
Pediatric Patients (≥1 year)
- Weight-based dosing (once daily for 10 days): 1, 2, 7
- ≤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
- Community outbreak: Same doses once daily for up to 6 weeks 4
Infants (3-11 months)
- Dose: 3 mg/kg once daily for 10 days 1, 2, 7
- Critical limitation: Prophylaxis is not recommended for infants <3 months unless the situation is judged critical due to limited safety data 2, 7
Preterm Infants
- Prophylaxis dosing for preterm infants is not established in the guidelines 1
- Treatment dosing exists but prophylaxis use requires careful risk-benefit assessment 1
Key Clinical Indications for Prophylaxis
High-priority populations for prophylaxis include: 7, 8
- High-risk individuals who have not yet received influenza vaccination
- High-risk individuals during the 2-week period after vaccination (before full immunity develops)
- Unimmunized family members and healthcare workers with close contact to high-risk unimmunized children or infants <6 months
- Control of influenza outbreaks in institutional settings with unimmunized staff and residents
- Adjunctive prophylaxis in vaccinated high-risk elderly patients during outbreaks 5, 6
High-risk conditions warranting prophylaxis consideration include: 7
- Chronic cardiac or pulmonary disease (including asthma)
- Diabetes mellitus
- Immunodeficiency or immunosuppression
- Pregnancy
- Age <2 years or ≥65 years
Renal Impairment Adjustments
Creatinine Clearance 30-60 mL/min
- Reduce to 30 mg once daily 4
Creatinine Clearance 10-30 mL/min
- Option 1: 30 mg once daily for 10 days 1, 2, 4
- Option 2: 75 mg every other day for 10 days (5 total doses) 1, 2, 7
End-Stage Renal Disease (ESRD)
- On hemodialysis: 30 mg immediately, then 30 mg after alternate hemodialysis cycles for recommended prophylaxis duration 4
- On CAPD: 30 mg immediately, then 30 mg once weekly for recommended prophylaxis duration 4
- Not on dialysis: Not recommended 1, 4
Formulation and Administration
Available Forms
- Capsules: 30 mg, 45 mg, 75 mg 1, 7, 4
- Oral suspension: 6 mg/mL concentration when reconstituted 1, 2, 7
Suspension Dosing Volumes (for 6 mg/mL concentration)
Administration Tips
- Can be taken with or without food 1, 4
- Taking with meals may reduce gastrointestinal side effects (nausea, vomiting) 1, 2, 3
- Capsules can be opened and mixed with liquid if swallowing is difficult 2, 3
- If commercial suspension unavailable, pharmacies can compound using package instructions 1, 2
Critical Drug Interactions
Live Attenuated Influenza Vaccine (LAIV): 1, 2, 7
- Avoid LAIV within 48 hours before oseltamivir use
- Do not use oseltamivir for 14 days after LAIV administration (unless medically indicated)
- Oseltamivir may interfere with LAIV vaccine efficacy 3
- This interaction does not apply to inactivated influenza vaccines
Common Pitfalls and How to Avoid Them
Timing Errors
- Do not delay initiation waiting for laboratory confirmation of influenza in the index case 3, 7
- Start prophylaxis based on clinical suspicion if within the 48-hour window after exposure 3, 7
- Rapid antigen tests have poor sensitivity and should not delay treatment decisions 7
Dosing Confusion
- Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily) - this is a common prescribing error 3
- Prophylaxis duration is 10 days for post-exposure, not 5 days 1, 2, 4
Inappropriate Use
- Prophylaxis is not a substitute for annual influenza vaccination 4
- Consider available information on local influenza drug susceptibility patterns before prescribing 4
- Vaccination remains the best option for preventing influenza; reserve prophylaxis for select high-risk situations 9
Special Population Considerations
- Pregnancy: Use same dosing as non-pregnant adults; pregnancy substantially increases risk of severe influenza complications 7
- Breastfeeding: Not a contraindication to oseltamivir use 7
- Elderly with multiple medications: Well tolerated even with significant concomitant medications 6
Adverse Effects
Most common (>1% and more common than placebo): 4
- Nausea
- Vomiting
- Headache
- Pain (in prophylaxis studies)
Gastrointestinal effects are typically mild and transient 5
Neuropsychiatric events: Patients with influenza, particularly pediatric patients, may be at increased risk of confusion or abnormal behavior early in illness; monitor for signs of abnormal behavior 4
Serious skin/hypersensitivity reactions: Discontinue immediately if Stevens-Johnson Syndrome, toxic epidermal necrolysis, or erythema multiforme occur 4
Evidence for Prophylaxis Efficacy
Post-exposure household prophylaxis: Oseltamivir 75 mg once daily for 7 days significantly reduces risk of illness in household contacts when administered within 48 hours of symptom onset in the infected person 5
Seasonal prophylaxis in vaccinated elderly: 92% protective efficacy demonstrated in frail older subjects (mean age 81 years) receiving 75 mg once daily for 6 weeks, with 91% efficacy specifically in vaccinated individuals 6
Community outbreak prophylaxis: >70% prevention of naturally acquired influenza in unvaccinated otherwise healthy adults receiving 75 mg once or twice daily for 6 weeks during local influenza activity 5