What is the recommended oseltamivir (Tamiflu) dosing regimen for post‑exposure prophylaxis in a healthy adult exposed to influenza?

Oseltamivir Post-Exposure Prophylaxis Dosing

For a healthy adult exposed to influenza, the recommended oseltamivir dose is 75 mg once daily for 10 days, initiated as soon as possible and ideally within 48 hours of exposure. 1, 2

Standard Adult Prophylaxis Regimen

• The dose is 75 mg orally once daily (not twice daily) for 10 days following close contact with an infected individual 3, 1, 2
• Initiation should occur within 48 hours of exposure for optimal effectiveness 1
• If more than 48 hours have elapsed since exposure, prophylaxis should not be started; instead, educate the patient to begin full treatment dosing (75 mg twice daily) immediately if symptoms develop 1

Administration Considerations

• Oseltamivir can be taken with or without food, though taking it with food significantly reduces gastrointestinal side effects (nausea/vomiting occur in approximately 10-15% of patients) 3, 4, 5
• The prophylactic dose is once daily, which is half the treatment dose (twice daily)—this is a critical distinction to avoid dosing errors 4

Duration and Efficacy

• The standard duration is 10 days for post-exposure prophylaxis 1, 2
• Protection lasts only as long as the medication is continued; susceptibility to influenza returns when medication is discontinued 6
• Clinical trials demonstrated 67-74% protective efficacy when used for prophylaxis in exposed individuals 7, 8

Important Clinical Pearls

• Oseltamivir prophylaxis is not a substitute for influenza vaccination, which remains the primary prevention strategy 6, 1
• If the patient develops symptoms during prophylaxis, switch immediately to treatment dosing (75 mg twice daily for 5 days) and consider testing for influenza 1
• Prophylaxis does not interfere with antibody response to inactivated influenza vaccine (IIV), so vaccination can be given concurrently if needed 1
• However, live attenuated influenza vaccine (LAIV) effectiveness will be decreased in patients receiving oseltamivir, so timing considerations are needed for the nasal spray vaccine 6

Special Situations

• For immunocompromised patients, prophylaxis may be extended up to 12 weeks during community outbreaks 2
• Pregnant women receive the same dosing as non-pregnant adults (75 mg once daily for prophylaxis) 4
• No dose adjustment is needed based on age alone for elderly patients, but renal function must be assessed 4

Renal Impairment Adjustments

• If creatinine clearance is 10-30 mL/min, reduce the dose to 30 mg once daily or 75 mg every other day for 10 days 3, 4
• No adjustment is needed for creatinine clearance ≥30 mL/min 3

Common Pitfall to Avoid

Do not confuse prophylaxis dosing (once daily) with treatment dosing (twice daily)—this is the most common prescribing error and can lead to either underdosing treatment or overdosing prophylaxis 4