Xofluza (Baloxavir Marboxil) for Post-Exposure Prophylaxis in Canada
Xofluza is approved for post-exposure prophylaxis at a single weight-based dose (40 mg if <80 kg, 80 mg if ≥80 kg) and must be taken within 48 hours of exposure to an individual with influenza. 1
Dosing for Post-Exposure Prophylaxis
Weight-based single dose administration:
- Patients weighing less than 80 kg: 40 mg as a single oral dose 1
- Patients weighing 80 kg or more: 80 mg as a single oral dose 1
The medication is available as tablets or oral suspension (2 mg/mL after constitution), with the suspension intended for patients unable to swallow tablets or requiring enteral administration 1
Critical Timing Requirements
Xofluza must be administered as soon as possible and within 48 hours following contact with an individual who has influenza. 1 This 48-hour window is absolute—do not administer prophylaxis if more than 48 hours has elapsed since exposure 2, 3. If the window is missed, educate the patient to initiate full-dose empiric treatment immediately if symptoms develop 2, 3.
Who Should Receive Post-Exposure Prophylaxis
Xofluza prophylaxis is indicated for persons 12 years of age and older following contact with an individual who has influenza. 1 However, guidelines emphasize that prophylaxis should be reserved for specific high-risk situations rather than routine use:
- Asymptomatic individuals at very high risk of complications (e.g., severely immunocompromised persons such as hematopoietic stem cell transplant recipients) after household exposure 2, 3
- Unvaccinated household contacts of persons at very high risk of complications from influenza 2, 3
- High-risk children who are unvaccinated, recently vaccinated (within past 2 weeks), or immunocompromised with potentially inadequate vaccine response 2
Important Administration Considerations
Avoid coadministration with dairy products, calcium-fortified beverages, polyvalent cation-containing laxatives, antacids, or oral supplements (calcium, iron, magnesium, selenium, zinc) as these significantly reduce antiviral efficacy 2, 1. Xofluza may be taken with or without food, but timing relative to these interfering substances is critical 1.
Contraindications and Precautions
Do not use Xofluza in:
- Pregnant or breastfeeding women 2, 4
- Severely immunocompromised patients as monotherapy due to concerns about resistance emergence 2, 4
- Patients with known hypersensitivity to baloxavir marboxil (risk of anaphylaxis, angioedema, urticaria, erythema multiforme) 1
Monitoring and Switching to Treatment
If a person receiving prophylaxis develops symptoms, immediately test for influenza and switch to full antiviral treatment dosing, preferably with an antiviral drug with a different resistance profile (such as oseltamivir) 2, 3. This is critical because resistance can emerge with baloxavir exposure 5.
Comparison to Alternative Prophylactic Agents
While Xofluza offers the convenience of a single dose, neuraminidase inhibitors (oseltamivir or zanamivir) remain the primary recommended agents for post-exposure prophylaxis in most guidelines 2, 6, 3. The American Academy of Pediatrics does not specifically recommend baloxavir for routine postexposure prophylaxis in their 2024 guidelines, instead focusing on oseltamivir and zanamivir 4. However, the WHO conditionally recommends baloxavir for prophylaxis in asymptomatic persons at very high risk of hospitalization 7.
Oseltamivir prophylaxis requires 75 mg once daily for 7-10 days after exposure 2, 6, making Xofluza's single-dose regimen potentially advantageous for adherence 8, 9.
Common Pitfalls to Avoid
- Do not use prophylaxis as a substitute for vaccination—influenza vaccine remains the primary prevention method 6, 3
- Do not routinely give prophylaxis to all exposed individuals—reserve for specific high-risk groups outlined above 2, 3
- Do not delay switching to treatment dosing if symptoms develop while on prophylaxis 2, 3
- Do not administer within 2 weeks of live attenuated influenza vaccine as antivirals may affect vaccine efficacy 1
Real-World Evidence
Recent outbreak data demonstrates that baloxavir marboxil can effectively halt influenza transmission when used as post-exposure prophylaxis in closed settings such as college sports teams 10, supporting its practical utility beyond controlled trial settings.