What is the recommended dose of Xofluza (baloxavir marboxil) for a patient with confirmed or suspected influenza, considering their age and body weight, as well as potential impaired renal function?

Xofluza Dosing for Influenza Treatment and Prophylaxis

Weight-Based Single-Dose Regimen

For patients ≥5 years of age with confirmed or suspected influenza, Xofluza (baloxavir marboxil) is administered as a single oral dose based on body weight: 2 mg/kg for patients <20 kg, 40 mg for patients 20 to <80 kg, and 80 mg for patients ≥80 kg. 1

Specific Dosing by Weight Category

• Patients weighing <20 kg: 2 mg/kg as a single oral dose (oral suspension formulation) 1
• Patients weighing 20 to <80 kg: 40 mg as a single oral dose (one 40 mg tablet or 20 mL oral suspension) 1
• Patients weighing ≥80 kg: 80 mg as a single oral dose (one 80 mg tablet or 40 mL oral suspension) 1

Age Restrictions

• Xofluza is FDA-approved only for patients ≥5 years of age for both treatment and post-exposure prophylaxis 1
• The drug is not indicated for patients <5 years of age due to significantly higher rates of treatment-emergent viral resistance in this younger population 1

Timing of Administration

Xofluza must be administered as soon as possible and within 48 hours of influenza symptom onset for treatment, or within 48 hours following contact with an infected individual for prophylaxis. 1

• The medication may be taken with or without food 1
• Single-dose administration provides a major adherence advantage over multi-day regimens like oseltamivir 2, 3

Prophylaxis Dosing

The prophylaxis dosing is identical to the treatment dosing—the same single weight-based dose is used for both indications. 4, 1

• For patients 40-80 kg: single 40 mg dose 4
• For patients ≥80 kg: single 80 mg dose 4
• Approved for post-exposure prophylaxis in patients ≥5 years of age 4, 1

Renal Impairment Considerations

No dose adjustment is required for patients with impaired renal function when using Xofluza. 1

This represents a significant practical advantage over oseltamivir, which requires mandatory dose reductions for creatinine clearance <60 mL/min 5, 6. The FDA label for baloxavir does not specify any renal dose adjustments, making it particularly useful in elderly patients or those with chronic kidney disease where calculating creatinine clearance and adjusting oseltamivir doses can be cumbersome 1.

Critical Drug Interactions and Administration Pitfalls

Avoid coadministration of Xofluza with dairy products, calcium-fortified beverages, or polyvalent cation-containing products (laxatives, antacids, or oral supplements containing calcium, iron, magnesium, selenium, or zinc). 1, 7

• These products significantly reduce baloxavir absorption and antiviral efficacy 1, 7
• Patients should be counseled to separate Xofluza administration from these products by several hours 7
• This is a common prescribing pitfall that can lead to treatment failure 7

Comparison to Oseltamivir

The evidence demonstrates that baloxavir shows similar efficacy to oseltamivir in time to symptom alleviation but superior viral load reduction at 24 hours post-treatment 8, 9. In the CAPSTONE-2 trial of high-risk patients, median time to symptom improvement was 73.2 hours with baloxavir versus 81.0 hours with oseltamivir (difference not statistically significant), but both were superior to placebo 8. The single-dose regimen offers substantial practical advantages over oseltamivir's twice-daily 5-day course 2, 3.

Resistance Considerations

Treatment-emergent polymerase acidic protein variants with reduced baloxavir susceptibility emerged in approximately 2-10% of treated patients in clinical trials, with higher rates in younger patients. 1, 9

• Variants with I38T/M/F substitutions were observed in 9.7% of baloxavir recipients in the phase 3 CAPSTONE-1 trial 9
• This is the primary reason Xofluza is not approved for patients <5 years of age 1
• Despite resistance emergence, clinical outcomes remained favorable in most cases 8, 9

Safety Profile

Baloxavir demonstrates a favorable safety profile comparable to placebo, with adverse events reported in 20-25% of recipients versus 24-30% in placebo groups. 8, 9

• Most common adverse events include diarrhea, bronchitis, nausea, and headache (each occurring in 1-3% of patients) 1
• In pediatric patients 5 to <12 years, vomiting and diarrhea occurred in 5% each 10
• Serious adverse events are rare and generally not treatment-related 8
• Hypersensitivity reactions including anaphylaxis, angioedema, and urticaria have been reported; discontinue if these occur 1

Special Populations

Elderly patients (≥65 years) receive the same weight-based dosing as younger adults with no age-based adjustments required. 1

The lack of renal dose adjustment requirements makes Xofluza particularly advantageous in elderly populations where renal function commonly declines 1. This contrasts sharply with oseltamivir, which requires careful dose reduction in elderly patients with creatinine clearance <60 mL/min 5, 6.