What is the recommended dosing for Xofluza (baloxavir marboxil) in the treatment of influenza A and B?

Xofluza Dosing for Influenza Treatment and Prophylaxis

Xofluza (baloxavir marboxil) is administered as a single weight-based oral dose: 40 mg for patients weighing 40 to <80 kg, and 80 mg for patients weighing ≥80 kg, for both treatment and prophylaxis of influenza A and B. 1

Patient Eligibility

• Xofluza is FDA-approved for patients ≥12 years of age weighing at least 40 kg for treatment of acute uncomplicated influenza 1, 2, 3
• For prophylaxis (post-exposure), the same age and weight restrictions apply: ≥12 years and >40 kg 4
• The medication is also approved for patients ≥5 years of age, with specific dosing for those weighing <20 kg using the oral suspension formulation 1

Weight-Based Dosing Regimen

For Patients ≥5 Years Using Tablets or Suspension:

Patients weighing 20 kg to <80 kg:

• Single dose of 40 mg (one 40 mg tablet OR 20 mL of oral suspension) 1

Patients weighing ≥80 kg:

• Single dose of 80 mg (one 80 mg tablet OR 40 mL of oral suspension, requiring two bottles) 1

Pediatric patients <20 kg (≥5 years):

• 2 mg/kg as a single dose using oral suspension 1

Prophylaxis Dosing:

The prophylaxis dosing is identical to treatment dosing—same single weight-based dose 4:

• 40 mg for patients 40-80 kg 4
• 80 mg for patients ≥80 kg 4

Timing and Administration

• Administer as soon as possible within 48 hours of symptom onset for treatment 1, 2, 3
• For prophylaxis, administer following contact with an individual who has influenza 1
• May be taken with or without food 1

Critical Administration Caveat:

Avoid coadministration with dairy products, calcium-fortified beverages, polyvalent cation-containing laxatives, antacids, or oral supplements (calcium, iron, magnesium, selenium, zinc) 1. These significantly reduce baloxavir absorption and efficacy.

Oral Suspension Preparation (When Tablets Cannot Be Used)

• Constitute with 20 mL of drinking water or sterile water at time of dispensing 1
• Must be administered within 10 hours after constitution (no preservative) 1
• Use measuring device (oral syringe) to ensure accurate dosing 1
• Can be used for enteral administration via feeding tube with 1 mL water flush before and after 1

Renal and Hepatic Impairment

No dosage adjustment is needed for mild-to-moderate hepatic or renal impairment 3. This represents a significant practical advantage over oseltamivir, which requires complex dose reductions for creatinine clearance <30 mL/min 5.

Clinical Efficacy Context

• Baloxavir demonstrates similar time to symptom alleviation compared to oseltamivir but with significantly faster viral load reduction within 24 hours 6, 7, 8
• In high-risk patients, median time to symptom improvement was 73.2 hours with baloxavir versus 102.3 hours with placebo (29.1 hour difference, p<0.0001) 8
• The single-dose regimen offers superior adherence compared to oseltamivir's 5-day twice-daily course 6, 2

Safety Profile

Common adverse events include diarrhea, bronchitis, nausea, nasopharyngitis, and headache, with safety comparable to placebo 1, 8. Serious adverse events are rare and similar across treatment groups 8.

Resistance Monitoring Consideration

Emergence of polymerase acidic protein variants with reduced baloxavir susceptibility (Ile38 substitutions) occurred in approximately 5% of treated patients 8. While human-to-human transmission of resistant variants has been documented, this does not currently alter dosing recommendations but emphasizes the importance of appropriate patient selection 6.