How should Xofluza (baloxavir marboxil) be prescribed for patients aged 12 years or older with acute uncomplicated influenza A or B within 48 hours, including dosing, contraindications, and precautions?

Xofluza (Baloxavir Marboxil) Prescribing Guide

Dosing for Patients ≥12 Years Old

Administer Xofluza as a single oral dose within 48 hours of symptom onset for treatment or following exposure for prophylaxis, using weight-based dosing: 40 mg for patients weighing 20 to <80 kg, or 80 mg for patients weighing ≥80 kg. 1

Weight-Based Dosing Table

• 20 kg to <80 kg: One 40 mg tablet 1
• ≥80 kg: One 80 mg tablet 1

Administration Instructions

• Timing is critical: Give as soon as possible within 48 hours of symptom onset for treatment, or following contact with an influenza-infected individual for prophylaxis 1
• Food: May be taken with or without food 1
• Critical drug-food interaction: Avoid concomitant use with dairy products, calcium-fortified beverages, polyvalent cation-containing laxatives, antacids, or oral supplements (calcium, iron, magnesium, selenium, zinc) as these significantly reduce absorption 1

Indications

Treatment

Xofluza is indicated for acute uncomplicated influenza in patients ≥5 years who have been symptomatic for ≤48 hours and are either otherwise healthy or at high risk of complications. 1

The IDSA guidelines recommend starting antiviral treatment as soon as possible for hospitalized patients, those with severe/progressive illness, high-risk patients with chronic conditions, immunocompromised patients, children <2 years, adults ≥65 years, and pregnant/postpartum women 2. While IDSA guidelines primarily recommend neuraminidase inhibitors (oseltamivir, zanamivir, peramivir) 2, baloxavir provides an alternative mechanism of action with single-dose convenience.

Post-Exposure Prophylaxis

Xofluza is indicated for post-exposure prophylaxis in persons ≥5 years following contact with an influenza-infected individual. 1

The 2024 WHO guidelines conditionally recommend baloxavir prophylaxis for anyone exposed to zoonotic influenza and for those exposed to seasonal influenza who are at extremely high risk 3.

Clinical Efficacy

Baloxavir demonstrates superior efficacy to placebo and similar efficacy to oseltamivir for symptom relief, with the added benefit of more rapid viral load reduction. 4, 5

Key Trial Results

• CAPSTONE-2 (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), and 81.0 hours with oseltamivir 4
• CAPSTONE-1 (otherwise healthy patients): Median time to symptom alleviation was 53.7 hours with baloxavir versus 80.2 hours with placebo (p<0.001), similar to oseltamivir 5
• Viral load reduction: Baloxavir achieved greater reductions in viral load at 1 day compared to both placebo and oseltamivir 5
• Transmission prevention: Recent 2025 data showed baloxavir reduced transmission to household contacts by 29% (adjusted incidence 9.5% vs 13.4% placebo, p=0.01) 6

Contraindications

Xofluza is contraindicated in patients with a history of hypersensitivity to baloxavir marboxil or any of its ingredients. 1

Warnings and Precautions

Hypersensitivity Reactions

Initiate appropriate treatment if anaphylaxis, angioedema, urticaria, or erythema multiforme occurs or is suspected. 1

Treatment-Emergent Resistance

Resistance can develop after a single dose, with polymerase acidic protein variants (I38T/M/F substitutions) emerging in approximately 2-10% of treated patients. 5, 7

• The emergence rate was 2.2% in phase 2 trials and 9.7% in phase 3 trials 5
• In high-risk patients (CAPSTONE-2), resistance emerged in 5% of baloxavir recipients 4
• Critical caveat: Xofluza is NOT indicated in patients <5 years due to higher resistance rates in this age group 1
• The 2024 WHO guidelines note concerns about resistance emergence and recommend monitoring drug susceptibility patterns 3

Bacterial Coinfection Risk

Serious bacterial infections may begin with influenza-like symptoms or occur as complications; Xofluza has not been shown to prevent these complications. 1

The IDSA guidelines emphasize investigating and empirically treating bacterial coinfection in patients with severe initial presentation or those who deteriorate after initial improvement 2.

Limitations of Use

Consider available information on drug susceptibility patterns for circulating influenza strains when deciding whether to use Xofluza, as viral factors could diminish clinical benefit. 1

Adverse Events

Baloxavir demonstrates a favorable safety profile comparable to placebo. 4, 5

Common Adverse Events (≥1% in adults/adolescents)

• Diarrhea (3%) 1
• Bronchitis (3%) 1
• Nausea (2%) 1
• Sinusitis (2%) 1
• Headache (1%) 1

Pediatric Patients (5 to <12 years)

• Vomiting (5%) 1, 8
• Diarrhea (5%) 1, 8

In CAPSTONE-2, adverse events occurred in 25% of baloxavir recipients versus 30% of placebo recipients 4. Serious adverse events were rare and mostly unrelated to treatment 4.

Clinical Positioning

Baloxavir offers a single-dose oral regimen that provides similar efficacy to 5-day oseltamivir therapy with more rapid viral clearance, making it particularly valuable for patients where adherence is a concern or rapid viral suppression is desired. 7, 9

The single-dose regimen eliminates adherence concerns inherent to multi-day neuraminidase inhibitor therapy 9. The novel mechanism of action (cap-dependent endonuclease inhibition) provides activity against neuraminidase inhibitor-resistant strains 7, 9. However, the potential for resistance emergence requires ongoing surveillance and consideration of individual patient factors 7.