Skip to content
ClinCalc Pro
Menu
Calculators Drugs Pathways AI Dx Donate Get the App
Cap-dependent endonuclease inhibitor (antiviral)

Baloxavir marboxil

Brand names: Xofluza

Baloxavir marboxil is an orally active prodrug antiviral used as a single-dose treatment of uncomplicated influenza A and B, and for post-exposure prophylaxis in eligible contacts.

Dosing — being independently re-sourced

ClinCalc Pro is rebuilding its dose data from primary open sources — the manufacturer SmPC (eMC), the WHO Model Formulary and other official references — under clinician review. This drug's structured dose is not yet published here. Confirm all doses against the product SmPC and your local formulary before prescribing.

Clinical monograph

How it works

Its active metabolite baloxavir inhibits the cap-dependent endonuclease activity of the influenza polymerase acidic protein, blocking viral mRNA synthesis and so halting viral replication.

Prescribing in practice

  • Greatest benefit occurs when started within the first day or two of symptom onset, so confirm timing of illness before prescribing.
  • Avoid co-administration with polyvalent cation-containing products such as antacids, oral magnesium, aluminium, calcium or iron preparations and dairy, as chelation markedly reduces absorption.
  • Treatment-emergent reduced-susceptibility variants can arise, which is relevant in immunocompromised or prolonged illness.

Monitoring

Routine laboratory monitoring is not required; monitor for symptom resolution and watch for rare hypersensitivity reactions.

Counselling the patient

  • This is usually a single oral dose taken as soon as possible after flu symptoms begin.
  • Do not take it at the same time as antacids, dairy, or iron or calcium supplements.
  • Antiviral treatment does not replace annual influenza vaccination.

Evidence & guidelines

The CAPSTONE-1 and CAPSTONE-2 trials demonstrated reduced time to symptom resolution in uncomplicated influenza.

Reference: NICE NG34; UKHSA influenza; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

Calculators
Pathways