Baloxavir Marboxil

How it works

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

Prescribing in practice

• Effectiveness depends on starting treatment within the first couple of days of symptom onset, so confirm the timing of illness before prescribing.
• Polyvalent cations (such as antacids, oral calcium, magnesium, iron or some supplements) reduce absorption and should be separated in time from the dose.
• Treatment-emergent reduced-susceptibility variants can arise, which is most relevant in immunocompromised or paediatric patients.

Monitoring

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

Counselling the patient

• This medicine works best when taken as early as possible after flu symptoms begin.
• Avoid taking it at the same time as antacids, dairy products or mineral supplements.
• Seek advice if you develop a rash, facial swelling or difficulty breathing.

Evidence & guidelines

Single-dose efficacy in acute uncomplicated influenza was demonstrated in the CAPSTONE randomised controlled trials.