Baloxavir marboxil, a cap-dependent endonuclease inhibitor, was approved in Japan on 23 February 2018 for the treatment of influenza A and B virus infections, making Japan the first country to authorise its clinical use. On 27 November 2020, its indication was expanded to include prophylactic use for household members or cohabitants of influenza patients who are at high risk of severe disease. For patients aged?≥?12 years, the approved dose is 80 mg for those weighing?>?80 kg, and 40 mg for those weighing?≤?80 kg. For patients aged?