A research team has confirmed in animal testing that mutated influenza viruses resistant to baloxavir marboxil, an antiflu drug sold as Xofluza, can cause infections and symptoms to a degree comparable to regular influenza viruses.
The team, led by University of Tokyo professor Yoshihiro Kawaoka, published the results of their study in the online edition of British science magazine Nature Microbiology on Tuesday.
The team examined viruses obtained from 38 influenza patients last winter before and after treatment with Xofluza. Resistant viruses were found in nine patients who were administered the drug.
The study shows that hamsters and ferrets experimentally infected with the resistant viruses lost weight and passed the infection to animals in adjacent cages, the same phenomenon that is seen among animals infected with regular flu viruses.
The results suggest the possibility of person-to-person transmission of the resistant viruses, the team said in the report.
Released in spring last year, Xofluza has been used widely as a one-dose oral medication for influenza, even though its mutability was reported in clinical trials.
The Japanese Association of Infectious Diseases has suggested caution in use of the drug for children under 12 years old, who are at high risk from drug-resistant viruses due to their lower levels of immunity.