Although a new fast-acting flu drug decreased the time people were sick with flu symptoms by just over a day, two clinical trials found viral resistance could develop rapidly to the drug, STAT reports.
The drug, baloxavir marboxil, significantly reduced the number of viruses patients with infections had in their upper respiratory tracts, which suggests they may not be as likely to infect others through coughs and sneezes.
But the single-dose drug failed to make patients feel better faster than oseltamivir, or Tamiflu.
The findings of the studies, published recently in the New England Journal of Medicine, raised concern about viral resistance developing rapidly to the drug. Virus samples from about 10 percent of people treated in one of the clinical trials showed mutations believed to let viruses evade the effect of the drug.
Despite this finding, there is still hope for baloxavir, and the FDA is giving it a priority review. The agency said it would rule on the drug by the end of the year.