FDA warns monkeypox could mutate if antiviral drug is overused

The monkeypox virus is only one mutation away from evading a key antiviral drug being used to treat at-risk patients, federal health officials are now warning — and they're urging doctors to be "judicious" in prescribing the sought-after treatment. 

The new FDA guidance for the antiviral drug known as tecovirimat, or Tpoxx, was published this week online and in updated labeling. 

The regulator says lab and animal studies, and evidence from a human case of this family of viruses, suggest monkeypox has "several genetic pathways" to evolve resistance to tecovirimat. Many "require only a single amino acid change," the FDA said.