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US warns monkey smallpox could mutate to become resistant to antiviral drugs

WASHINGTON –

US health officials are warning of the misuse of the only drug available to treat smallpox in monkeys, saying even a small mutation in the virus can make it ineffective.

The Food and Drug Administration updated guidance this week for Tpoxx, which has been prescribed to tens of thousands of patients with the virus.

In an online update, FDA officials warned that a single molecular change to monkeypox “could greatly affect the antiviral activity of Tpoxx.” As the virus is constantly evolving to overcome obstacles to infection, including drugs, regulators insist that doctors should be “cautious” in prescribing drugs.

The call to scale down use of Tpoxx follows weeks of criticism from HIV advocates and other patient groups, who have urged the Biden administration to make the antiretroviral drug more widely available. Tpoxx is approved for the related smallpox virus, and its use against monkeypox is considered experimental and tightly controlled by federal officials.

Physicians who wish to prescribe medication must submit a form to the Centers for Disease Control and Prevention, document their patient’s needs, and agree to monitor their results and any side effects. Officials shipped 37,000 courses of medication to doctors.

Tpoxx works by targeting a unique protein found in monkeypox, smallpox, and similar viruses. The FDA said this week that numerous laboratory, animal and human reports suggest multiple ways in which smallpox in monkeys can develop resistance to the therapy.

The update comes as federal officials on Thursday expressed cautious optimism about the trajectory of the outbreak, noting that new cases have fallen about 50% since their peak in August. .

During a briefing at the White House, CDC Director Dr. Rochelle Walensky suggested that the decline in vaccinations, access to education and individuals reduces the behaviors associated with contagion. The majority of cases in the US are in men who have sex with men, although officials stress that the virus can infect anyone.

Dr. Anthony Fauci, the nation’s top infectious disease official, noted that drug resistance is always a risk when using antiviral drugs.

“That’s why we’re uncomfortable when you only have a single drug,” Fauci told reporters. He added that a recently released study of Tpoxx supported by the National Institutes of Health will monitor for markers of mutations that can lead to drug resistance. The study is expected to enroll more than 500 patients across 60 US sites.

Last month, the Biden administration invoked rare emergency powers to prolong the nation’s limited supply of monkeypox vaccine. And last week, a separate statement promoted the use of experimental tests for the virus.

But no changes were made to allow emergency use of Tpoxx, prompting complaints from groups representing gay and bisexual people.

The US government’s national stockpile contains more than 1.7 million Tpoxx keys, originally manufactured for use in a potential bioterrorism attack.

The FDA approved the drug in 2018 under an “animal rule,” which allows for approval based on animal data when human testing is unethical or unfeasible. Smallpox was declared eradicated by the World Health Organization in 1980, ruling out the possibility for human studies.

Although this drug has been approved for smallpox, its effectiveness has been measured in monkeys infected with smallpox, which is considered a reasonably predictive marker of the effect of smallpox. season for humans. Animals receiving Tpoxx survived at a higher rate than animals receiving placebo. But FDA officials have warned that the animal results must be confirmed in human testing.

“Without human trials, we don’t know if Tpoxx would benefit people with monkeypox,” FDA commissioner Dr. Robert Califf told Senate lawmakers at a hearing this week. this.

The CDC reported last week that 3.5% of patients monitored through their Tpoxx program reported side effects, mainly headaches and nausea.

The agency has only received back about 200 forms from doctors documenting a patient’s initial symptoms and outcomes, representing less than 1% of the doses shipped since the start of the outbreak.

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Stobbe reports from New York


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The Associated Press Health and Science Division receives support from the Howard Hughes Medical Institute’s Science Education Department. AP is solely responsible for all content.

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