The U.S. Centers for Disease Control and Prevention has abruptly switched its guidance for use of a drug touted by President Donald Trump as a possible treatment for COVID-19, dropping its reference to anecdotal dosages to say simply that there are no approved drugs for dealing with the disease.

The CDC's online advice for hydroxychloroquine was updated April 7, three days after Reuters reported that the CDC was offering what the news agency called "highly unusual guidance" for the drug's use based on "unattributed anecdotes rather than peer-reviewed science."

The updated, and shortened, guidance says simply that "hydroxychloroquine and chloroquine are under investigation in clinical trials” for use on coronavirus patients and "there are no drugs or other therapeutics approved by the U.S. Food and Drug Administration to prevent or treat COVID-19."

The CDC originally told Reuters that the earlier guidance was crafted for doctors at the request of a White House coronavirus task force, which had urged prompt action.

The CDC did not immediately respond to USA TODAY's queries about the revised guidance.

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Hydroxychloroquine, the anti-malarial drug, was thrust into the spotlight by Trump, who has regularly touted its potential to fight the virus, saying “there are some very strong, powerful signs” of its potential.

Although health experts say that the data on the drug's effectiveness is extremely limited and that more study is needed, Trump said recently that “if it does work, it would be a shame we did not do it early.” He added: “But what do I know? I’m not a doctor.”

As a sign of the president's influence on the issue, Trump noted this week that the federal government had purchased and stockpiled 29 million pills of the drug. “We are sending them to various labs, our military, we’re sending them to the hospitals,” he said.

The question of the drug's effectiveness has divided some key Trump advisers.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, has expressed skepticism over the drug, saying, “The data are really, just, at best, suggestive.”

“There have been cases that show there may be an effect, and there are others to show there's no effect," Fauci said on CBS's "Face the Nation. "So, I think in terms of science, I don't think we could definitively say it works.”

Peter Navarro, the top trade and manufacturing aide to the president who is coordinating the use of the Defense Production Act against the virus for the White House, told CNN's John Berman recently that he believes a "second opinion" is needed about hydroxychloroquine as a treatment.

"I let (Fauci) speak for himself, John, but I would have two words for you: second opinion," Navarro said. "Doctors disagree about things all the time."

According to the CDC, hydroxychloroquine is an arthritis medicine that can also be used as a prevention or treatment of malaria and is used to treat rheumatoid arthritis and lupus. It’s available in the U.S. under prescription only.

The most recent study came from China and found that the anti-malaria drug helped speed the recovery of a small number of patients who were mildly or moderately ill. The study notes that the evidence is limited. Authors of the report said that cough, fever and pneumonia went away faster and that patients’ illnesses were less likely to become severe.

The study was made up of 62 patients where half the subjects were given the usual care and the other half were given the usual care plus hydroxychloroquine.

They were treated for five days, and their fevers and cough were monitored. Pneumonia improved in 25 of the 31 patients who were given the drug vs. 17 patients in the control group. However, authors concluded that more research is needed.

The study was posted on medRxiv before it was accepted by the International Journal of Antimicrobial Agents with limited to no peer review.

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Trump has also cited another small study from France of just a couple dozen patients that found that the drug, combined with common antibiotics, was effective in fighting COVID-19. A subsequent study of 80 patients in France found clinical improvement in all but one.

Other experts criticize the studies' design and lack of information on drug side effects.

“We often see antiviral therapies (that are promising) in the test tube and animal models. But before we give it to patients with confidence, we really need to see the data in humans,” said Jeffrey Klausner, a professor of medicine and public health at the University of California-Los Angeles.

Elisabeth Bik, a microbiologist and scientific integrity consultant who writes the medical blog Science Integrity Digest, says it is "very unusual for the CDC to promote a drug that has no proven ability to cure or prevent a disease."

"The CDC is one of the most reliable sources in this country, and their online information is usually very well curated and trustworthy," Bik says, speculating that the CDC might have initially felt pressure "from high-level leadership."

"So it looks as if the CDC is indeed listening and responding to these concerns by changing their statement and removing the recommended dosages," said Bik, who has challenged the findings of a French study of the drug. "I applaud them for doing the right thing."

Contributing: Adrianna Rodriguez, USA TODAY