Common ingredient in cough medicine may help coronavirus grow, study finds

The preliminary findings merit caution and further study, researchers say.
/ Source: TODAY
By A. Pawlowski

A “blueprint” that reveals how the new coronavirus infects human cells and which drugs could impact that process has also led researchers to caution about a common ingredient in cough medicine.

Dextromethorphan — an over-the-counter cough suppressant found in more than 120 cough and cold products — was found to have “pro-viral activity” in lab experiments and “therefore its use should merit caution and further study in the context of COVID-19,” wrote the authors of the study, published in Nature on Thursday.

Since coughing is a key warning sign of the coronavirus infection, that would be extra worrisome for the many people trying to soothe their symptoms with cough syrup or lozenges.

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But the findings don’t necessarily mean people should stop using medicine with this ingredient, said Brian Shoichet, one of the researchers and professor of pharmaceutical chemistry at the University of California, San Francisco.

“I personally wouldn't recommend that based on our data alone. It would stop people from taking almost all cough medications in the U.S. — and many people who would stop won't even have COVID-19,” Shoichet told TODAY. “I do think the pro-viral activity observed in vitro merits further controlled clinical study.”

Nevan Krogan, who led the research and serves as the director of the Quantitative Biosciences Institute at UC San Francisco, agreed.

“This is information we wanted to responsibly report but tempered with a strong caveat that these results were seen in the lab (and) more tests are needed, especially in humans, before any definite conclusions are drawn,” Krogan said.

Dextromethorphan's potential to promote the growth of the virus was observed in monkey cells that were in a lab dish. The effects, if they play out clinically, are likely unique to the new coronavirus and have not been known before, Shoichet noted.

It’s not a known side effect of dextromethorphan and researchers have no reason to believe it would affect influenza, for example, he added.

The study involved more than 120 scientists from the U.S. and Europe who are searching for potential treatments for COVID-19.

They created a blueprint of more than 300 human proteins that the virus requires to infect human cells, then looked at which existing drugs — or those in development — might target those proteins, UCSF said in a news release. They found a number with the potential to treat COVID-19.

Drugs that showed antiviral activity against the new coronavirus in lab experiments included zotatifin, which is currently in clinical trials for cancer; ternatin-4/plitidepsin, which is FDA-approved for the treatment of multiple myeloma; haloperidol, which is used to treat schizophrenia; the antihistamines clemastine and cloperastine; and the female hormone progesterone.

A preclinical compound (a drug not yet approved for any condition and for which there's no human clinical data yet) called PB28 had about 20 times greater antiviral activity in lab experiments than hydroxychloroquine, which is being studied as a potential treatment for COVID-19.

The researchers caution the promising drugs in the analysis have only been tested against the new coronavirus in lab experiments so human clinical trials would be needed to make sure they’re safe and effective. Until then, the authors don’t advocate anyone prescribing or using the drugs to treat COVID-19.

The study “will help to focus clinical trials toward the most promising agents” to combat the virus, Krogan said in a statement.