The governor of Osaka Prefecture touted the powers of gargling medicine to control the coronavirus and recommended its use, sending related shares jumping and clearing shelves of disinfectants even as some questioned the findings.

Based on limited trial on a group of 41 patients with mild symptoms, gargling with diluted povidone-iodine four times a day reduced the number of those testing positive to 9.5 percent after four days, compared with 40 percent for a group who gargled with just water, Gov. Hirofumi Yoshimura said at a press briefing on Tuesday.

Povidone-iodine is an antiseptic more commonly known as betadine. In Japan, it’s sold as gargle medicine by Shionogi & Co, using the name Isojin under license from Mundipharma, as well as by Meiji Holdings Co. Meiji, which did not immediately respond to a request for comment from Bloomberg News, saw its shares surging as much as 7.7 percent in Tokyo following the news. Shionogi rose as much as 3.6 percent.

“It’s worth giving a try,” Yoshimura said, recommending its use to residents with symptoms and those working in high-risk industries such as bars, restaurants and health care. “It’s a drug that everyone can buy at a drug store and it doesn’t do any harm.”

The finding isn’t based on data from a large, randomized, controlled trial — the gold standard for assessing the safety and efficacy of any potential therapy. When asked by a reporter if it was appropriate to be touting the medicine at such an early stage in its research, Osaka Mayor Ichiro Matsui, who was also speaking at the briefing, questioned back if he was supposed to ignore the findings.

“We’ve always been asking people to gargle, in addition to washing their hands, wearing a mask and social distancing,” said Matsui. “Now we’re just saying there were better results when they gargled with this instead of gargling with nothing.”

At a Matsumotokiyoshi Holdings Co. drug store in Chiyoda Ward, Tokyo, the shelves were stripped clean of gargle medicines containing povidone-iodine, including Meiji’s brand, as of 3:30 p.m. Tuesday. Three nearby stores were also empty. Amazon’s Japanese website listed most related products as being sold out.

“We hadn’t heard anything prior to the governor’s press conference,” said Meiji Holdings spokesman Hirosaki Oode. “Our product is effective at disinfecting the mouth and throat, as well as combating bad breath. We have no plans to study its effectiveness against coronavirus at this time.”

Osaka Gov. Hirofumi Yoshimura speaks at a press briefing on the coronavirus pandemic on Tuesday. | KYODO
Osaka Gov. Hirofumi Yoshimura speaks at a press briefing on the coronavirus pandemic on Tuesday. | KYODO

People in Japan commonly gargle as a preventative measure against colds and flus in winter, similar to hand-washing, though its effectiveness is still a matter of some dispute. A 2005 study by Japanese scientists concluded gargling with water helped prevent upper respiratory tract infections, but didn’t find using povidone-iodine any more effective than water, though a much smaller study on just 23 patients in 2003 did.

Along with hand-washing and mask-wearing, the habit was one of the early factors suggested as among possible reasons Japan escaped the initial brunt of the virus relatively unscathed. In recent weeks however, cases have flared up across the nation, with infections in Osaka on some days coming close to surpassing Tokyo despite a much smaller population.

The rush to find something to stem the spread of the pandemic has led to multiple treatments being hailed worldwide as a potential silver bullet for the disease before sufficient data can back those claims up, from hydroxychloroquine touted by U.S. President Donald Trump, to Fujifilm Holdings Corp.’s antiviral drug Avigan.

“I even think that gargling with povidone-iodine could defeat the coronavirus,” Yoshimura said. “But it’s still in the research phase and we can’t say anything definitive.”

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