Los Angeles: The antibiotic commonly prescribed for COVID-19, azithromycin, is no more effective than a placebo at preventing viral illness in outpatients, and may actually increase their chances of hospitalization, according to a study.

The research, published in the Journal of the American Medical Association, included 263 participants who all tested positive for SARS-CoV-2, the virus that causes COVID-19, within seven days before entering the study.

None of the participants were hospitalized at the time of registration.

Researchers at the University of California at San Francisco (UCSF) and Stanford University in the United States randomly selected 171 participants to receive a single oral dose of 1.2 grams of azithromycin and 92 received a identical placebo.

On day 14 of the study, 50% of participants remained asymptomatic in both groups.

By day 21, five of the participants who received azithromycin had been hospitalized with severe symptoms of COVID-19 and none of the participants in the placebo group had been hospitalized.

“Among ambulatory patients infected with SARS-CoV-2, treatment with a single dose of oral azithromycin compared to placebo did not result in a greater likelihood of being symptom-free by day 14,” wrote the authors in the study.

The researchers concluded that treatment with a single dose of azithromycin compared to placebo did not result in a greater likelihood of being asymptomatic.

“These results do not support the routine use of azithromycin for ambulatory SARS-CoV-2 infection,” said lead author of the study, Catherine E. Oldenburg, assistant professor at UCSF .

“The hypothesis is that it has anti-inflammatory properties that can help prevent progression if treated early in the disease. We haven’t found this to be the case,” Oldenburg said.

Azithromycin, a broad-spectrum antibiotic, is widely prescribed as a treatment for COVID-19 around the world.

Most of the trials done with azithromycin so far have focused on hospital patients with fairly severe illness, the researchers said.

“Our article is one of the first placebo-controlled studies to show no role for azithromycin in ambulatory patients,” added Oldenburg.