The addition of azithromycin to standard of care does not reduce the risk of hospital admission or death in patients with mild-to-moderate COVID-19, a new clinical trial shows.

“At the time the study was started, we really didn’t know whether this approach would have no effect or whether it would potentially have a very large effect,” said Dr. Timothy Hinks of the University of Oxford in the U.K.

“Now,” he told Reuters Health by email, “combined with data from the other major trials, we are confident this is not a useful treatment for COVID-19.”

Azithromycin, an oral antibiotic, gained interest last year when global agencies sought to repurpose existing medicines as treatments for COVID-19. The drug had previously been used to treat Middle East Respiratory Syndrome (MERS), and in vitro tests suggested it was also effective against a range of other viruses.

The new study enrolled adults who presented to 19 different hospitals in the U.K. with either clinically diagnosed, confirmed, or highly probable COVID-19 and fewer than 14 days with symptoms. Their average age was 46 years and about half were men.

The median duration of symptoms prior to enrollment was six days, Dr. Hinks and colleagues report in The Lancet Respiratory Medicine. They randomly assigned participants to once-daily oral azithromycin 500 mg for 14 days plus standard care (n=147) or standard care alone (n=148).

Over the 28-day assessment period, there was no significant difference between the group of patients assigned to azithromycin versus those given only standard of care in regard to hospital admission or death (10 percent vs. 12 percent, respectively; adjusted odds ratio, 0.91; P=0.80).

Nor was there a difference between the groups in regard to the time to hospitalization (adjusted hazard ratio, 0.95; P=0.89).

A total of two participants (1 percent) in each treatment group died or required level-2 or -3 ventilation. There were no serious adverse events reported in either group.

While authorized COVID-19 vaccines represent the best-known available strategies to prevent infection and/or severe disease, Dr. Hinks pointed to recent work suggesting a protective benefit from taking an asthma inhaler called budesonide.

“However, we need to confirm the promising work on inhaled budesonide in early disease using larger studies,” he said. “This, among other strategies, is likely going to becomse more important as it increasingly looks like we’ve never established ‘herd immunity’ and COVID-19 is here to stay, with new variants arising all the time.”