The pill, Brexafemme, made just $1.6 million in revenues in the third quarter of last year, according to the most recent financial results from Scynexis, which specialises in anti-fungal treatments.

But GSK's Chief Commercial Officer Luke Miels told journalists he was confident that, as a big pharma company with experience building awareness among doctors and patients, GSK could change the trajectory of the product over time.

Up to 75% of women have at least one episode of vulvovaginal candidiasis, commonly known as a vaginal yeast infection, in their lifetimes, according to the U.S. Centres for Disease Control and Prevention. Brexafemme is the only oral pill treatment approved by the U.S. Food and Drug Administration regulator, GSK said in a statement.

Miels said GSK was attracted to the deal in part because Scynexis had difficulty - which he said was common for biotech firms - garnering adequate investment to make medical professionals and potential customers in the U.S. aware of the oral treatment.

"We think that's just a function of scale," he said, adding GSK had a strong record over the past five years of launching primary care treatments like its blockbuster Shingrix vaccine.

The agreement announced on Wednesday also gave GSK rights to develop the medication for the potential treatment of invasive candidiasis, a life-threatening fungal infection, which is currently in late-stage clinical trials. It expects to launch the product for that indication in 2026, Miels said.

GSK has two other antibiotics in development, including gepotidacin for uncomplicated urinary tract infections, which is in late-stage trials.

It is one of a small number of big pharma companies investing in research for next-generation antibiotics, where there has not been a major breakthrough in decades, fuelling concerns about the rise of drug-resistant bacteria and other microbes due to the misuse and overuse of antibiotics.

(Reporting by Maggie Fick; Editing by Mark Potter)

By Maggie Fick