GSK is in the process of obtaining additional information in order to better understand the data, but will not resume the trials until it has concluded its investigation. Upon completion of the review, GSK will determine next steps regarding the future development of GSK '052.

In addition to the Phase 2b study in cUTI, GSK '052 is currently being evaluated in a Phase 2b study in complicated intra-abdominal infections (cIAI) and two Phase 1 studies in healthy volunteers. While the microbiological finding seen in the cUTI study is not related to the safety of GSK '052, the potential to negatively impact efficacy led GSK to voluntarily suspend enrollment in all four studies. Subjects who are currently enrolled in the ongoing studies may continue at the discretion of the investigator.

"We will work with GSK to better understand this microbiological finding, which we anticipate could take several months," said David Perry, CEO of Anacor Pharmaceuticals. "We respect GSK's decision to pause enrollment in the current studies as we fully investigate the microbiology finding in the Phase 2b cUTI patients."

Anacor licensed GSK '052 to GSK in July 2010 under the companies' ongoing research and development collaboration.