GlaxoSmithKline (GSK) has suspended patient enrolment in trials of GSK'052, an antibiotic for complicated urinary tract and intra-abdominal infections licensed from Anacor Pharmaceuticals.
Anacor said in a statement that GSK has called a temporary halt to four studies while it investigates a "microbiological finding" in a small subset of patients who have been treated with GSK'502, a systemic antibiotic for the treatment of infections caused by Gram-negative bacteria.
The patients were being treated in a phase IIb trial in complicated urinary tract infections, but GSK has also decided to stop a phase IIb trial in intra-abdominal infections as well as two phase I studies in healthy volunteers.
"We will work with GSK to better understand this microbiological finding, which we anticipate could take several months," said Anacor chief executive David Perry.
GSK'052 is an important new compound, as many commonly used antibiotics do not work against Gram-negative bacteria and resistance to existing therapies continues to be a growing problem.
Those that have activity against Gram-negative infections tend to be poorly-tolerated and, unlike GSK'052, are not available in both oral and intravenous formulations, so patients cannot continue on the same antibiotic therapy they received in the hospital once they are discharged.
The nature of the microbiological finding has not been disclosed, but Anacor said it was unrelated to safety and patients already receiving the antibiotic will be able to continue to receive treatment at the discretion of the clinical investigator.
The primary concern lies in the possibility that the finding could have a bearing on the efficacy of the treatment.
"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," said Anacor in a statement.
"Upon completion of the review, GSK will determine next steps regarding the future development of GSK '052," it added.
GSK licensed rights to GSK'052 (formerly AN3365) in July 2010 for an upfront fee of $15m, development and commercial milestones of up to $244m and double-digit tiered royalties on sales.
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