US regulators have agreed to review an experimental antitoxin being developed by Merck & Co to prevent recurrence of the superbug Clostridium difficile.

Bezlotoxumab is designed to neutralise C. difficile toxin B, which can damage the gut wall and cause inflammation, leading to diarrhoea.

The firm is hoping that the drug, given in conjunction with standard of care antibiotics used to fight C. difficile, could offer the first therapy that prevents infection recurrence, which remains a key challenge for healthcare workers. 

According to the US Centers for Disease Control and Prevention, C. difficile is estimated to have caused almost half a million infections in the US alone in 2011, with 29,000 deaths, often within 30 days of initial diagnosis. 

Around one-in-four patients experience a recurrence after the initial episode, and more than 40 percent of these have further recurrence, highlighting the need for new options able to break the infection cycle.

The drug’s application contains data from two pivotal Phase III clinical studies, MODIFY I and MODIFY II, in which the rate of infection recurrence through week 12 was significantly lower in patients given bezlotoxumab (17.4% and 15.7%) or bezlotoxumab and actoxumab (15.9% and 14.9%) than those taking a placebo (27.6%) and (25.7%), respectively.

Om the safety side, the firm said adverse reaction rates were comparable across the bezlotoxumab and placebo arms.

The US Food and Drug Administration is undertaking a speedy review of the drug, with an action date of July 23.