The FDA has approved Merck & Co's bezlotoxumab to reduce the recurrence of Clostridium difficile infection, marking the first approval for a new approach to the treatment of bacterial infections. Unlike antibiotics, which kill pathogenic bacteria, bezlotoxumab is an antibody that mops up toxins that are released by C. difficile.

Although antibiotics can control C. difficile, the infection recurs within weeks in around 25% of patients. In two phase III trials that tested bezlotoxumab in conjunction with standard of care antibiotics, Merck showed that their adjunct antibody reduced recurrence to 16–17% of patients. The most common adverse reactions included nausea, pyrexia and headache.

Analysts expect the market for bezlotoxumab to be modest, at US$212 million per year in worldwide sales by 2020. However, the approval could boost interest in the growing pipeline of antibodies for the treatment of bacterial infections (Nat. Rev. Drug Discov. 14, 737–738; 2015).

In some cases these antibodies, like bezlotoxumab, act on bacterial toxins. AstraZeneca's phase II candidate MEDI4893 targets the Staphylococcus aureus alpha toxin, for example, and Bellus Health's phase II shigamab targets the Escherichia coli shiga toxin type 2. Other antibodies target the bacteria more directly. AstraZeneca's phase II candidate MEDI3902, for example, targets the exopolysaccharide PsI and the secretion protein PcrV on the body of Pseudomonas aeruginosa bacteria.

One benefit of these targeted antibodies is that they might be less likely to induce broad resistance among bacteria or disturb the healthy microbiome.