The U.S. Food and Drug Administration approved Merck's (NYSE:MRK) Dificid drug for children aged 6 months and older who have diarrhea caused by a specific bacterial infection called Clostridioides difficile (C. diff).

A tablet form of the drug was already approved for adults with diarrhea caused by the bacteria. In addition to expanding the approval for the tablet form to children, the FDA also approved an oral suspension of the drug that will be easier for children to take than the tablet.

Doctor using a stethoscope on a young boy.

Image source: Getty Images.

Dificid isn't absorbed by the body, making it effective at treating infections of the gut that cause diarrhea, but ineffective at treating bacterial infections in other parts of the body. C. diff causes almost 500,000 infections annually in the U.S., with about 29,000 of those patients dying within 30 days of initial diagnosis.

The drug seems to work as well as vancomycin, which is available as a generic, but appears to have a lower recurrence rate. In a clinical trial run by Merck's collaborator Astellas Pharma, Dificid eradicated the bacteria as well as vancomycin when measured two days after the 10-day treatment. Looking further out, at 30 days, 68.4% of the children taking Dificid were cured of their infection that didn't return, compared to just 50% of children taking vancomycin.

Merck and Astellas ended up owning rights to the same drug through a series of acquisitions and licensing deals. Merck gained access to Dificid through its 2015 acquisition of Cubist Pharmaceuticals, which had acquired the drug's original developer, Optimer Pharmaceuticals. Before that, Astellas had licensed rights from Optimer to sell the drug in Japan and Europe, where it's marketed as Dificlir.