Drugmakers seeking approval of fidaxomicin generics to treat Clostridium difficile-associated diarrhea have two options for demonstrating bioequivalence, the FDA said.

The first option is for fidaxomicin generics with equivalent inactive ingredients to their reference products, according to FDA draft guidance published last week.

In this case, the FDA recommends an in vitro comparative dissolution study and in vivo study with pharmacokinetic endpoints.

The in vitro study should consist of comparative dissolution data for 12 tablets of the generics and reference products, while the in vivo study should be conducted on among healthy men and nonpregnant women with a single dose of 200 mg.

The alternative choice covers generics that do not have the same quality and quantity of inactive ingredients as their reference drug. In these instances, the FDA advises drugmakers to conduct an in vivo study with clinical endpoints in patients with Clostridium difficile-associated diarrhea.