Fidaxomicin (Dificid, Dificlir) is the first in a new class of narrow spectrum macrocyclic antibiotic drugs. The originator product Merck’s Dificid only received approval from FDA in May 2011 for the treatment of clostridium difficile-associated diarrhoea.

Draft Guidance on Fidaxomicin
Date: August 2016
http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM517624.pdf 

There are as yet no generics of fidaxomicin approved by FDA. However, generics makers looking to gain approval for their fidaxomicin generics have, according to the new draft guidance, two options for demonstrating bioequivalence.

The first option, for fidaxomicin generics with equivalent inactive ingredients to their reference products, allows bioequivalence to be established by conducting both an in vitro comparative dissolution study and an in vivo bioequivalence study with pharmacokinetic endpoints.

The in vitro study should consist of comparative dissolution data for 12 tablets each of the generic and reference products. For the in vivo study, single-dose (200 mg), two-way crossover studies should be carried out in healthy men and non-pregnant women under both fasting and fed conditions.

The second option, for generics that do not have the same quality and quantity of inactive ingredients as their reference drug, advises generics makers to conduct an in vivo study with clinical endpoints in patients with clostridium difficile-associated diarrhoea.

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FDA releases 47 new and revised bioequivalence guidelines for generics

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