A Case Study of Overestimating Absorption and Circulating Metabolites Due to the Preferential Absorption of Radiolabeled Drug in a Mass Balance Study.

Assuming the radiotracer was proportional to total drug throughout a radiolabeled study was not valid in a 14C study in beagle dogs. This presumably resulted from unequal absorption of the radiotracer and nonradiolabeled test articles from the oral dose due to inequivalent solid forms. We were able to provide a more accurate description of the AME of GDC-0276 in dogs by characterizing the differential absorption of the radiotracer.