This third generation cephalosporin may cause red stools when administered with products that contain iron.
A case report by Graves et al. reports a 7 month old female that was evaluated for 'bloody stools' and found to have red stools from cefdinir along with an oral iron supplement. The incidence of red stools with cefdinir is unknown though one small study reported red discoloration in stool to occur in 4 out of 39 children. (Graves R et al. Cefdinir-Associated "Bloody Stools" in an Infant. J Am Board Fam Med 2008; 21:246-248.)