Crystal structure of equine serum albumin in complex with cetirizine reveals a novel drug binding site

•Mammalian SA binds and transports antihistamine drug cetirizine.•ESA crystal structure reveals two cetirizine binding sites, both unexpected.•CBS1 represents a novel drug-binding site.•Cetirizine binding sites are structurally conserved between HSA and ESA.•This study informs on drug transport and delivery in mammals.