Xenobiotic transport proteins play an important role in determining drug disposition and pharmacokinetics. Our understanding of the role of these important proteins in humans and pre-clinical animal species has increased substantially over the past few decades, and has had an important impact on human medicine; however, veterinary medicine has not benefitted from the same quantity of research into drug transporters in species of veterinary interest. Differences in transporter expression cause difficulties in extrapolation of drug pharmacokinetic parameters between species, and lack of knowledge of species-specific transporter distribution and function can lead to drug–drug interactions and adverse effects. Horses are one species in which little is known about drug transport and transporter protein expression. The purpose of this mini-review is to stimulate interest in equine drug transport proteins and comparative transporter physiology.

An 8 month old boxer dog was referred for management of acute spontaneous pneumothorax. CT showed multiple variably sized bullae in the right middle lung lobe, and partial or complete atelectasis of all remaining lung lobes. This was assumed to be a case of congenital lobar emphysema (CLE). The dog was anaesthetised for surgery but died from cardiopulmonary arrest during presurgical thoracocentesis. Postmortem examination confirmed that ruptured bullae in the right middle lung lobe were responsible for the dog's pneumothorax and death. In addition, a malformation of the right subclavian artery was present. Histologically, the right middle lung lobe and primary bronchus were malformed, with microscopic changes resembling those of human congenital pulmonary airway malformation (CPAM), rather than CLE. CPAM has not been reported in the veterinary literature and should be considered in the differential diagnosis for spontaneous pneumothorax in dogs.