Penetration Enhancers for the Development of Intranasal Formulations for Use in Equines

The aim of this review is to assess penetration enhancers, such as cyclodextrins, chitosan and their derivatives, surfactants, bile acids, their salts and derivatives, sodium taurodihidrydrofusidate, and phospholipids used in the development of intranasal formulations with a potential application in horses. In the last few years, the interest in the intranasal administration route in humans has grown because it is bloodless, noninvasive, and painless and represents a direct path toward the central nervous system. However, in equine medicine, the use of this administration route is scarce. Since equines have a nasal cavity with large surface area and blood irrigation, a high bioavailability of intranasal administered drugs is expected. Nowadays, the development of formulations for intranasal administration in equines is a challenge. The present review proposes the assessment of the characteristics and potential effects of the most important penetration enhancers in the development of intranasal formulations for use in equines.