Conceptual and commercially available intravaginal veterinary drug delivery systems.

In the veterinary area the utilization of the vagina as a route for drug delivery has focused on the systemic delivery of hormonal steroids to control synchrony, ovulation and fertility in a variety of livestock. There are several reasons for administering drugs to modify the menstrual cycle in humans and the estrous cycle in animals and this paper provides a comparison of the objectives of drug intervention to control reproduction in humans and livestock. In addition, the types of hormones and their concentrations found during the menstrual cycle in humans and during the estrous cycle in animals are compared. The paper also reviews the intravaginal drug delivery systems developed for the control of the estrous cycle in livestock and both conceptual and commercially available intravaginal drug delivery systems that have been described in the literature are described. The history of some of the delivery systems is included and the future directions of this area of research are discussed.