This invention provides methods of controlling pain in a canine comprising transdermally administering a composition comprising fentanyl, a penetration enhancer, and a volatile liquid, wherein the composition is a solution. The invention also provides a single unit dose of the composition.USO DE UNA COMPOSICION QUE COMPRENDE FENTANILO, UN INTENSIFICADOR DE LA PENETRACION Y UN LIQUIDO VOLATIRL PARA PREPARAR UN MEDICAMENTI UTIL EN EL TRATAMIENTO DEL DOLOR.