How fast and complete the spreading is depends on a lot of factors (e.g. distance to the delivery point, rain, animal behavior such as grooming, licking, rubbing, etc.) but also on the inert ingredients in the formulation, which may or may not favor spreading. In any case, compared with the backline the concentration of theactive ingredient will be significantly lower in body parts that are difficult to reach (e.g. udders, perineum, below the tail, inside the ears, etc), where some parasites may survive because the concentration is not high enough to kill them. Irregular spreading may also cause chronic exposure of some parasites to sub-lethal doses, which is known to favor development of resistance.
Todos lospour-ons no sistémicos como este producto tienen el inconveniente de que la cobertura de la superficie del cuerpo del animal con el ingrediente activo puede ser incompleta, sobre todo en partes del cuerpo difíciles de alcanzar (p.ej. las ubres, bajo la cola, las patas, etc.).