Does advantix retain its efficacy after the dog has been swimming or has had a bath?

Can a reduction in efficacy be observed in dogs treated with advantix which swim frequently?

To evaluate this, studies were carried out which provided for complete immersion of the dog in water for 60 seconds at weekly intervals.
advantix is distributed over the body surface and remains in the lipid stratum which has hydrophobic properties; like all products of this type it is subject to the impact that the duration of baths has on the animal's skin.
Lengthy and frequent baths involve increased cutaneous exchange with greater dilution of the lipid stratum and a consequent reduction in the concentration of product present in this stratum.
The product remains efficacious even if the animal takes a bath. However, in the case of prolonged and frequent exposure to water, it may be necessary to repeat the treatment more than once a month, up to a maximum of once a week.

Does a bath with shampoo (products to counter seborrhoea) reduce the efficacy of advantix? What can one do about it?

The vehicle of advantix, which binds to and transports imidacloprid and permethrin, is organic and of an oily appearance and it means that it can be distributed over the body surface of the dog in the lipid film which covers the skin and coat. This dispersion takes some hours to spread to the whole body and some days to reach the deep strata of cutaneous epithelial tissue and the sebaceous glands.
The use of a normal shampoo before application of the product or a week after this application has not been shown to reduce the efficacy of advantix significantly.
It is probable, on the contrary, that sebolytic products may, because of their ability to remove sebum (= lipid film), significantly reduce the efficacy of the product.
In that case, advantix can be applied again up to a maximum of once a week.