How effective is pet external deworming?

The effect of external deworming depends on the product used. Generally choose external products with selamectin, imidacloprid or moxidectin; for fleas and lice consider fipronil. Different ingredients target different parasites, so they can be used alternately.

Many external parasites have a roughly 28-day breeding cycle, so external deworming should be done monthly. If used only two or three times a year, the pet may still get infected.