Zodiac flea treatment comes in a variety of forms, and two different types: one for cats and one for dogs.  Be careful not to treat the dog formula to cats, or vice versa.

You can get a shampoo, spray or powder.  Cats tend to not like getting wet so the shampoo option may not be as good as either a spray or a powder for them.  Follow the instructions carefully for each variety.  While the shampoo should of course be used all over the pet, other treatments only require that the most flea affected areas be treated, for example just behind the head and at the base of the tail.  Once you have applied the treatment, you should watch out for any adverse reactions, which is always a danger when using chemical-based products.  In particular, you should watch out for allergic reactions such as hives or swelling on the face. 

Merely treating your pet, however, will not be sufficient in getting rid of the flea infestation, as the eggs of fleas fall off the pet and onto the ground, where they will go through larval and pupal stages before finally emerging as an adult flea, ready to latch onto your pet.  If you only treat the pet with Zodiac flea treatment, therefore, even though you might get rid of all the fleas on their body, more will soon attack them again if you have not also treated the environment. 

The standard way of keeping the area clean of developing fleas is to keep vacuuming the carpets and washing the bedding as well as clearing the garden of the flea material.  There are a variety of natural and non-chemical means for doing this, but Zodiac flea treatment also includes the option of a House Spray, which will provide a more robust method of getting rid of developing fleas.

It is important to rid your pet of fleas as soon as possible as, beyond merely being an irritant, they can also carry diseases which can make your pet seriously ill.  However, you should also consider whether the treatment you are using is causing more harm than the fleas themselves, and sometimes with chemical products this can be the case.  Different products will work better with different animals, and Zodiac flea treatment may well be your best option, however for a general idea of how effective a product is, and how harmful it might be, you can check out consumer reviews on the internet, ask a professional pest controller or contact your vet.