How much Piriton??

Hi,
Eva had recently (last 2 weeks or so) been constantly scratching at her 'eyebrow' bits, shes worse on a night iv noticed. Saw a post on [a social network] yesterday about dogs getting hayfever and one of the symptoms was scratching the eyes, so im wondering if its that was going to try her on piriton before taking action and going to the vets.
Does anyone else use it?
wondering how many tablets to give her a day, shes a medium sized Staffy x @ 21kg.
Does it have to be piriton or can it be a 'own brand' make?

Thanks

Piriton is chlorphenamine maleate the dose is:

4 – 8 mg large dog x 2 a day, 2 – 4 mg x 2 a day small ones

Pititeze is ceterizine it is not as well researched
as chlorphenamine maleate.

Cetirizine has been trialed on dogs for allergic skin disease at 1mg/kg with minimal side effects

There are many anti histamines with many different ingredients thus if you choose a generic one choose that which is chlorphenamine maleate