Cetirizine antihistamine dosage for dog?

[ViviPru]

My basset has a swollen face, I think she might have had an allergic reaction to a bite or sting. I have read that i can give her cetirizine, but the dosage advice is not clear, advice seems to be take her to the vet and ask but she's booked in tomorrow for something else anyway and If I can avoid going twice that would be preferable... She is 19.5kg, any idea what does of cetirizine I could give her?

Thanks!

Dose should only be advised with your dogs medical history. Cetrizine is not one I routinely use.

Ok thank you. It doesn't appear to be getting any worse and she's not showing any signs of discomfort so I think I will keep an eye on it and wait until we see the vet tomorrow.