Andrea is correct it is 1mg/lb. If you Jack Russell weighs 12 pounds give him 1/2 a 25 mg table 2 - 3 times daily. You can also add in tagament (it will help block the histamine receptors in his stomach - sounds strange but it does work). An oatmeal bath may help too. I personally would only use steroids if it is a severe reaction and your buddy is extremely uncomfortable. If you have any concerns/questions it is best to contact your vet.