I am sorry to hear about Blue.
My name is Rebecca. I am a veterinarian, and will do my best to help.
Do you mean giving him an injection into a particular painful joint?
Or an IV injection in a vein in the front leg?
We sometimes do give cortisone injections into joints, to give some relief to a painful joint, but the effects are temporary.
Giving an injection just into a muscle or vein or under the skin of the front leg would be no different than giving an injection anywhere on her body; it would work in her blood stream and have systemic effects all over her body.
If she is taking anti inflammatory pills, those should be stopped before giving a cortisone injection. They can cause vomting and diarrhea if you give both at the same time.
I am not seeing responses from you; I hope you see what I am writing.
I will try to connect with you another way if I do not hear from you soon.
Sometimes this live chat has problems and we do not see what the other is saying.