Harvey had a steriod injection last night which seems to have really helped him as he isn't scratching nowhere near as much as he was although he has had a few itchy moments. I wondered for how long should the steriod injection offer relief? The vet has asked me to bring him back when he flares up again but never told me how long the injection should work for.

When this has happen with mine and the vet has given and injection (hot spots or just scratching with no apparent cause) I have found that the problem has subsided and just didn't reoccur. The dog that used to get hot spots occasionally had another injection if a hot spot happened again.
Not sure if that is helpful I think it is a wait and see thingy. Others may have different opinions.

I will be over the moon if it is a long lasting remedy for Harvey. He also has a bacterial skin infection and has a 10 day course of anti biotics to treat that so hopefully he will be better when the infection goes.

Poor harvey hope he feels better soon.

Steroids are usually short term for skin problems and ear infections, they have side effects as everything does, I know dogs on steriods for life, but small dose's.

My pup has allergies and sufferers badly from itchy skin. He has a steroid injection followed by 15 days of oral steroids and antibiotics when he starts itching.
The injection usually last 48 hrs and then he has to start the tablets. The steroids work fantastically but aren't a long term solution especially as my boy is so young. Our next course of action is to start immunotherapy treatment.

I presume the vet has ruled out all the common causes of itching such as mites.
If he has responded quickly to steroids I would have thought that there is a good chance that he has some form of allergy.
Has the vet offered any allergy tests? 

The bacterial infection is often just a result of the scratching but my vet now gives a 21 day course at first just in case.

I hope Harvey is feeling a little more comfortable now.

Hello Hugos there. Sorry to learn about your pup suffering allergies - its awful to watch them so itchy isn't it. Harvey has had skin scrapes and there were no mites or mange thankfully. We are certain that he has an allergy of some sort and the vet has asked me to bring him back when and if he has the next flare up. He did mention going down the allergy testing route but said that the tests were very expensive (not that this will hamper his treatment - I will pay whatever necessary to get to the bottom of this) and that we should go one step at a time. The fact that he is on a good grain free diet gives us reason to believe that his allergies are caused by contact to something.

> The fact that he is on a good grain free diet gives us reason to believe that his allergies are caused by contact to something.

A high quality meat based, grain free diet will still cause a probelm for dogs with sensetivities to meat proteins.
My last dog had a sensetivity to chicken, to such an extent it would cause his ears to become inflamed, swollen, waxy & then infected, the lesser side effect he had from eating chickin was very itchy skin, he would scrat untill he made himself bald :(
I was confinced there was a trigger to his itching & bad ear so I started to keep a log of every ingredient of everything he ate, it then became apparent that chicken was the problem - no expensive tests at the vets needed.