What you are describing in your 3 year old German Shepherd mix sounds like Pyoderma.
Pyoderma is a bacterial skin infection that is seen as red pimple-like lesions or flat circles, usually found in the groin area, and the armpit area and often on the underside of the neck. The little red spots may look like tiny pimples and they are filled with bacteria and pus.
Let me explain how this happens...
There are normally small numbers of bacteria living on the skin surface, but when they invade the skin like this it is called pyoderma. This can happen if there is a small scratch, flea or mosquito bite, or cut in the skin surface. It is particularly common when the weather is hot and humid, as the bacterial and yeast numbers are very high in those conditions. We also see it any time the dog is getting wet frequently (rain or snow on the dog when outside), but it can happen at any time of year.
Pyoderma causes the dog to be very itchy. Think of yourself if you have a small scratch on your arm – it may become very itchy if it gets infected. Then multiply that by 100 and you can imagine how itchy your poor dog may be!
Here is more information:
If this rash is in more than one small area your dog will probably need to go on oral antibiotics to get it under control.
Oral antibiotics for skin infections are often given for 2-4 weeks in order to resolve the problem. Often, when dogs are really itchy and irritated, I also put them on a course of anti-inflammatory such as prednisone to provide instant relief from the itching.
If, however, you want to try to treat this at home first, you could use a benzoyl peroxide shampoo but make sure to condition afterwards (I recommend an oatmeal conditioner).
You can get the shampoo at your veterinary hospital, or at a big pet store (PetSmart might have it) or on-line. Try shampoo/condition her once and see if there is any improvement.
If there isn't, I suggest you take her to your veterinarian.
I'll give you some links:
example of Shampoo: http://www.allivet.com/DermaPet-Benzoyl-Peroxide-Plus-Shampoo-p/26935.htm
example of Conditioner: http://www.calvetsupply.com/index.asp?PageAction=VIEWPROD&ProdID=373
When I have clients phone me after hours about this, for patients that I have seen, I advise the people that they may be able to give their dogs BENADRYL (diphenhydramine). This should not be given if the dog has glaucoma.
I ADVISE OWNERS TO MAKE SURE IT IS PLAIN DIPHENHYDRAMINE WITH NO OTHER INGREDIENTS.
The dose that one generally gives is 1mg/lb.
It comes as 25 mg tablets, and as she is 80lbs, her dose should you choose to use it would be THREE TABLETS. This can be repeated every 8 hours for 24-36h.
Here is more about Benadryl:
You should see improvement within 30 minutes (less itchy). It can cause drowsiness.
It is likely your girl will need antibiotics to treat this. However, until you can get to the vet, you may be able to provide some relief for her with the shampoo, conditioner and Benadryl.
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.
Good luck with your dog!