The chewing all 4 paws is the give away!!!!
That is highly consistent with a underlying primary environmental or food allergy.
Allergies will 80% of the time be an environmental allergy, with only 20% or less representing food allergies. Some pets, suffer from both environmental and food allergies:
If you want to actual diagnose what in the environment may be causing the allergy, you can do an allergy test. Now, you don’t have to shave half the body and do the old grid test on the skin. There is now a blood test that looks for allergies to weeds, trees, grasses!, molds, even house dust mites.
It is important to also recognize, once the skin is inflamed or has an odor, there is likely a secondary yeast or bacterial skin infection present. It is critical for any secondary infection to be treated aggressively, as the infection itself will contribute to the pruritus (itching or increased licking).
Now, I did say that up to 20% of pets can actually have food allergies. So, to rule-out food allergies you need to do a diet trial.
Summary: The primary protein in most dog foods is lamb, chicken, or beef. The primary carbohydrate is rice or corn. So, you need to change both. The most popular alternative diets are Venison and Potato, Duck and Potato, or Fish and Potato. It is available in prescription formulas (i.e. Science Diet D/D) or you can find some similar foods at the big pet stores like PetSmart or PetCo. I always recommend picking a “limited-ingredient diet” from your vet to ensure you are doing the trial properly. Just make sure that when they say Venison is the "main ingredient" they don't sneak in other stuff like lamb meal or fish meal. A non-prescription option would include Dick Van Patten's brand called Natural Balance. Keep in mind, holistic or all-natural foods are not necessarily any better when trying to remove a food allergy. Chicken is chicken, and rice is rice. When you perform a diet trial, you must stick with the food for 2-3 months to see if there is any benefit. NO OTHER treats or human food can be given during this time period. Remember, a grain-free diet is not necessarily any better. Over 75% of the time, it is the protein in the diet that is the problem. Lastly, even a limited ingredient diet, as explained above, is not good enough. Sometimes, you need to use a food that is processed in such a way, that the body cannot react to it. A popular choice is Science Diet Z/D low allergen or Ultra allergen. They utilize hydrolyzed protein. The body cannot react to the protein in the food.
I would NOT recommend worrying about food at this point. Food issues I usually encourage tackling later when the vet is convinced that the enviornment is not an issue.
TREATMENT OPTIONS (A small representative list - some suggestions you may have already tried)
1. Steroids. Veterinarians will either give an injection that can last from hours to weeks, or send home oral steroids like prednisone or dexamethasone. Steroids can be safe if not used long-term (several months) and if used as directed by your veterinarian. Frequently, the oral steroids will be weaned down to the lowest dose necessary to keep the allergy suppressed.
2. Antihistamines. A prescription of hydroxyzine is common. Sometimes, over-the-counter Benadryl will help. However, for many allergies, antihistamines alone frequently are not good enough to control allergies. But, if your pet is already on steroids, they can help to reduce the necessary dose to keep the comfortable.
Benadryl can be given at a dose of 1mg per pound of body weight. Keep in mind, Benadryl tablets and liquids come in different sizes. So, an approximately 25 pound dog can get a full 25mg tablet or a half of a 50mg tablet. I usually avoid the liquid Benadryl in larger dogs (you would have to give too much of it). You can give Benadryl every 8-12 hours.
Another favorite for dermatologists is Zyrtec (cetirizine) over the counter. Available in 5mg or 10mg tablets. A small dog 10-20 pounds can get a 5mg tablet once a day in the morning, but can be given every 12 hours. Any dog over 30 pounds, I typically recommend the 10mg tablet every 24 hours (or twice a day).
3. Essential fatty acid supplements. Definitely, if you plan to give an antihistamine long-term, combine it with an EFA.
I prefer the veterinary products, which are already dosed for pets. Your vet should carry a product on their shelf, or over-the-internet you can look for Aller G3, 3V caps, EFA-z, or Derm caps.
4. Atopica. A immunosuppressive medication, that help regulate the way your pet’s body reacts to allergens. Neat stuff. It is important to note that it can take several weeks before benefit is observed, and tends to be a bit more expensive than typical allergy treatments.
5. Your vet should also carry some special sprays and shampoos designed for whatever skin condition your pet may have. One of my favorite product lines is called Douxo. They carry various shampoos designed to calm the skin, treat bacteria infections, and help with seborrhea (dry, scaly or scabby skin)
6. Oral antibiotics and/or anti-yeast medication, if indicated. Generally, your vet will recommend a simple skin cytology test to see what is on the surface of the skin. This should be inexpensive, and can be perform in the hospital. This is a key test especially when the skin is itchy, as secondary infections will actually exacerbate the degree of pruritis (itching) of your pet.
7. The newest therapy on the market for allergies is Apoquel:
The above link is a must read if your pet itches, scratches, or chews a lot. Backordering has been a problem with this drug and not all vets carrying it. But, always ask your vet about Apoquel. Has worked amazingly well for every single patient I have been able to get on to it, with far fewer side effects than any drug I have used in the past including steroids.
You can give the antihistamine a try, but almost 100% certain that it will not be sufficient.
Also, you must protect the skin, so invest in a cone head immediately. Any extra licking or chewing is really going to exacerbate the problem.
Hope that information helps