Just a couple of weird not-typical ideas
First, when antihistamine touches it **not at all** and particularly when someone describes the dog as waking from a sound sleep TO scratch, one of the things I always suspect is sarcops (sarcoptic mange mites).
Don't jump to conclusions on me here -- we all have the typical stereotype "but sarcops are only in dirty places" ... NOT true. Most of the time, sarcoptic mange mites like to stay with their chosen host. i.e., the bum on the corner and his dog -- the bum, himself, may have contacted scabies but generally they will stay on HIM, not the dog, or if his dog has sarcops they won't bite the man. Because each variety of sarcops likes to get their blood feast from their normal host (like scabies mites want human blood but also they want to reproduce in human skin).
There is a variety of sarcops out there for every single different species that is warm-blooded I think. HOWEVER -- in these days where natural resources are diminishing and urban crawl is taking up more and more of the space where wild critters used to be, this is changing.
At this point, it's not uncommon for any wild animal to have sarcops -- but that coon sitting up in your tree that scratches and a couple of the mites fall off, only to be picked up by the next red-blooded animal that walks that way. The mites may literally only be interested in a blood feast (but when they bite that's when the vicous itchy venom is injected that makes the horrific itch), and they may or may not attempt to lay eggs in that creature's skin -- but they are finding the mites are willing to generalize to survive -- and more and more wildlife sarcops are becoming a problem to dogs and domestic species.
My point -- dogs that have access to the outdoors -- particularly one like Bugs who lives near other wild critters -- he could be harassed by wildlife sarcops -- you might not see the tell-tale bumps where eggs have been laid -- but you will see the results of them getting bitten in the violent itch.
It's just a possibility. The only "easy" solution is either Lyme Dip (which smells like rotten eggs but is a relatively safe topical pesticide that even humans can use on their skin) or ivermectin/milbemycin in sufficient dose to kill sarcops (i.e., not a heartworm preventive dose -- the dose to kill sarcops is relatively high for both of those). If you think this is a possible -- discuss it with your vet plainly -- including making the vet aware of how vicious this itch is and all your efforts to stop it.
Now, that's not to say that the next time he goes for a walk he won't get walloped again.
Sorry -- this is long -- but it IS a possible. It may not be likely -- but I've seen times when it really has aggravated a typical allergy dog's problem. Billy even tangled with wildlife sarcops at one point. Just thinking about the danged sarcops made ME so itchy that after I wiped him down with Lyme Dip *I* did myself, too. ugh.
Question -- are any of the residential humans bothered by even a brief little nasty red rash? Typically somewhere near where you may sit and cuddle with the dog? Jackie - in your case, sarcops won't always go from dog to dog -- but they do like the ones even moderately immune-compromised like an allergy dog. That's another red flag that you might be dealing with sarcops.
Possible helps
A. Dogs can take most ANY antihistamine humans can but their dose is always different. I don't have my Pill Book Guide here at work, but one other anthistamine that tends to be really good on dogs is Tavist (clemastine, if I recollect correcctly). But switching to a different antihistamine can be helpful -- vets often prescribe hydroxyzine but it's typically less strong than either Benedryl or Tavist.
B. Homeopathics -- this is where I really got into homoepathics for dogs -- the down side is they don't last long in the body -- you have to give them more frequently. And if you are browsing the selection of homeopathics at Whole Foods or similar, you really want a BLEND, not one of the little blue tube "singles" of Boiron's.
Apis is the best for dog allergies (because of how it comes out on the skin, rather than sinus/eyes with humans) -- so either choose a blend that has apis in it, or choose a blend like Hyland's "Oak and Ivey" that is made for skin allergic reactions.
Hylands also has one called "Hives" that is particularly good. Newtons (that's a brand) is often used on dogs because it's a liquid -- you just squirt it under their lip so it drips over their gums/into the mouth.
The little pills that the rest of these are -- don't put them in food. Fold a 3X5 card and crush and pour the powder in their mouth or let them lick it up. Mine will actually CHEW them up (which is best).
Homeopathics have to absorb in the mouth. Don't combine them with food or put in their water.
With a homeopathic a "loading dose" is often helpful -- Give it the first time, and then give it again in half an hour. Then every 4 hours.
The upside? No sleepyness, and no dry mouth. Virtually side-effect free.
Billy did particularly well on -Heel's Allergy blend (Karen, same company that makes Traumeel -- and DO give Bugsy a Traumeel after you give him the Allergy blend if you use that -- Traumeel will reduce the inflammation and help balance the immune system's on/off mechanism).
Tink, on the other paw, does really well on Hylands "Oak & Ivey". I used that on her even for the nasty itch of demodex when she was a puppy.
Sorry this is so long but these are both not-often-considered things and you guys are in a difficult place. Billy was THE WORST allergy dog I've ever had, and generally I could bring the itching under control better with homeopathy than I could with antihistamine.
**note please**
Homeopathy is often dismissed by people as being so "weak" that it's no good. It's actually darned strong stuff and can do things you don't even see. IF YOU USE the Blue Boiron tubes -- use them on a one off situation but use NO LONGER than 3 days unless you go get a homeopathic vet to help you. You can make bigger changes with a single remedy than you realize you are making. This is why I'm encouraging you folks new to homeopathy to try the blends. Generally they are extremely safe and can be used indefinitely with safety.
I hope this helps SOMEONE.