Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that your fellow is miserably itchy even with Vetalog.
Vetalog is a pretty potent steroid, so if he remains itchy even with that then antihistamines may not work either, but you can try them.
There is no contraindication against using steroids and antihistamines at the same time.
You can use a combination of antihistamines and high doses of omega-3 fatty acids to help with the symptoms of allergies in dogs. In combination fatty acids and antihistamines work synergistically, much better than either one alone.
You can try:
1)Benadryl (diphenhydramine only don't use the combination products with acetaminophen or decongestants as they can be toxic for dogs) at a dose of 1mg to 2mg per pound of body weight or one 25mg capsule per 15 to 25 pounds of body weight orally every 8 hours.
OR 2)Claritin (loratidine) at a dose of 5mg per 25 pounds of body weight once or twice daily.
OR 3)Hydroxyzine at a dose of 1mg per pound of body weight orally every 8 hours.
OR 4) Chlorpheniramine at a dose of 4mg to 8mg per dog once or twice daily.
OR 5) Zyrtec (Cetirizine hydrochloride) at a dose of 1/2 mg per pound of body weight orally every 24 hours. That would be one 10mg tablet per 20 pounds of body weight. Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because dogs cannot tolerate decongestants.
Some dogs do better on one antihistamine rather than another. Give the one you pick a 5 day trial and if it isn't working try another. Be aware antihistamines can cause sleepiness or hyperactivity in some dogs. These side effects do wear off with repeated use.
Omega-3 fatty acids are fish oil products. 3V by DVM or Derm Caps ES are good brand name products. Use the high end of the dosing schedule for your pup's weight, meaning if he is between doses work up to the higher dose. I recommend a dose based upon the EPA portion (eicosapentanoic acid) of the supplement as if we do that the rest of the supplement will be properly balanced. Give him 20mg of EPA per pound of body weight per day. For example an 8 pound dog could take 160mg of EPA per day.
Cool water baths with an oatmeal shampoo or chlorhexiderm shampoo (which is antibacterial and antifungal) and a conditioner with an antihistamine may help. The water rinses off allergens and the cool temperature soothes itchy skin. Do not bathe your fellow for 2 to 3 days before or after applying flea control products or the bath will interfere with the product's efficacy.
Food allergy is very possible with him as well if he seems to be itchy all year round and steroids don't seem to help. Dogs with food allergies may not improve even when given potent steroids. Dogs can develop allergies to any protein or carbohydrate so even if he is only fed one thing that can be what he is allergic to. Dogs with food allergies tend to lick and scratch their paws, face and ears the most, but any of the "allergy reactive areas" can be affected.
Make sure that the food that you put him on is a true hypoallergenic diet. The trouble with "limited ingredient" or "low allergy" pet store brands is that the same machinery is used on multiple lots of food without sterilization cleaning in between. So for example even if a food says it has salmon and rice if the previous batch had beef and corn then you will get traces of those ingredients in your bag of food. Not a big deal if your dog isn't allergic but a waste of money thinking that the food was hypoallergenic and not good for your dog if those happen to be allergens for your dog. The veterinary brand true hypoallergenic foods are more expensive because it isn't cheap to thoroughly remove all traces of a previous food mixture from the machines used to process food.
Generally what I recommend is trying to clear the skin with a prescription hypoallergenic food and then adding one food item (chicken, beef, corn, wheat, etc) every month to see what they react to. Then we can find a regular food to try that doesn't contain the ingredients that they react to. As far as permanent diets I do tend to stick with Purina Pro Plan brands or Nature's Recipe as I find those rarely if ever have cross contamination. Purina Pro Plan Turkey and Barley or Nature's Recipe Vegetarian or Venison are pretty good products. I know that this isn't easy from personal experience (my dog is allergic to wheat) and it is time consuming, but worth it.
If you choose to try testing/treating him for a food allergy I recommend that you try a true hypoallergenic diet like Hills z/d or Purina Veterinary Diets HA. No treats, flavored medication or bones while on the diet and it must be used for a least 12 to 16 weeks to see the full effects. You should see some improvement in 6 to 8 weeks.
Dogs with sarcoptic mange or cheyletiella mites also may be intensely itchy and may not improve with steroids, so if he isn't coming along testing for those mites should be done.
Please let me know if you have any further questions.