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Dr. Kara
Dr. Kara, Veterinarian
Category: Cat
Satisfied Customers: 17944
Experience:  Over 20 years of experience as a veterinarian.
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my cat is 20 years old,takes tablets for thyroid problem.Every

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my cat is 20 years old,takes tablets for thyroid problem.Every so often he develops skin irritation,usually coinciding with the central heating being on more often.He scratches so much that he pulls out fur,and the vet gives him a steroid injection which generally calms things down.However,it hasn't worked this time,and after having two injections within 4 weeks he is still scratching.would it be safe to give him an antihistamine? He has also bee on hypoallergenic food for the past few years.
Hello, my name isXXXXX and I have over 20 years of experience as a veterinarian. I'm sorry to hear that Giggsy is so itchy and uncomfortable.

The most common reason for all over itchiness is flea allergy dermatitis. Flea allergy dermatitis is horrible. In allergic cats it only takes one bite a month for them to itch like crazy. If you don't see any fleas you might not have a huge population and if he is very allergic he may be removing any the evidence with his excess grooming. If you have other pets who aren't itchy they may not be allergic. Ideally you need to apply topical flea control every 3 weeks in an allergic cat as their effectiveness wanes after 3 weeks. Many over the counter products have a problem with fleas being resistant and some can be down right dangerous. I never recommend any products that Hartz or Sargent's make. I recommend Advantage II or Frontline Plus every 3 weeks for at least 4 months for indoor cats and all year round for cats that go outside. All pets in the house must be treated as if you don't the nonallergic ones serve as a flea reservoir for the allergic one and you'll never solve your problem.

Inhaled allergies (to pollens, dust mites or mold spores) are another possibility.

To control allergic symptoms (from fleas or inhaled allergens) you can try:
1) Benadryl (diphenhydramine only, the combination products with decongestants and acetaminophen are toxic to cats) at 1mg to 2mg per pound every 8 hours. That's a half of 25mg tablet every 8 hours for a cat that is 8 to 15 pounds.
2) Chlorpheniramine at 2mg to 4mg once or twice daily.
Combined with high doses of omega-3 fatty acids antihistamines work to relieve his itchiness. I like 3V caps or Derm Caps. 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 10mg to 20mg of EPA per pound of body weight per day. For example an 8 pound cat could take 80mg to 160mg of EPA per day.Together antihistamines and omega-3 fatty acids work synergistically. These should help reduce the itch. Be aware that
antihistamines can cause drowsiness or hyperactivity which should resolve with continued use.

Cool water baths with an oatmeal based shampoo can help as well, both to soothe the skin and rinse off allergens. Though the effects are temporary they can be part of the plan to help him. Make sure to wait 3 days after or give a bath 3 days before applying any topical flea products as they will be less effective if given too close to a bath.

Food allergy is another reason for excess scratching, especially of the ears, face and neck so I am glad to hear that he is on a hypoallergenic food. Though it is less likely with true hypoallergenic diets, it is possible that he is sensitive to that food now. You might wish to try a different hypoallergenic food for 8 weeks or so. Full improvement may take 12 to 16 weeks but he should be somewhat better in 8 weeks. My suggestions are Hills Z/D or Royal Canin Duck and Green peas. He will need to eat only that food, no other treats or foods during his food trial.

If there are other cats in the home that he doesn't get along with or outdoors that upset him perhaps some of this is stress related. If so a product called Feliway, which is a synthetic version of a calming feline pheromone, may help. You can purchase this from petstores or online.

If he goes outside other contagious parasites like Cheyletiella, Demodex gatoi or Sarcoptic mange are possible causes as well.

For now I would start with flea control, an antihistamine and omega 3
fatty acids. If he's not significantly better in 2 weeks then it's time for another veterinary examination to look further for problems and/or a hypoallergenic food trial.

Please let me know if you have further questions by replying to this post.
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