Hello, my name is***** and I have over 20 years of experience as a veterinarian. I am sorry to hear that Eskarina suffers from allergies and secondary miliary dermatitis.
You can use Telfast (fexofenadine) in cats for allergic symptom relief.
The usual dose is 5mg to 10mgs of fexofenadine per kilogram of body weight once of twice daily. Usually the 60mg size is appropriate for an average sized cat, given every 12- 24 hours.
It should not be given to cats with heart disease as it can predispose to ventricular arrhythmias (irregular heart rhythms). Be careful not to give the formulations with a decongestant added as cats are very sensitive to decongestants or that contains the artificial sweetener xylitol as that sweetener is toxic for cats, leading to very low blood sugar,incoordination, collapse, seizures, liver failure and death.
Other antihistamines used to control allergic symptoms you can try include:
1) Benadryl (diphenhydramine only, the combination products with decongestants and acetaminophen are toxic to cats) at 2mg to 4mg per kilogram of body weight every 8 hours. That's a half of 25mg tablet every 8 hours for a cat that is 4 to 8 kilos.
2) Chlorpheniramine at 4mg twice daily.
3) Zyrtec (Cetirizine hydrochloride) at a dose of 5 mg per cat given orally every 24 hours. Make sure it is NOT the formulation with a decongestant (such as Zyrtec-D) because cats cannot tolerate decongestants.
Combined with high doses of omega-3 fatty acids antihistamines can work to relieve her itchiness. I like 3V caps or Derm Caps as they are reputable, high quality products. 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 her 40mg of EPA per kilo of body weight per day. For example a 4 kilogram cat could take 160mg of EPA per day. Antihistamines and omega-3 fatty acids work synergistically, better together than either one alone. These should help reduce the itch. Be aware that antihistamines can cause drowsiness or hyperactivity which should resolve with continued use.
Food allergy is another reason for excess grooming and itchy skin. You might wish to try a hypoallergenic food for 8 weeks or so. My suggestions are Hills Z/D or Royal Canin Duck and Green peas. She will need to eat only that food, no other treats or foods during her food trial.
Please let me know if you have any further questions.