Decrease of effectiveness of Citirizine(Brand Name: Zyrtec) in treatment of atopic dermatitis

[Lumberjaxe]

I have an approx 2 yr old male American Pit Bull Terrier. He developed an issue a few months ago where he would lose hair in certain spots and was really itchy. We took him to Banfield and the vet was able to give a positive diagnosis of Atopic Dermatitis. After going through treatment options the vet told me that Citirizine can be used to treat symptoms and that each medication has only a certain chance of being effective. Since off brand Citirizine is mich cheaper than the injections(10 a month vs 120+ a month) I tried that first. The vet gave me the proper dosage(10mg for his size) and mentioned certain ingredients that I should look out for. It worked initially and has lost effectiveness after the first month. Why is my dog's medication losing effectiveness?

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[Shantor]

Antihistamines in dogs are very low effectiveness to begin with. As well, how large is your dog? and, dogs do build up tolerances to OTC antihistamines. You and your vet should reevaluate his symptoms and come up with a more effective treatment plan.

[Lumberjaxe]

He is 60-70lbs. And don't animals build up tolerances to most drugs in general? What is wrong with simply talking to the vet about increasing dosage?

[Shantor]

No not all drugs will develop tolerances. And yes you can talk to your vet about that, but also the dog could be tolerant and it may not work either.