Should a Pet Be Off Antihistamines or Steroid Before Allergy Testing?

Should a Pet Be Off Antihistamines or Steroid Before Allergy Testing?

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Dr. Debra,

My dog has severe allergies. I’ve thought about doing allergy testing but could not decide. He is a 3-year-old Labrador and he suffers from ear infections, skin infections and constant itching.

He has been off and on antibiotics, steroids, and antihistamines for the past 2 years. It seems like he does better on these drugs, goes off then breaks out again.

If I go ahead and do allergy testing – does he need to be off the steroids, antihistamines and antibiotics prior to allergy testing?

Connie B., Norfolk, VA

Hi Connie,

Thanks for your excellent question. Allergies in dogs are so frustrating for both you and your dog. As you said is the case with your dog, many dogs are treated with antibiotics, antihistamines and/or steroids to control the symptoms and once you go off, the symptoms come back.

Many types of antibiotics are used to treat canine skin infections. Antihistamines used in dogs may include: Benadryl, Zyrtec, Chlortabs, or Allegra just to name a few. Steroids may include injectable or oral medications including Prednisone or Dexamethasone to name a few. They are often used together to try to control allergic symptoms. The term used for being off the drug is called the “withdrawal time”.

To answer your question – “Does your dog need to be off steroids, antihistamines and antibiotics prior to allergy testing ” – here is the answer.

There are two basic types of allergy testing. One is an intradermal test and the other is a blood test. For more information – go to: allergy testing in dogs.

The recommendations for how long a dog needs to be off a drug depends on the drug being used, how often that drug is given and the type of allergy testing your dog is going to have.

  • Antibiotics – There is no required withdrawal time for antibiotics.
  • Antihistamines – Based on my discussions with dermatologists, they recommend discontinuing oral antihistamines 1 to 2 weeks prior to Intradermal skin tests in dogs or cats. For dogs getting Allergy Testing (IgE serological tests), many dermatologist indicate that it is not necessary to discontinue antihistamines prior to testing.
  • Steroids – For steroid drugs, there are different types of steroids and some last longer in the blood than others. The type of steroid and how frequently they are used can affect testing. For example, a steroid that lasts longer but only given once may have less issues with testing than a shorter acting steroid given regularly.

A withdrawal time is the amount of time a dog or cat needs to be off the drug (the drug is withdrawn from their system) prior to testing:

Drug Withdrawal Times for Intradermal Skin Tests

  • Oral Steroids

    • Prednisone – 14 – 21 days
    • Triamcinolone – 21 days
  • Injectable Steroids
    • DepoMedrol – 1 – 3 months
  • Other
    • Oral antihistamines – 14 days
    • Cyclosporine – depends on dermatologist but many say no withdrawal time is needed
    • Fatty acids – no withdrawal
    • Vitamin E – no withdrawal
    • Apoquel – no withdrawal
    • Antibiotics – no withdrawal
    • Antifungal drugs – no withdrawal

Drug Withdrawal Times for Allergy Testing (IgE serological tests)

  • Oral steroids

    • Prednisone – 45 days (if the dose is > 0.25 mg/kg)
    • Prednisone – 21 days (if the dose is < 0.25 mg/kg)
    • Methylprednisolone – 45 days
    • Triamcinolone – 60 days
  • Injectable steroids
    • Triamcinolone – 60 days
    • Methylprednisolone – 90 days
  • Topical steroids
    • Otic and ophthalmic preparations – 30 days
    • Steroid shampoos – 30 days
    • Sprays – 30 days
  • Other treatments
    • Cyclosporine >30 days – contact vendor performing test (However some resources do say there need be no withdrawal time)
    • Antihistamines – Most say no withdrawal (However some resources do say 2 weeks)
    • Fatty acids – Most say no withdrawal (However some resources do say 2-4 weeks)
    • Vitamin E – no withdrawal
    • Apoquel – Most say no withdrawal (However some resources do say 48 hours)
      Antibiotics – no withdrawal
    • Mometamax- (ear medication) 7 days

Many dogs with allergies when tested end up having allergies to multiple things including fleas, pollens, weeds, mold and food.

Here are some helpful articles:

Atopic Dermatitis in Dogs
Flea Allergy Dermatitis in Dogs

IMPORTANT – please check with your veterinarian for the individual
requirements based on the lab they are using. Every lab has slightly different recommendations on withdraw of the various drugs. The above is what I use from the laboratory I used and based on my conversation with various dermatologists.

Best of luck,

Dr. Debra

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