Antibiotics Allergy in Cats

Written By hannah hollinger
Published: 03/26/2017Updated: 01/12/2022
Veterinary reviewed by Michele K.
Antibiotics Allergy in Cats - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Antibiotics Allergy?

Antibiotics are used in cats to treat a variety of illnesses. Antibiotics treat infections.  Although these are quite effective in treating a cat’s illnesses, there are times in which cats may show an allergic reaction to a specific antibiotic. As with other allergies, a cat’s immune system may be very sensitive to a specific antibiotic and treat the medication as a foreign substance that must be fought. As these medications are being fought by the immune system, a cat may show certain symptoms that may be a cause for concern. 

Antibiotics also have a variety of side effects that occur when taking them. Side effects from antibiotics are usually not a cause for concern if they are mild. When a veterinarian prescribes a cat an antibiotic, he will communicate with the pet owner the possibility of side effects and when to immediately stop giving the medication. An allergy, however, is different, since the cat is actually having a reaction to the medication due to an over reactive immune system rather than having a typical side effect. Side effects and an allergy may present themselves in similar forms, thus, if a cat is showing any severe symptoms, it is very important to call a veterinarian.

Antibiotics allergies in cats are due to cats being allergic to specific antibiotics prescribed by a veterinarian to fight an existing infection. Allergic reactions to antibiotics can be very mild to severe, and need medical attention.

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Symptoms of Antibiotics Allergy in Cats

If your cat is having an allergic reaction to an antibiotic, he may present a few or several symptoms. If you feel your cat is having an allergic reaction contact your veterinarian immediately. Symptoms may include: 

  • Rashes
  • Itching
  • Swelling
  • Narrowing of the airways
  • Diarrhea
  • Dehydration
  • Inability to breathe
  • Vomiting
  • Fever


There are several different types of antibiotics which cats may be given for a variety of infections. Although they are considered safe, it is important to monitor your cat when taking an antibiotic just in case he is allergic. Different types are:

  • Penicillin
  • Cephalexin
  • Enrofloxacin
  • Trimethoprim-sulfa

Causes of Antibiotics Allergy in Cats

Causes of antibiotics allergies in cats happen for several reasons and they may be confused with typical side effects. Specific causes may include:

  • Interference with other medications
  • Overdosing or dosages being too close together
  • Histamines are released within the body 
  • Immune system fighting the antibiotic as a “foreign invader”
  • Sensitive immune system

Diagnosis of Antibiotics Allergy in Cats

If you are administering antibiotics given by your veterinarian to your cat and he is showing a reaction, contact your veterinarian. Do not give your cat another dose of the antibiotic until you speak to your veterinarian.

Your veterinarian will take a close look at your cat’s symptoms and will ask you questions about when his symptoms began and the severity of those symptoms. He will want to know how many doses of antibiotics were given before he began showing signs of an allergic reaction. He may also ask if you have fed him any different types of food or if your cat has been exposed to anything different or unique which could cause an allergic reaction. Your veterinarian will perform a complete physical examination of your cat, including bloodwork, urinalysis, and any other primary tests which he feels are necessary. 

If your cat is having a skin reaction, your veterinarian may choose to scrape a tiny bit of dry skin and send it to the laboratory for a diagnosis. Typically, your veterinarian will forgo this action because of the fact your cat began exhibiting a reaction soon after beginning the antibiotic. Your veterinarian may suggest that you stop giving your cat the antibiotic and see if any allergic reaction he is having dissipates.

Your veterinarian may also suggest a different type of antibiotic for your cat so he can continue to recover from any infection he may have. He may also suggest another medication for the time being in order for your cat to begin feeling better from any allergic reaction he is suffering from.

Treatment of Antibiotics Allergy in Cats

Treatment for an allergic reaction to an antibiotic will begin once your veterinarian has determined your cat’s diagnosis. Treatment methods may include:

IV Fluids with Medication

If your cat has had diarrhea or vomiting due to an allergic reaction, your veterinarian may administer IV fluids to help rehydrate him and restore any lost electrolytes. IV fluids will also encourage urination and proper kidney function and help the antibiotic make its way out of his system so he can recover. An antihistamine may also be added to the IV to help fight the allergic reaction.

Wash and Rinse

If your cat is scratching or biting at his skin and has any inflammation or irritation of his in due to a rash or hives, your veterinarian may give him a bath using a prescription shampoo to help with any skin inflammation or discomfort. This may help calm the skin down and give your cat some relief.

Avoiding Future Dosages

Your veterinarian will likely want you to stop any future dosages of this antibiotic. Whether or not he replaces the antibiotic with another will be his decision and will depend on your cat’s infection; your veterinarian may find an alternative solution to medicating your cat so he can continue to recover from any infection he may have. Once future dosages are avoided, your cat should not have any more allergic reactions. It may take a few days for the medication to leave his system.


If your cat’s allergic reaction is severe, your veterinarian will treat him symptomatically. He may want to keep him overnight to monitor him to be sure his breathing is stabilized.

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Recovery of Antibiotics Allergy in Cats

Once you are able to take your cat home, your veterinarian will give you instructions and tell you what to watch for in terms of new symptoms. Since you are no longer giving your cat the offending antibiotic, your veterinarian may have prescribed a different medication. Once you give your cat the different medication, it will be important to understand all side effects of the medication, to give exactly the prescribed dosage, and watch for any other allergic reactions which may occur. If you see any other reactions, contact your veterinarian immediately.

Antibiotics Allergy Questions and Advice from Veterinary Professionals





Three Years


3 found this helpful


3 found this helpful

My pet has the following symptoms:
Swollen Eyes, Loss Of Appetite,
My cat recently had an exploratory surgery and was put on Veraflox, famotidine, and cyproheptadinr

Sept. 29, 2020

Answered by Dr. Michele K. DVM

3 Recommendations

Thank you for your question. Depending on the findings during the exploratory surgery, there may be an explanation for what you were describing. Since I don't know very much about your cat's situation or why the exploratory happened, it would be best to call the veterinarian that was taking care of him, let them know what is happening with him, and see what they suggest as far as treatment goes. I hope that he is okay and feels better soon.

Oct. 1, 2020

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Calico cat



6 weeks


2 found this helpful


2 found this helpful

My pet has the following symptoms:
Lethargic, Sleeping, Have To Force Feed With Bottle Cause She Has No Appetite Suddenly
Worried about our kitten she lost her mom so we have been bottle feeding her and trying to introduce dry food. She suddenly this morning not wanting to eat/drink and is tired and lethargic.

Sept. 26, 2020

Answered by Dr. Michele K. DVM

2 Recommendations

Thank you for your question. I apologize for the delay in my reply, this venue is not set up for urgent emails. It would be best to have your pet seen by a veterinarian, as they can examine them, see what might be going on, and get any testing or treatment taken care of that might be needed.

Oct. 19, 2020

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