Amoxicillin Allergy in Cats

Amoxicillin Allergy in Cats - Symptoms, Causes, Diagnosis, Treatment, Recovery, Management, Cost

What is Amoxicillin Allergy?

Amoxicillin for cats is a popular antibiotic for treating bacterial infections. This very effective medicine has been proven to quickly and effectively rid your cat of harmful bacteria which are the cause of infections of many types. Amoxicillin, however, has side effects, and although it is the leading prescribed antibiotic in cats, certain felines may have an allergy to this drug.

This antibiotic belongs to the same group as penicillin. It stops the bacterial growth by preventing the formation of the cell walls of these harmful, invading cells. Amoxicillin is not given for parasitic or viral infections; it is only administered for bacterial infections. 

Amoxicillin comes in specific dosages of either 250mg or 500mg capsules. The recommended dosage of this medication is to give five to ten milligrams per pound every 12 to 24 hours. This drug of choice for many veterinarians can be given on an empty stomach or with food because it is gentle on the stomach and gastrointestinal system. Only a veterinarian can prescribe this antibiotic to cats; cat owners should never give a cat the human version of amoxicillin. 

Amoxicillin allergy in cats is a result of an allergic reaction to the antibiotic. This antibiotic is used in treating a variety of bacterial infections in cats.

Symptoms of Amoxicillin Allergy in Cats

If your cat is exhibiting signs of an amoxicillin allergy, he will show you his discomfort with the following symptoms:

  • Skin rashes
  • Fever
  • Facial swelling
  • Difficulty breathing
  • Rapid heartbeat
  • Diarrhea
  • Unsteadiness
  • Confusion
  • Lethargy
  • Swelling in the limbs


There are other types of antibiotics your cat may be given if he does, in fact, have an allergy to amoxicillin. All antibiotics are unique and they are used to treat various types of infections. Your veterinarian will choose what is best for your cat. Other types of medications to treat bacterial infections include:

  • Penicillin
  • Oxacillin
  • Ticarcillin
  • Aminoglycosides
  • Cephalosporins
  • Tetracyclines
  • Erythromycin

Causes of Amoxicillin Allergy in Cats

The causes of amoxicillin allergies in cats are due to the cat’s system and reaction to the drug. Causes may include:

  • This antibiotic rids the body of harmful, as well as healthy, bacteria
  • This may result in improper digestion and passing of the food properly
  • Diarrhea may occur, which is the most common symptom
  • Amoxicillin may have an adverse reaction with other medications your cat may be taking

Diagnosis of Amoxicillin Allergy in Cats

If you have begun giving your cat amoxicillin and you see your cat having one or more of the above symptoms, contact your veterinarian. Once the veterinarian has treated your cat’s immediate symptoms and your cat is stabilized, he will ask you about any specific symptoms your cat is having and when they began. It will be very helpful to take the medication to the veterinarian with you, as in a case of an amoxicillin allergy, he would have begun showing signs after taking the medication. Your veterinarian may recommend that you have your cat tested to determine the source of the allergen.

Before this is done, however, your medical professional will take a few laboratory tests, such as blood work, urinalysis, and biochemistry profile to check his organs and how they are functioning. This will allow your veterinarian to rule out any underlying illnesses. Your veterinarian may then perform skin tests on your cat to see where the allergen is coming from. 

The doctor will apply a few items to the cat’s skin using a very thin needle. The needle will scratch the surface of the skin while applying a specific allergen. More than likely, your veterinarian will use a serum with amoxicillin on the skin test to see how the skin reacts. If your cat is having an amoxicillin allergy, he will have a reaction on the skin. Typically, the reaction will be a red bump or hives on the skin. He may also choose to check for other allergens as well; this will be discussed between you and the doctor.

If your veterinarian is concerned that your cat does, in fact, have an amoxicillin allergy, he will have you discontinue the use of the medication. He may prescribe an alternate antibiotic in its place.

Treatment of Amoxicillin Allergy in Cats

The main method of treatment is to stop giving the cat this particular antibiotic. Other treatment methods may include:

Symptomatic Care

Depending on the severity of the allergy your cat is experiencing, your medical professional will treat his symptoms. If your cat has diarrhea or is vomiting, he may choose to administer IV fluids to rehydrate him and restore his electrolytes. IV fluids also promote urination and will help flush out the antibiotic from his system. 


An antihistamine may be added to your cat’s IV in order to help his system become stabilized. This will depend on the severity of his reaction.


One treatment your veterinarian may suggest is immunotherapy. This will give you the option of building up your cat’s tolerance to amoxicillin. This will be helpful in case your cat needs amoxicillin in the future. In order to build up your cat’s immune system, your veterinarian will inject a very small amount of the antibiotic in a serum on a regular basis over time. The dosages will gradually increase, and your cat will eventually begin to experience less symptoms of an allergy. He may even show you how you can inject the treatments on your own.

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Recovery of Amoxicillin Allergy in Cats

Once you are home with your cat, your veterinarian will give you specific instructions on how to care for him. You will need to closely monitor your feline friend, and if he is taking another antibiotic in its place, this will be especially important. If your cat shows any other signs of allergies to the other medication, call your veterinarian immediately.

If you are to give your cat injections for immunotherapy, be sure to follow your veterinarian’s instructions on doing so. If you are unsure you are able to perform the immunotherapy treatment on your own, you may take your cat to the veterinarian’s office and have him do them.

Your medical professional will want to see your cat for a follow-up visit to be sure he is recovering and is responding well to any new antibiotic he may be taking. If you have any questions about how to care for your cat at home after his allergic reaction, call your veterinarian.

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© 2024 Wag Labs, Inc. All rights reserved.