The Side Effects of Antibiotics in Cats

Updated April 17, 2017

Just like humans, cats develop infections that need to be treated with antibiotics. Often they are even treated with a lower dose of the same medications given to humans. These medications include antibiotics of the penicillin class, aminoglycosides, cephalosporins, tetracyclines and erythromycins. cautions that although antibiotics are very effective in treating a cat's infection, they also come with some painful side effects.


The possibility of an allergic reaction is a shared side effect of all antibiotics. Because antibiotics are derived from bacterial moulds, cats may share the same sensitivity to them (particularly penicillin-based ones such as amoxicillin) that humans do. Doctors Foster and Smith report the indications of an allergic reaction are facial swelling and/or hives, diarrhoea, vomiting, and the more severe symptoms of shock, seizures, pale gums, cold limbs and a comatose state.

Loss of Hearing

Hearing loss is a rather unusual and concerning side effect of the use of an aminoglycoside antibiotic, according to In fact, Doctors Foster and Smith warn that kanamycin, a form of aminoglycoside antibiotic approved for use in the both cats and dogs, should not be used in guide animals as hearing loss might be irreversible. While it is highly unlikely that a cat would be trained as a guide animal, the risk of hearing loss is still present when these types of antibiotics are prescribed to the feline.

Liver or Kidney Disease

Some antibiotics can cause serious side effects such as liver or kidney disease in cats. A side effect of amoxicillin is liver disease indicated by jaundice. Tetracycline should not be administered to cats with liver or kidney disease warn Doctors Foster and Smith, who also advise using caution in prescribing erythromycin to cats with liver disease.

Fur Loss and Photosensitivity

Both tetracycline and erythromycin can cause a cat to lose its fur and become sensitive to sunlight. According to Doctors Foster and Smith, you should protect your animal from exposure to the sun, particularly when using tetracycline, as uncovered skin may break out in blisters and pustules.

Diarrhoea and Vomiting

Perhaps the most common side effect of any antibiotic prescribed to a cat is vomiting and diarrhoea. While this may be a sign of an allergy to the prescribed medication, vomiting and diarrhoea may also be indicative of simple stomach upset that can be aided by giving the medication with food when recommended.


Mar Vista Animal Medical Center reports that cephalexin, an antibiotic of the cephalosporin class commonly prescribed for skin infections, may cause fever in felines. Mar Vista recommends discontinuing cephalexin immediately should the cat develop a fever and consult the cat's veterinarian who should prescribe a different antibiotic.

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