Common side effects of cefazolin are vomiting or diarrhea after a treatment. These symptoms are not normally serious, but are a sign that your pet is sensitive to the drug. Cefazolin can cause sensitivity or pain at the injection site, or a sterile abscess. Animals that are hypersensitive to drugs of this type might experience anaphylaxis, rashes, fevers, and blood changes. Kidney damage is an uncommon side effect, and usually only occurs in pets with kidney problems to begin with. High doses, or prolonged treatment, can result in neurotoxicity, neutropenia, agranulocytosis, thrombocytopenia, hepatitis, interstitial nephritis, positive Coomb's test, or tubular necrosis.