Penicillin for Felines

Penicillin treats a wide range of infections in cats.
i Tabby cat taking a cat nap on a pair of shoes image by mario beauregard from

Cats get sick just like their human caretakers, and some feline illnesses require treatment with an antibiotic medication, just like you might. Penicillin is an effective, broad-spectrum antibiotic commonly used to treat bacterial infections in cats. Penicillin for felines is available only by prescription and is sold under various brand names in the United States.


Penicillin is effective against a variety of gram-positive and gram-negative bacteria. This, combined with its low-side-effect profile and broad-spectrum activity, make it a top choice for treating urinary tract infections, ear infections, respiratory infections, skin infections and soft tissue infections in cats. Penicillin antibiotics are often prescribed for cats waiting for lab results that have an obvious but unidentified infection.


Penicillin for felines is available in different forms, depending on the specific medication prescribed. Liquid preparations may be easiest to administer, but many cats are able to swallow tablets with little difficulty. The exact dose of the medication depends on numerous factors, including the weight of the cat, the type and severity of infection being treated, and the exact medication used. Typically, cats take a course of penicillin for one full week, even if symptoms improve before the week has ended.

Method of Action

Penicillin and related antibiotics work by inhibiting the synthesis of the cell walls of bacteria. This prevents bacteria from multiplying and results in their death. Penicillin is not very effective against Staphylococcus, Pseudomonas, and some strains of Serratia, Enterobacter and Klebsiella bacteria, according to The addition of a beta-lactamase-inhibitor, such as clavulonic acid, increases its effectiveness. It is effective at treating infections caused by E. coli, Streptococcus, Salmonella spp. and P. mirabilis. Do not attempt to diagnose and treat your cat without veterinary guidance; misuse of antibiotics contributes to the development of MRSA and other antibiotic-resistant strains of bacteria.

Side Effects

Gastrointestinal side effects, such as abdominal pain, reduced appetite, diarrhea and vomiting, are the most common negative reactions to penicillin antibiotics. Administering the medication at mealtimes may decrease these side effects. Allergic reactions are also possible and can cause symptoms such as vomiting, hives and excessive salivation. Additionally, long-term use of penicillin can cause an imbalance of intestinal microflora and trigger bloating, upset stomach and gas. Supplementation with a probiotic may relieve these symptoms. Report bloody diarrhea, unusual bruising, severe pain or trouble breathing to your veterinarian right away.

Always check with your veterinarian before changing your pet’s diet, medication, or physical activity routines. This information is not a substitute for a vet’s opinion.

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