Clavacillin is a veterinary antibiotic used in cats to treat skin and soft tissue infections, including wounds, abscesses, and cellulitis, as well as urinary tract infections. It combines two active ingredients: amoxicillin, which kills bacteria, and clavulanic acid, which prevents bacteria from defending themselves against the antibiotic.
Infections Clavacillin Treats in Cats
Clavacillin is FDA-approved for two main categories of feline infections. The first is skin and soft tissue infections: wounds, abscesses, and cellulitis or dermatitis caused by susceptible bacteria. Cat bite abscesses are one of the most common reasons a vet will prescribe it, since outdoor and multi-cat households see these frequently. The second approved use is urinary tract infections (cystitis), particularly those caused by E. coli.
The drug targets several bacterial species that commonly infect cats, including Staphylococcus, Streptococcus, E. coli, and Pasteurella. That last one matters because Pasteurella is a normal inhabitant of cats’ mouths and a frequent culprit in bite wound infections.
Veterinarians also prescribe amoxicillin-clavulanic acid (the same drug combination sold under different brand names) off-label for upper respiratory infections in cats. Secondary bacterial infections with Pasteurella, Staphylococcus, Streptococcus, and Bordetella commonly develop on top of viral respiratory illness, and lab testing shows the drug is effective against all of these organisms. While this use isn’t part of the official label, it’s a well-established practice in veterinary medicine.
How Clavacillin Works
Amoxicillin belongs to the penicillin family and kills bacteria by breaking apart their cell walls. The problem is that many bacteria have evolved an enzyme that disables penicillin-type drugs before they can do their job. This is one of the most common forms of antibiotic resistance.
Clavulanic acid solves that problem. It binds to the bacterial enzyme with a stronger grip than amoxicillin does, permanently disabling the enzyme so amoxicillin can work unimpeded. Clavulanic acid has almost no bacteria-killing power on its own. Its entire role is protecting amoxicillin from being neutralized. This combination gives Clavacillin a broader reach than amoxicillin alone, making it effective against resistant strains of Staphylococcus aureus and other bacteria that would otherwise shrug off a standard penicillin.
Available Forms and Typical Dosing
Clavacillin comes in two forms for cats: chewable tablets and an oral liquid suspension (drops). The liquid version is often easier for cat owners to administer. It contains 50 mg of amoxicillin and 12.5 mg of clavulanic acid per milliliter.
The standard recommended dose for cats is 62.5 mg given twice daily, which works out to 1 mL of the liquid suspension per dose. Your vet may adjust this based on your cat’s weight and the type of infection being treated. The liquid suspension needs to be kept refrigerated and has a limited shelf life once mixed, so check the expiration information on the bottle.
How Long Treatment Lasts
For skin and soft tissue infections like abscesses and cellulitis, the typical course is 5 to 7 days, or until 48 hours after all symptoms have cleared, whichever is longer. Treatment should not exceed 30 days. If your cat shows no improvement after 3 days, the prescribing guidelines recommend stopping the medication and reassessing, since the bacteria involved may not be susceptible to this drug.
Finishing the full course matters even if your cat seems better after a couple of days. Stopping early increases the chance that surviving bacteria rebound and cause a harder-to-treat infection.
Side Effects to Watch For
The most common side effects in cats are digestive: vomiting, diarrhea, and reduced appetite. These are typical of penicillin-type antibiotics and usually mild. Giving the medication with a small amount of food can help reduce stomach irritation, though you should follow your vet’s specific instructions on timing.
Allergic reactions are possible in cats with a sensitivity to penicillin-type drugs. Signs of an allergic reaction include facial swelling, hives, difficulty breathing, or sudden vomiting. Cats with a known penicillin allergy should not take Clavacillin.
Animals That Should Not Take Clavacillin
Clavacillin should never be given to rabbits, hamsters, guinea pigs, or other small rodents. In these species, the drug disrupts gut bacteria so severely that it can cause life-threatening diarrhea. This is worth knowing if you have multiple pets in the house, since a cat’s leftover medication could be dangerous to a small animal that accidentally ingests it. Store the medication securely and never share prescribed antibiotics between different species.