Amoxicillin For Cats: Dosage, Safety & Side Effects

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Amoxicillin for cats feature

Amoxicillin is a common antibiotic prescribed for both cats and dogs to address a variety of bacterial infections. Amoxicillin has many brand names as well as generic forms.

Amoxicillin For Cats Overview

Medication Type:
Tablet, Liquid
Prescription Required?:
FDA Approved?:
Common Names:

In this article, you’ll learn what amoxicillin is, the types of infections it may be used for in cats, potential side effects, and some other useful info and frequently asked questions.

What Is Amoxicillin?

Amoxicillin is an antibiotic called an aminopenicillin. As a bactericidal antibiotic, it has the ability to kill certain strains of bacteria causing infections.

Amoxicillin may be used for infections of the respiratory tract, urinary tract and bladder, some gastrointestinal infections, and infections of the skin and soft tissues. Because there are many antibiotics out there, a veterinarian should always be responsible for deciding which one is best to use for a particular patient.

Because amoxicillin-clavulanate, commonly known as the brand Clavamox, has a broader spectrum of action against some bacteria, it is more commonly used than regular amoxicillin, especially for cats.

What Does Amoxicillin Do For Cats?

use of amoxicillin for cats

As a bactericidal antibiotic, amoxicillin works to kill bacteria associated with upper respiratory infections, urinary tract infections, and more.

As a bactericidal antibiotic, amoxicillin has the ability to kill certain kinds of bacteria causing infections.

In kitties, it may be used most often for upper respiratory infections, urinary tract infections, skin infections, or infections resulting from a bite wound or injury.

Amoxicillin works by binding directly to certain parts of the cell membrane of susceptible bacteria, inhibiting development of the cell wall and making the bacteria unstable, thus killing them.

It’s very important to note that amoxicillin is not effective against viral infections, a common cause of upper respiratory conditions in cats. Therefore, it’s always important for a vet to decide if use of an antibiotic is warranted.

Side Effects Of Amoxicillin For Cats

Side effects of amoxicillin for cats

The side effects of amoxicillin are usually mild and infrequent, involving gastrointestinal upset like vomiting and diarrhea.

Side effects of amoxicillin in cats are typically mild and infrequent but when they do occur, most often include digestive upset, like vomiting, diarrhea, and a decrease in appetite.

Oral amoxicillin, like many broad-spectrum antibiotics, can alter the normal, beneficial bacteria in the digestive tract, which is often a cause of digestive upset if it occurs.

Giving amoxicillin to your kitty around the time of a meal can help to offset these possible effects. If side effects like these continue, it’s important to ask your vet for further advice.

While discontinuing an antibiotic may relieve the side effects, this will also leave the original bacterial infection untreated. If your kitty is dealing with a very concerning infection, your vet may, for example, recommend starting a probiotic as opposed to discontinuing an antibiotic.

Also Read: 10 Best Probiotics For Cats

Severe allergic reactions to amoxicillin are extremely rare but can include rashes, hives, fever, and changes to red and white blood cell counts. To the rare kitty this might happen with, these effects would occur with even a very small dose. In other words, if your kitty is doing well at a prescribed dose, an accidental extra dose or overdose would not cause these effects.

Amoxicillin For Cats Dosage

Dosage of amoxicillin for cats

Follow the dosing instructions provided by your veterinarian. Most vets call for a dose every 8-12 hours.

Interestingly, the labeled dosage for cats for amoxicillin calls for giving it just once a day. However, this dosage is generally no longer considered in veterinary medicine to be effective for most infections.

Most vets are using it off-label at every 8-12 hours, similar to the labeled dosage for dogs. If your vet decides to use amoxicillin for your cat, he or she will decide on a recommended dosage amount and schedule that is most appropriate depending on the type of infection being addressed.

Amoxicillin typically comes in both a liquid form as an oral suspension as well as tablet form. Your veterinarian may have a preference of which form to use, or may leave the dosage form up to you depending on which will be easier to administer.

If your kitty will take a pill mixed with or hidden in food or a treat, this is often easiest and involves the least amount of struggle. However, if your furry friend is the type that will eat everything in the bowl but the tablet and leave it at the bottom, you may need to consider liquid if you are not adept at administering a pill directly into your cat’s mouth for her to swallow it.

The liquid form typically needs to be refrigerated. It is often reconstituted with water at your vet’s practice when you receive it. If your vet prescribes two bottles, they should provide you with instructions on how to mix up the second bottle. Because liquid amoxicillin should be discarded after 14 days, it is important not to mix up a new bottle until you are ready to use it.


Amoxicillin is one of the oldest, tried and true antibiotics we have and although newer antibiotic classes have been developed, amoxicillin still has valuable clinical uses.

However, it’s really important to make sure it is only used when dispensed or prescribed by a veterinarian, and that all prescribing instructions are followed. Indiscriminate use of any antibiotic can lead to resistant bacterial populations, which make treating infections more difficult.

Always make sure to give an antibiotic prescribed by your vet for the full number of days indicated, even if your kitty looks like he’s feeling better.

Frequently Asked Questions

Is Cat Amoxicillin the Same as Human Amoxicillin?

Amoxicillin comes in a liquid suspension, tablet, and capsule forms. The most common form given to cats is the liquid suspension or the tablets, both in specific veterinary preparations.

While human amoxicillin is actually the same medication, the dosage forms available for people may be problematic for use with cats. The lowest tablet dosage for people of 125mg will be much too high for most cats. 

The generic human liquid suspension could be used, however the volume of medication in some available preparations may be far more than what is needed for a cat’s typical dosage period, making them less practical.

How Long Does Amoxicillin Take to Work in Cats?

For susceptible bacterial infections, you will typically see noticeable improvement within 2-3 days of use. Full resolution for an infection depends a lot on the location and severity. This is why it’s always important to follow the prescribed directions and to finish out all of an antibiotic even if your kitty is looking much better.

Is Amoxicillin Poisonous to Cats?

Amoxicillin is not poisonous to cats, is very safe at prescribed doses, and side effects are uncommon.

However, if a cat were to get into and consume an amount of amoxicillin much higher than a typically prescribed dosage, like say, a 500mg human tablet, severe digestive upset may occur. Neurologic changes, like an inability to walk normally (termed ataxia) have been reported in dogs, as well as elevated heart rate and breathing changes.

Many medications can cause significant negative health effects if very high doses inappropriate for the patient are ingested. So while amoxicillin is not in itself a toxin, if you suspect your kitty has ingested an overdose of her own amoxicillin or possibly any prescribed for you or a family member at home, always notify your veterinarian and/or get in touch with Animal Poison Control to determine what steps may need to be taken.

How Much Amoxicillin Do You Give a Cat?

In short, what your veterinarian prescribes! Amoxicillin has a wide dosage range. The dosage and frequency can vary depending on the type of infectious condition being treated, so it’s always best for your kitty’s vet to determine what is most appropriate. 

And always remember that even if your kitty appears to be feeling better, to always finish out a prescribed course of antibiotics, as this helps to reduce the risk for development of bacterial resistance to antibiotics.

About Dr. Chris Vanderhoof, DVM, MPH

Dr. Chris Vanderhoof is a 2013 graduate of the Virginia-Maryland College of Veterinary Medicine (VMCVM) at Virginia Tech, where he also earned a Masters in Public Health. He completed a rotating internship with Red Bank Veterinary Hospital in New Jersey and now works as a general practitioner in the Washington D.C. area. Dr. Vanderhoof is also a copywriter specializing in the animal health field and founder of Paramount Animal Health Writing Solutions, which can be found at Dr. Vanderhoof lives in the Northern Virginia area with his family, including 3 cats.

4 thoughts on “Amoxicillin For Cats: Dosage, Safety & Side Effects

  1. Janay Bonforti

    I feed ten feral cats friskies canned cat food. Once a month I open two fish amoxcillin capsules and blend it in with their food. Should I be doing this because it takes care of their worms.

  2. Dr. Chris Vanderhoof, DVM, MPH Post author

    Hi Janay,

    Firstly, thanks so much for being a caretaker for a feral cat population. Those outdoor kitties need our help too.

    But unfortunately, I would feel that the addition of the fish amoxicillin capsules is misguided for two reasons. One, you mentioned that amoxicillin will address “worms”. By that, I assume you’re referring to intestinal worms like roundworms, hookworms, or tapeworms, which these kitties could certainly have. Amoxicillin has no effect against worms in any way, only against bacteria, as I mentioned in the article, so the amoxicillin you’re adding would not be helping with the problem you’re trying to address.

    Two, fish amoxicillin is designed to be added to the water of a fish tank and absorbed by fish. Fish amoxicillin is not intended to be used for other species of animals and it is in fact, not the same strength or formulation as what we use for pets or even people. Additionally, and perhaps surprisingly, the reason you can purchase fish amoxicillin over the counter is that it is not regulated by the FDA at all. This means there could be a lot of variability in the quality and manufacture.

    Adding the fish amoxicillin capsules to the feral colony’s canned food is unlikely to be providing any significant benefit, and is more likely to be contributing to amoxicillin-resistant bacteria. This could mean that if one of the kitties truly became ill, a medication like Amoxi-Drops or Clavamox may not be as effective as it would otherwise be.

    I do not work with any feral populations myself, but it has been my understanding that there are often local vets that are willing to help keep these outdoor kitties as healthy as possible. Hopefully, there may be a vet in your area that could help provide some more specific guidance.


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