Amoxicillin For Cats

Amoxicillin is a broad-spectrum antibiotic drug. Find out what it does and when it might be prescribed for your cat.

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Amoxicililn is an antibiotic used to treat bacterial infections. Fuse/Thinkstock

I can hear the dreaded anticipation coming through the phone lines already.

“Mrs. Banker, the test results are back, and they do confirm that Teddy has a bacterial infection,” I say. “I’d like to prescribe him an antibiotic called amoxicillin.”

Teddy, Mrs. Banker’s 12-year-old cat, presented 2 days ago with a fever and a sore front leg. He had a history of occasionally scrapping with the neighbor’s female cat, and Mrs. Banker was pretty certain that they had done battle a few days previously. Although his paw was swollen and tender when touched, there was no clear evidence of an infection at that moment. Because of this, we started Teddy on some anti-inflammatory pain medication to reduce the swelling and pain, and we also tested him for a bacterial infection to determine if antibiotics were needed.

What Does Amoxicillin Do?

So, what do we know about the medication, amoxicillin, which we were sending home for Teddy?

Amoxicillin is in a class of antibiotics called “aminopenicillins,” and is closely related to other medications you yourself may have been prescribed before, including penicillin and Augmentin. It kills bacteria by preventing their ability to put together their cell wall, which is essentially the same as the walls on your house. Without a cell wall, they can’t regulate all of the processes inside the cell, and die.

When Is Amoxicillin Prescribed?

In general, we consider amoxicillin to be a “broad-spectrum” antibiotic, meaning that it is effective against a wide range of bacteria living from many classes, including gram-positive and gram-negative bacteria. These terms refer to the color taken up by a bacterium at the time of staining, and gives the doctor some idea of the actual type of bacteria present.

To over-simplify, this term classifies the bacteria much like you would classify paper towels versus toilet paper. It doesn’t tell whether we are looking at Bounty or Brawny; but if you are looking to purchase paper towels, it will get you close enough. We use gram staining to get us to that “close enough” stage — and additional testing (called culture and sensitivity) when we actually need to get down to the details (e.g., we want to purchase Bounty Select-a-Size).

This does not mean that amoxicillin works against all infections, however. There are other organisms (such as viruses and fungi) that will not be killed by any antibiotic, including amoxicillin. Plus, there are quite a few bacteria that are not affected by amoxicillin at all. Then, there is the wild card — have any bacteria in this patient become resistant to amoxicillin?

We also have to take into consideration drug labeling. Unfortunately, when drugs are released for use on the veterinary market, they are generally made available for specific uses only. So, for example, a particular behavior drug may be released for use in dogs for the treatment of separation anxiety in conjunction with a behavior modification plan. It may work very well for other behavior problems — such as thunderstorm anxiety — but that use has not been “approved” by the licensing authorities. Similarly, the medication cannot be prescribed without combining it with a treatment plan to address the underlying behavior. Lastly, it is only labeled for use in dogs, and not for cats.

Sound complicated? Well, it is. There are ways around these requirements. For example, veterinarians can prescribe an “off label” or “extra label” use of a drug if no approved comparable drug exists. However, there is a tier of priorities.

  1. We must first use an approved drug for that condition/species.
  2. Then we can use an unapproved ANIMAL drug that we expect to be appropriate for that condition/species.
  3. Lastly, we may use a HUMAN drug under the same circumstances.

Cost is not allowed to be a factor in making the decisions of drug to use, e.g., if there is an approved drug that will cost $600 and an unapproved drug that will cost $20, veterinarians are obligated by law to prescribe the approved (but more expensive) drug. None of us like this system, and it is constantly receiving political review and debate (even at the time of publication of this article!) — so if you don’t like this system, please contact your local elected leaders, and please don’t yell at your veterinarian!

That being said, we do have to look at the labeling requirements for amoxicillin, if we are considering using it for Fluffy. According to Plumbs Veterinary Drug Handbook, 8th edition, Amoxicillin is FDA-approved for use in cats, but only for upper respiratory infections caused by three types of bacteria; urinary tract infections caused by four types of bacteria; gastrointestinal infections caused by one type of bacteria; and skin infections caused by four types of bacteria.

Even the drug formulary (our guide of what to prescribe and when) admits that, when used according to labeled instructions, amoxicillin is not considered “consistently efficacious.” It also means that the testing is supposed to be done to determine which bacteria is present before the antibiotic is used — since it is only labeled against a very small number of pathogenic bacteria.

The long story short here is that although veterinarians commonly use amoxicillin to treat a wide variety of bacterial diseases in cats, the vast majority of these uses will be “extra-label” in some fashion. This should not be translated to mean your veterinarian has done something wrong — rather that the law is written in such a limiting fashion that s/he had few reasonable choices to address the problem that your cat came in for!

So what DO we use amoxicillin for? I always prefer to use it after I have done additional testing — usually a culture and sensitivity — to tell me that the antibiotic will likely be effective against that bacteria. However, sometimes we aren’t able to afford the luxury of time to wait for those test results to come back. My most common uses for amoxicillin include confirmed:

  • Bacterial skin infections: We can see both pus and bacteria under the microscope.
  • Bacterial urinary tract infections: Again, we can see white blood cells and bacteria under the microscope.
  • Upper respiratory infections (URIs): In cats, many — if not most — of our respiratory infections are viral in nature (and not bacterial) — meaning that amoxicillin will have no effect on those infections.

Problems With Antibiotics

Antibiotics are perhaps one of the most misused, and abused, drugs commonly available today. They are only effective against problems that are caused by bacteria, and they do nothing to treat problems caused by viruses, inflammation, fungi or other causes.

Bacteria are tiny, single-celled organisms that live essentially everywhere on earth – every surface you touch likely has thousands upon thousands of bacteria living there. Most of these bacteria are friendly, and in fact, we wouldn’t have many of our favorite foods without them; and our bodies don’t work properly without a healthy colony of bacteria. However, there are a few bacteria that are capable of causing disease, and these are our “problem children.”

Unfortunately, however, when we take antibiotics, they generally aren’t able to distinguish between the good — and very necessary — bacteria in our bodies and the bad bacteria. So, we tend to kill off plenty of the little guys we really want, and need, in our bodies each time we take these medications. To make matters worse, not all antibiotics work on all bacteria — so, when we “guess” at an antibiotic, or use one randomly, we may kill off these good bacteria and completely miss the bad ones.

Now here is the real kicker. When antibiotics are not used properly — including missing doses, being prescribed too low of a dose, an antibiotic being prescribed for a non-bacterial problem, or the wrong antibiotic being used — it is possible for bacteria to develop a “resistance” to that antibiotic. This means that this particular strain of bacteria has “learned” over time how to avoid being affected by the medication in question. Making matters worse, these are very smart single-celled organisms, and they often learn how to avoid the effects of multiple antibiotic medications (as opposed to a single medication), meaning that it can be impossible to treat these infections with the antibiotics available today.

According to the Centers for Disease Control, 23,000 people die each year from bacterial resistant infections. The way we prescribe and use antibiotics has resulted in such a severe problem with bacterial resistance that people are dying without being able to be treated.

So yes, it really DOES matter what medications your pet is prescribed and how you administer them! You and Fluffy share bacteria — and if Fluffy has bacteria that have become resistant to an antibiotic, you may develop similar resistance patterns in your own bacteria.

Whenever your pet is prescribed an antibiotic, be certain that a bacterial infection has been diagnosed, and, preferably, that the testing (called culture and sensitivity) has been done to help choose the correct antibiotic. And then remember, the next stage of responsibility falls on you.

It's not always easy to give your cat medicine, but it's important that you follow the veterinarian's

It’s not always easy to give your cat medicine, but it’s important that you follow the veterinarian’s instructions. akirkman/iStock/Thinkstock

Being prescribed an antibiotic means that every dose does need to be administered on schedule, or there is an increased risk of the development of resistance. Everyone that has ever medicated a cat realizes that this is not always the easiest commitment ever, so be sure to discuss dosing forms (Is this medication available as a tablet? Capsule? Liquid? Injection? Something else?) as well as how often it must be given (once a day? Twice? Three times?) before starting the course of medication with your veterinarian.

Sometimes we do have some flexibility in medications that will work, or dosing options that will make life easier for you and Fluffy — and the best time to make these decisions is before the first dose ever hits your pet’s bloodstream.

Side Effects

As a rule, when given at appropriate doses, amoxicillin is very safe to use. The most common side effects include gastrointestinal changes (vomiting, diarrhea and reduced appetite), and some animals (as well as some humans!) will experience an allergic reaction to the medication. These reactions, although rare, can be serious. Animals taking uncommonly high doses may also experience more severe side effects, including liver value elevations and respiratory, cardiac and neurologic changes. It is capable of crossing the placenta and must be used with care in pregnant and nursing animals. There are generally no interactions of concern between amoxicillin and commonly-prescribed medications or supplements, but this should always be clarified through your veterinarian.

Forms And Dosages

The veterinary-approved formulas of amoxicillin include a liquid and tablet form. The human form also includes chewable tablets and capsules, including an extended-release capsule. The liquid form should be stored in the refrigerator. This medication appears to be largely palatable to cats, and most owners seem to be able to administer it without an unusual degree of difficulty.

Dosing decisions can be challenging. Remember again, the labelled directions already include an accepted dose, so any variation from that will be considered “extra-label.” Most veterinarians consider the labelled dose to be too low to be effective, so it is very common that a higher dose will be prescribed. These decisions are often made taking into consideration:

  • the severity of the infection,
  • the suspected (or confirmed) bacteria present,
  • the length of time the infection has been present,
  • the location of the infection (some parts of the body are easier for the blood — and hence medication — to access, so a lower dose can be used), and
  • the overall health of the patient.

Young animals, as well as those that are debilitated, may need to have their doses adjusted to achieve the desired effect without causing side effects. Although it is something that is done multiple times per day, which antibiotic — and at what dose — actually has a lot of variables factored into it by the veterinarian. Remember, though, the medication only works as intended when it makes it into the patient on schedule!

So, why did we decide to use amoxicillin for Teddy, Mrs. Banker’s cat? Firstly, we had sent out a culture and sensitivity test when Teddy first came in. This showed that he was infected with Staphylococcus aureus, and that his particular strain of bacteria was indeed sensitive to amoxicillin. Skin infections caused by S. aureus are indeed an approved use for amoxicillin in the cat. However, the FDA-labelled dose, in my clinical opinion, was too low to be effective at this particular infection site (the paw) in an older animal. So, I prescribed a higher dosing frequency than is labelled (amoxicillin is labelled for once per day, and I prescribed it for twice per day), essentially doubling the dose Teddy would receive.

When Teddy came back for his recheck appointment 10 days later, everything was healed and he looked super, having experienced no side effects from the medication. Mrs. Banker found the medication easier to administer than she had expected, and everyone left happy — except Teddy. Mrs. Banker had decided to keep him indoors going forward to help avoid any future squabbles with the neighbor’s cat. Poor Teddy, but he will be healthier that way!

Article Categories:
Cats · Health and Care

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