What you need to know about antibiotics for animals

Despite our best intentions to prevent illness using natural remedies, dogs and cats can still get sick. Here’s what you need to know about antibiotics in case your companion ever needs them.

Chances are, your dog or cat has been on antibiotics at least once in his life, perhaps for a skin problem, or an ear or urinary infection. These common medications are frequently used to treat many diseases in companion animals. While they can be life-saving, they are often used indiscriminately. In many cases, animals are given antibiotics for months to years without having even received a proper diagnosis or follow-up visit!

What are antibiotics?

Antibiotics are made from other living products such as molds. Penicillin is actually produced by the penicillium mold, as a way to prevent bacteria from killing it. In the laboratory, these raw antibiotics are chemically altered to reduce toxicity and the chances of bacteria becoming resistant to them.

Commonly used antibiotics include:

  • Amoxicillin
  • Amoxicillin-clavulanic acid
  • Ampicillin
  • Tetracycline
  • Doxycycline
  • Enrofloxacin
  • Trimethroprim-sulfa

How vets choose an antibiotic

Due to many patient and bacterial factors we can’t control, there is no “perfect” antibiotic for each animal or type of infection. Your doctor must make an educated guess as to which one is most likely to cure the disease. A number of factors allow him/her to choose the most appropriate one.

1. Knowing the disease is actually caused by bacteria, or is likely to be complicated by a secondary bacterial infection.
2. Knowing the chosen antibiotic is likely to work. This requires a current and thorough knowledge of pharmacology and pharmacokinetics. No antibiotic will kill every bacteria.
3. The antibiotic should ideally be as safe as possible for the patient.
4. Whenever possible, the least expensive antibiotic should be prescribed.

Side effects do occur

While usually safe when used on a short term basis, antibiotic therapy is not totally benign. The most commonly seen side effects include vomiting or diarrhea. This can result from a particular sensitivity to the prescribed antibiotic, or from the stomach being irritated by the medication. Giving antibiotics with food usually prevents GI irritation. However, if the antibiotic is meant to be given on an empty stomach, make sure to do so and let your veterinarian know if GI side effects occur.

While not as common as in humans, allergic reactions (such as the penicillin allergy that occurs in many people) can occasionally show up in animals taking antibiotics. Animals that have an allergic reaction to an antibiotic should not be treated with it again (or possibly with any other antibiotics in the same class of drug).

Why isn’t my animal better?

In practice, the most common side effects include a failure to improve and be “cured”, as well as an increased incidence of secondary yeast infections, common with long term antibiotic use (especially tetracycline-type medications and in pediatric patients).

There are several reasons why animals may not get better while taking antibiotics.

1. Incorrect diagnosis

Only bacterial infections respond to antibiotics, so it is important to be sure that the disease process is actually caused by bacteria. Diseases caused by viruses, fungi, and cancer will not respond to antibiotics. Additionally, most gastrointestinal problems, ear infections, vaginal infections, anal sac infections, and bladder problems in cats do not require antibiotic therapy (other than topical or local). Giving antibiotics to animals with these issues will usually not cure them as the problem is not caused by bacteria, or the systemically-administered antibiotic will not enter the infected tissue and kill the infection. Using antibiotics for these problems not only increases the cost of treatment but also the likelihood of antibiotic resistance, a serious problem in health care.

2. Underlying problems

Animals with allergies, chronic ear disease, and thyroid disease often have chronic bacterial skin infections. Some animals with chronic bladder problems have bladder stones or tumors, and some with chronic GI disease have inflammatory bowel disease. Until the underlying problem is diagnosed and treated, the tissue will continue to get infected and the animal will continue to require ever longer courses of antibiotics.

3. Wrong antibiotic

No antibiotic works all the time. If the prescribed antibiotic does not work, the diagnosis needs to be reassessed. If antibiotics are still required, a different one might be needed. Culture and sensitivity testing will help the clinician choose the correct antibiotic.

4. Wrong dose

Even the right antibiotic won’t work if it is under-dosed. While cultures can help doctors choose the most appropriate antibiotic, what happens in the animal does not correlate 100% with what happens on a culture plate in the lab!

5. Wrong treatment time

Antibiotic therapy shouldn’t be stopped just because the animal looks or feels better. Doing so will often cause a relapse due to bacteria that have not been killed but have just remained dormant. Many doctors minimize treatment time in an attempt to minimize cost. This is usually the case when treating larger dogs with skin infections, for example. Skin infections require a minimum treatment time of three to four weeks (severe and chronic infections may require six to 12 weeks). Antibiotics for skin infections are expensive; the dose for a large dog could easily cost $100 or more for three to four weeks of treatment. To help people out, some doctors only prescribe a two-week course. The animal then relapses after temporarily improving and requires more treatment, which ultimately costs more than if the animal had been treated properly in the first place.

It’s not only doctors who try to shorten treatment time when they shouldn’t. Many people commonly stop antibiotic therapy when their animals begin to “look and feel” better. Doing so will not cure the animal and may lead to a relapse that will take longer (and cost considerably more) to treat than the original infection. It’s therefore important not to stop proper therapy unless directed to do so by your veterinarian.

How complementary therapies can help

A variety of complementary therapies can be used in animals that require antibiotics. They may help reduce side effects, decrease the length of time the medication is needed, or may even be used in place of an antibiotic.

It’s important to work with a veterinarian who is well versed in both conventional and alternative therapies.


This modality uses dilute substances to treat the animal. Homeopathic “antibiotics” (called nosodes) are dilute remedies containing the bacteria for which they are indicated. For example, if the animal has a staphylococcal infection, the homeopathic doctor might prescribe the staphylococcal nosode. In effect, this is a homeopathic “vaccine” against the staphylococcal bacteria. The goal is to use the nosode to stimulate the animal’s body to attack the bacteria.

Other homeopathic remedies may be indicated depending on which part of the body is infected. For instance, animals with skin infections might be treated with the staphylococcal nosode (since staphylococcal bacteria are the primary cause of skin infections) and homeopathic sulfur, a good remedy for many skin cases. Your doctor will choose the most appropriate homeopathic remedy for your animal’s infection.


Many herbal therapies are considered “anti-bacterial” and can be tried in place of antibiotics (under a doctor’s supervision, of course). The following herbs may be helpful as your vet attempts to wean your animal off antibiotic therapy.

  • Alfalfa
  • Aloe vera
  • Astragalus
  • Blessed thistle
  • Coriander
  • Cranberry
  • Echinacea
  • Garlic
  • Goldenrod
  • Goldenseal
  • Sarsaparilla
  • Tea tree

Nutritional supplements

Olive leaf extract

This substance contains large amounts of oleuropein, which exhibits antiviral, antifungal, and antibacterial effects. It is very useful for treating animals with a variety of infections. In my practice, I use it mainly for infections of the ears, skin, and urinary systems. Feeding large amounts of olive oil will not achieve the same effect, since oleuropein is extracted from the leaves before the oil is removed for use.


Diarrhea is the most comment side effect in dogs and cats taking antibiotics. It happens because the antibiotic kills healthy bacteria and yeasts in the GI tract. These microorganisms are very important in maintaining normal bowel health. Supplementing with probiotics (usually given one to two hours after the antibiotic is given) usually prevents diarrhea.

When used appropriately, antibiotics can be life-saving. Unfortunately, they are often overused and misused, failing to cure the animal’s problem and contributing to antibiotic resistance. If your dog or cat suffers from recurring infections that don’t seem to respond well to medication, it might be time to consider a more integrative approach that encompasses alternative as well as conventional therapies.
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