Pet Care Advice 》 Antibiotics

  What are antibiotics? 

It is quite common for dogs to suffer from bacterial infections and diseases, so we often need to use antibiotics. Bacteriostatic antibiotics inhibit the multiplication of bacteria, while the bactericidal antibiotics kill the bacteria, but in nearly all cases with antibiotics, they switch between being bactericidal and bacteriostatic depending on the concentration.  

Antibiotics can be seen in a form of capsules, chewable tablets, ointments and liquids, and a responsible pet owner should know the effect of antibiotics on your pet.

Bacteria come in different shapes and sizes, and it is those physical characteristics that help your veterinarian determine which bacteria are infecting your animal. Responsible for gastroenteritis, pneumonia, skin infections, urinary tract problems, and a host of other diseases, these tiny, one-celled organisms can sometimes outsmart the immune system and multiply unchecked in your pet's body without the intervention of antibiotics.

By affecting biochemical pathways that are unique to bacterial cells and not seen in animal cells, bacterial antibiotics are able to work to destroy the offending cells while leaving your pet's healthy cells intact. Depending on the medication, an antibiotic might inhibit the bacterium's ability to construct cell walls, thus destroying its ability to reproduce. An antibiotic can also starve the bacterium by stopping its ability to transform glucose into energy, which is a major function of all living cells.

Antibiotics are usually harvested from moulds and other bacteria that create them naturally so they can defend themselves from being over run.  This is how penicillin came to the attention of the researchers, the mold secreted a substance that stopped bacteria growing near it.

  Antibiotic resistance

A lot is talked about antibiotic resistance and it has been a concern for the last thirty years or more, and the constant threat is that we will have no antibiotics to treat some infections.

The opinions of how and when they should be used change over time and between people.  Current thinking about infections go along these lines:

An infection starts with a few bacteria that hide from the host and don't present any noticeable issues, so the host does not do much about them.  When the bacterias build up, they are more active and release toxins and enzymes that damage the host tissues.  When the bacteria become more numerous they develop a biofilm, which is essentially slime, made up of DNA from dead bacteria and mucin.  This helps protect the bacteria from the hosts immune system, and allows the ones in the centre to continue to breed and excrete toxins and generally become more virulent.

This is why the opinion in leading hospitals has changed from not using antibiotics unless absolutely necessary to using them in high doses for a short period when an infection is suspected, or in the immediate post-operative period.

Antibiotic resistance comes about when low doses of antibiotics are given over a prolonged period, so allowing the naturally resistant bacteria to grow and prosper.  This is why it's better to catch the infection early, weigh the animal to get an accurate dose, then give a suitable antibiotic at a therapeutic level for as short a period as possible to resolve the infection.

  Common antibiotics for pets:

Some of the more common antibiotic medications that are prescribed to dogs are:

Cephalosporins - Cephlexin

This class is related to the pencillins, but have additional mechanisms of action that are not well understood.  They are mainly used to treat bacterial infections, along the lines of those that could develop in a cut or broken bone, as well as sometimes being used for treatment of bladder-related infections.

Fluroquinolones - Enrofloxacin, Marbofloxacin etc

Mainly used for respiratory, skin, and urinary tract infections.  They penetrate fat quite well.

Macrolides – Lincomycin, Clindamycin, Steptomycin etc 

This includes middle ear infections, bone or joint infections, pelvic inflammatory disease, pneumonia, and endocarditis among others.


An antibiotic that is used to treat a wide variety of anaerobic and protozoal infections. This antibiotic treats only certain bacterial and parasitic infections. Like all antibiotics, it will not work for viral infections (such as common cold, flu).

Penicillins - Amoxicillin, Penicillin, Ampicillin

This antibiotic is mainly used to treat skin and tissue infections, as well as being prescribed to tackle respiratory and gastrointestinal infections. Amoxicillin combined with Clavulonic Acid is a more effective version of this drug, as the Clavulonic Acid competitively inhibits an enzyme (unimaginatively, but helpfully called penicillinase, but also known as beta lactamase) secreted by resistant bacteria that breaks down penicillin.  Because acquired resistance to this drug combination is rare, it is used frequently by vets.

Tetracyclines – Oxytetracycline, Doxycycline etc.

This group are bacteriostatic at normal concentrations, and because many other antibiotics need dividing bacteria to be effective, in general the tetracylines are given by themselves.  Especially useful for respiratory infections and intracellular organisms.

  Advice on dog antibiotics over the counter without a prescription and its side effects 

Although rare, adverse effects of antibiotic therapy can occur.  Most oral antibiotics will cause nausea and sometimes vomiting and diarrhea.  Owners should be aware of these potential side effects.  Metronidazole can cause neurological problems even at normal therapeutic doses, and should be stopped and veterinary advice sought as soon as these are observed.

  Antibiotics for skin infections 

When a dog's skin is cut or wounded, there is an increased risk of infection. Pyoderma is a deep bacterial skin infection that is very common in dogs. Lesions and pustules (inflamed pus-filled swelling) on the skin, and in some cases partial hair loss, often characterize the infection. Treatment is typically given on an outpatient basis and prognosis is good.

The infection typically responds favorably to medical treatment. Treatment is generally done on an outpatient basis and will involve external (topical) medications, as well as antibiotics for the infection.

An antibiotic treatment regimen is generally prescribed for a minimum of 10 days, but can often be for a month or more to ensure that the entire infection is eliminated from the dog's system, which should also reduce the incidence of recurrence.  To see if an infection has cleared from skin, pinch a fold between thumb and forefinger and assess the thickness; it should be the same as the surrounding skin if the infection has resolved.

  What are "natural" anti-biotics? 

Studies on farm animals have also shown that antibiotic use leads to an increase in antibiotic resistance in animals taking the drugs as well as in people working on the farms where those animals live. Even when farmers stop using the drugs, resistance persists for years, as mothers pass their drug-resistant flora down to their offspring for generations.

Fortunately, there are natural alternatives to antibiotics. Instead of using antibiotics as a first line of defense, in farm animals, better husbandry including vaccination, nutrition and ventilation can help stop or eliminate herd infections. 

For small animals, in some cases it may be appropriate to try one of the many natural options available. They can be quite effective and they just might help your dog avoid antibiotic resistance and toxemia that can be caused by antibiotic use. Some examples of natural antibiotics include garlic, bee propolis and wheat.  However, much of the evidence supporting the use of these in serious infections is weak so they should not be relied upon in serious infectons. It is always best to consult your veterinarian who can provide expert advice.