Skip to main content

Reasons Why Dog Antibiotics are Not Working

Dog Antibiotics

If your dog has not been feeling well, you may be concerned about those dogs antibiotics not working as they should. The success of a course of antibiotics depends on a variety of factors. All it takes is for one or more of these factors to take place, and you have a case of antibiotics failing to wipe out and infection. If your dog's antibiotics don't seem to be working, it's important that you consult with your vet to determine the underlying cause. Following are some reasons why your dog's antibiotics may not be working as they should.

Apoquel for dog allergies

The Goal of Antibiotic Treatment

The main goal of successful antibiotic treatment is to administer the affected dog a sufficient dose of antibiotic to kill the bacteria or at least to suppress the bacteria enough so that the dog's immune system can kick in and take over the task of killing bacteria and overcoming the infection.

However, not always everything goes as planned. After antibiotics are started, they may not be effective at all or they may fail to reach concentrations that have the power to kill bacteria. Veterinarians rely on some guidelines to ensure that antibiotics work as they should.

The minimum inhibitory concentration (MIC) is the the lowest concentration of the drug needed to inhibitbacterial growth. The minimum bactericidal concentration (MBC), also known as the minimum lethal concentration (MLC), is instead the lowest concentration of the drug that is needed to kill 99.9 percent of bacteria. The minimum antibacterial concentration (MAC), on the other hand, is the lowest concentration of the drug needed to interfere with the bacteria's ability to proliferate, however it does not kill the bacteria.

These factors are considered in veterinary medicine so to heighten the chances of success in antibiotic treatment. It's important for your vet to know the exact weight of your dog considering that dosages for antibiotics are based on your dog's weight to ensure your dog receives an effective concentration of antibiotics so to kill the bacteria.

[otw_is sidebar="otw-sidebar-1"]

Why are My Dog's Antibiotics not Working?

Despite these guidelines that help veterinarians make out the most for the most appropriate treatment plan for dogs in need of antibiotics, antibiotics may fail at times, and it's important figuring out why this may be happening, with the help of the vet.

Poor Owner Compliance

One of the primary reasons antibiotics may not be working is because dog owners may not be following the label instructions carefully. Owners may forget to give the antibiotic, often skipping days or altering the frequency of administration, which may lower the bactericidal concentration needed in order to kill the bacteria.

One common problem encountered is dog owners who stop the antibiotics early instead of finishing up the bottle as instructed on the label. It may be tempting to stop the antibiotic early as soon as the dog seems to get better, but this is a big mistake as it gives the bacteria the opportunity to make a come-back paving the path for a potential recurrence requiring a stronger antibiotic.

A Matter of Antibiotics

Not all antibiotics are created equal and not all bacteria are the same. If your dog's infection is not getting better by the day, there are therefore chances that he may need a different antibiotic.

Not giving the right antibiotic is often a matter of dog owners who feel tempted to skip the veterinarian and self-treat at home giving antibiotics prescribed for humans, which may not always be appropriate or are perhaps are even expired or stored improperly. Depending on the location of the infection, some antibiotics may have a hard time penetrating a specific type of tissue or the antibiotic may be ineffective in killing a particular strain of bacteria.

If the antibiotics were prescribed by your vet and you are giving them exactly as prescribed and they are not working, there are chances your vet may need to do a culture and sensitivity test to determine exactly what bacteria are present and which antibiotics work best to combat these.

Scroll to Continue

Discover More


Do Dogs Act Out of Spite? Here's What Science Says

Whether dogs act out of spite is an important question considering that spiteful behavior can put a big dent in your relationship with your dog. If your dog appears to pee, poop or destroy things out of spite, this is article is ultimately for you.


What Does it Mean for a Dog to "Honor The Point?"

A dog honoring the point, may sound like something quite complex, but in the world of hunting dogs, this term is quite popular. Discover what honoring means in dogs and the importance of a dog honoring another dog's point.

Screenshot 2022-06-24 152828

Examples of Stereotypical Behaviors in Dogs

If you are looking for examples of stereotypical behaviors in dogs, most likely you have heard about stereotypies and are looking for some concrete explanations. Discover in layman terms what stereotypies are in dogs along with several examples.

Generally, prescribing broad-spectrum antibiotics such as Clavamox from the get-go is a good ideas because these antibiotics cover a wide variety of bacteria, but there might be circumstances where the vet may prefer prescribing other types. Some conservative vets may elect to use the narrower-spectrum types because they can do the job and help prevent antibiotic resistance.

Incorrect Diagnosis


In the medical field there is a saying "if you hear hoofbeats, think horses and not zebras." What does this mean? It means that if a patient has a sneeze and the sniffles, the doctor will treat it as a cold instead of treating it as a rare tropical disease that is very unlikely to happen.

So if your dog presents with some distinct symptoms, your vet may assume he's dealing with a common condition rather than some other rare, uncommon condition that is less likely. Most vets generally do not like doing "guesswork" but sometimes they are forced to because of financial constraints of dog owners who cannot afford paying for an expensive battery of tests.

Antibiotics may therefore be prescribed as a tentative diagnosis of exclusion. In other words, if the dog responds well to the antibiotics, then that proves to the vet that the dog was truly dealing with an infection and once the dog heals, the chapter is closed. However, at times, the chapter remains open, and the vet must sort through other possibilities. For example, if your dog has a skin infection and doesn't get better on antibiotics, there may be chances that the infection is fungal rather than bacterial or if your dog's antibiotics are not working for a UTI, there may be chances your dog has bladder stones.

So if your dog is not responding to antibiotics, it's important to inform your vet. There are chances that your dog is suffering from something else that requires a different treatment plan. Sometimes, challenging cases require a referral to a specialist.

Antibiotic Not Being Absorbed

In some cases, the owners may be judiciously following the instructions, but the drug is not being properly absorbed. This can happen if the dog takes the antibiotic and then vomits shortly or has a condition that prevents the drug to be absorbed from the gastrointestinal tract.

In some cases, interactions with other medications are preventing the antibiotic from reaching sufficient bactericidal concentrations necessary to kill the bacteria. For instance, anti-acids have been known to interfere with and lower the absorption of certain types of antibiotics. Always let your vet know if your dog is on other supplements or medications when you are giving antibiotics so that you can be provided with guidelines on how to proceed.

 Drug Resistant Bugs

It's unfortunate, but the  incidence of multidrug-resistant organisms is on the rise and antibiotics not working may be indicative of this. How do these "super bugs" develop? As bacteria are exposed to more and more antibiotics, in order to survive, they develop a protective shell that prevents antibiotics from invading their cell walls. These super bugs then reproduce passing down this new mutation to the next generation. 

When these types of bugs are found, there is a limited line of drugs to resort to in order to combat these infections, and sometimes it is necessary to utilize human drugs such as vancomycin, carbapenems, and linezolid, explains veterinarian Dr. Jennifer L. Garcia, a board-certified veterinarian specializing in internal medicine. 

Veterinarians generally suspect drug resistant bugs based on the dog's symptoms, culture results and history of antibiotic drugs not working. Stronger drugs are used as a last resort after all other options have been exhausted and a specialist was consulted to determine whether there are other possibilities.

Final Thoughts

As seen, there may be various causes as to why your dog's antibiotics may not be working as expected. If your dog is on antibiotics and is not getting any better after a few days, consult with your vet. It's important that you inform your vet so that your vet can take other steps to help your dog recover.


  • DVM360, Hot Literature: Antibiotic guidelines for dogs and cats with urinary tract disease

[otw_is sidebar="otw-sidebar-1"]

Related Articles