List of 5 Common Antibiotics for Dogs: Uses and Side Effects

Updated June 15, 2022
selective focus of a dog and a hand with a thyroid pill for a springer spaniel.

Dogs commonly take antibiotics to treat bacterial infections, and many of the antibiotics prescribed for dogs are the same types that are given to people. However, the doses used for dogs can be different. Antibiotics vary in their chemical structure, and this determines what type of infections they treat and whether they kill the bacteria (bactericidal) or simply slow bacterial growth to let the immune system defeat the infection (bacteriostatic). Some antibiotics can be given as pills or oral liquids, while others require an injection.

Can Dogs Take Penicillin?

According to the American Chemical Society, penicillin was discovered by Alexander Fleming on September 3, 1928. It was the first antibiotic and became a life-saving drug for treating infections in people. Penicillins damage the cell wall of bacteria and can also interfere with enzymes important to cell wall synthesis. Several antibiotics for dogs are in the penicillin class:

  • Amoxicillin
  • Amoxicillin-clavulanate (Clavamox)
  • Penicillin G
  • Ampicillin
  • Ampicillin-sulbactam (Unasyn)


Penicillin can be used to treat urinary tract infections, skin infections or wounds, and upper respiratory infections, or as part of a combination protocol for liver and biliary disease, serious systemic infections, or sepsis in dogs. Penicillins are effective against Streptococcus spp., Staphylococcus spp. (not all penicillins), Pasteurella spp., and some anaerobic bacteria.

Penicillins are not effective against Mycoplasma spp. infections and may not work well for infections of the prostate, eye, testicles, or lungs. In many infections, penicillins may be one of the first antibiotics used for treatment before further testing is done or a culture is taken.


Dogs can take penicillins. However, any antibiotic can affect normal gastrointestinal flora, and treatment may result in vomiting, diarrhea, or poor appetite. Occasionally, dogs have allergic reactions to these antibiotics. Penicillins are generally safe, but at excessively high doses, neurotoxicity or elevation in liver enzymes may be seen.

Fluoroquinolones for Dogs

Fluoroquinolones are a class of antibiotics that are used in both dogs and people. They are bactericidal antibiotics that inhibit bacterial growth by targeting enzymes vital to DNA replication. Fluoroquinolones are available in oral and injectable forms, and different types are available specifically for dogs compared to those used in people. Common fluoroquinolone antibiotics used in dogs include:

  • Enrofloxacin (Baytril)
  • Orbifloxacin (Orbax)
  • Marbofloxacin (Zeniquin)
  • Ciprofloxacin


Fluoroquinolones are used to treat many gram-negative bacterial infections, including those with Escherichia coli, Klebsiella, or Pseudomonas. Infections of the respiratory tract, intestines, urinary tract, and skin are often susceptible. Fluoroquinolones can reach particular parts of the body that other antibiotics may not, and are recommended for infections of the prostate, central nervous system, and bones and joints.

In general, this class of drug is not effective against Staphylococcus spp., Streptococcus spp., Brucella spp., Mycoplasma spp., Mycobacteria spp., or anaerobic bacteria. Additionally, many species of bacteria that are usually susceptible to these antibiotics are developing resistance, so a culture is often recommended before using a fluoroquinolone.


While it may be tempting to ask your veterinarian for a prescription for the less expensive drug ciprofloxacin, instead of the veterinary-specific fluoroquinolones, this is not ideal. Although ciprofloxacin may work for some pets, it is not reliably absorbed well in dogs.

These antibiotics can disrupt the normal flora of the gastrointestinal tract and their use in treating canines may lead to vomiting, diarrhea, or poor appetite. Other side effects of fluoroquinolones include damage to the joints of growing dogs when used at high doses, allergic reaction, and rarely, elevated liver enzymes, nervousness, and neurologic symptoms. When using a fluoroquinolone antibiotic, making adjustments to dosages of other drugs being administered is sometimes necessary.

Pet animal's skin

Tetracyclines for Dogs

Of the tetracycline class of antibiotics, doxycycline is one of the most commonly used in dogs. It is available in a generic formulation, and comes in tablets, liquid, and injectable forms. Tetracycline antibiotics have been in use since the 1940s and work by interfering with protein synthesis of microorganisms.


Veterinary experts agree that doxycycline is the antibiotic of choice for use in dogs with tick-borne diseases, such as Lyme disease, ehrlichiosis, or anaplasmosis. It is often used as part of a protocol in the treatment of heartworm disease, in which it targets the bacteria Wolbachia spp., an infection of the heartworms themselves that may contribute to inflammation in a dog's airways.

Doxycycline can be used to treat respiratory infections, such as kennel cough. It is also effective against leptospirosis, Bartonella spp., and some staph infections. Minocycline is another tetracycline antibiotic that is used on occasion.

Bacterial resistance to tetracyclines, including doxycycline, is common, and this antibiotic class is not usually effective against bacterial infections of Pseudomonas spp., Proteus spp., Serratia spp., Klebsiella spp., and many strains of E. coli.


Potential side effects of doxycycline in dogs include vomiting, diarrhea, loss of appetite, elevation of liver enzymes, nd allergic reaction. Doxycycline should not be given with foods that contain calcium, such as dairy products. If you need to hide your dog's pill in food for administration, avoid using cheese or cream cheese with this medication and elect for another type of treat instead. This antibiotic is not recommended for use during a dog's pregnancy, as congenital defects or dental or bone staining can result.

Cephalosporins for Dogs

First discovered in 1945, the cephalosporin class of antibiotics is divided into different subclasses. First- through fifth-generation cephalosporins are used in human medicine, while first- through third-generation drugs are used in dogs. Cephalosporins are bactericidal and work in a similar fashion to penicillins by attacking bacterial cell walls. Some cephalosporins available for dogs include:

  • Cephalexin (Keflex, Rilexine)
  • Cefadroxil (Cefa-Tabs, Cefa-Drops)
  • Cefazolin - a common injectable cephalosporin
  • Ceftiofur (Naxcel)
  • Cefpodoxime (Simplicef)
  • Cefovicin (Convenia), a long-acting injectable antibiotic for dogs and cats


First-generation cephalosporins are useful in treating gram-positive bacterial infections and a few gram-negative bacterial infections, including those with E. coli, Proteus, Klebsiella, Salmonella, and Enterobacter. Cephalexin and cefpodoxime are most often used to treat skin infections (Staphylococcus pseudintermedius) and urinary tract infections, but are not as useful against anaerobic bacteria as are penicillins.

Second- and third-generation cephalosporins have a broader spectrum of activity with less bacterial resistance. These can be used during surgery and are effective against a variety of gram-positive and gram-negative organisms, depending on the specific drug.


As with other antibiotic classes, these medications can potentially lead to gastrointestinal upset, including vomiting, diarrhea, or poor appetite. Other side effects of cephalosporins include allergic reaction, increased salivation, hyperexcitability, and with high doses, or rarely, kidney toxicity, severe skin reactions, neurologic symptoms, or blood cell changes. It's important to speak to your veterinarian right away if you notice any adverse effects.

Nitroimidazoles for Dogs

While many antibiotics can cause diarrhea as a common side effect, metronidazole -- also known by the brand name Flagyl -- is one of the medications most commonly used to treat diarrhea in dogs. It is a member of the nitroimidazole class of antibiotics and is the only drug in this group that is typically used in dogs. The mechanism by which metronidazole works to kill bacteria and other susceptible organisms is not completely understood, but it does attack the DNA of the infecting agents. This antibiotic is available in oral or injectable forms.


Metronidazole is used to treat anaerobic bacteria infections and certain protozoal parasite infections, such as Giardia. Susceptible bacteria may include Bacteroides fragilis, Fusobacterium spp., and Clostridium spp. Metronidazole is also used for the treatment of inflammatory bowel disease, oral and dental infections, pancreatic insufficiency, or other infections causing diarrhea.


Side effects of metronidazole can include vomiting, diarrhea, loss of appetite, lethargy, weakness, low blood counts, liver toxicity, or blood in the urine. Rarely, severe skin reactions can occur. When metronidazole is used at moderate to high doses over a long period, your dog may develop neurologic symptoms, including ataxia (wobbliness), difficulty walking, or abnormal eye movements. Fortunately, these symptoms will stop once the medication is out of your dog's system. Metronidazole is not recommended for use in pregnant dogs.

Routes of Antibiotic Administration

Most commonly, antibiotics are administered orally to dogs. However, this is not always the case. Mild infections may be treated locally, and even systemic infections can be treated through multiple routes. The most common routes of administration for dog antibiotics include:

  • Orally: by mouth; Generally, these are systemic antibiotics for infections of the intestines, urinary tract, respiratory tract, gingiva, skin, etc.
  • Topically: on the skin; For mild skin infections, your veterinarian may prescribe an antibiotic ointment, such as Animax, for you to apply to your dog's dermal layer. Mild ear infections are often treated with topical antibiotic products.
  • Ocularly: in the eye; Antibiotic eye drops, including tobramycin and ofloxacin, are prescribed for dog eye infections.
  • Subcutaneously: under the skin; It's possible an antibiotic injection may work to treat your dog's infection. Various antibiotic classes are available in this form. However, most are short-acting, with the exception of Convenia, a common long-acting injectable antibiotic for dogs.
  • Intravenously: within the vein; For severe infections, such as sepsis, Salmonella infection, etc., your veterinarian may recommend hospitalization with intravenous antibiotics.

Long-acting Injectable Antibiotic for Dogs

Close up of vaccinating an animal at vet's office

Cefovecin, an injectable cephalosporin most well-known by the brand name Convenia, has become a commonly used antibiotic in veterinary medicine. As the brand name implies, this drug is highly convenient. A single injection under your dog's skin will work for up to 14 days.

This long-acting injectable antibiotic may be a good option for dogs who are difficult to medicate, or for owners who may not feel comfortable administering antibiotics to their dogs at home. However, it is not effective for all types of infections. In general, it is used to treat wounds, skin infections, periodontal disease, abscesses, urinary tract infections, and soft tissue infections.

Due to its long-lasting abilities, this drug will remain in your dog's system for as long as 65 days. Adverse side effects, including lethargy, vomiting, diarrhea, and reaction at the injection site, may persist for up to 65 days, though most pets tolerate it well. Cefovecin is dosed based on your dog's weight. The medication is rather pricy, and an injection for a large dog can easily cost over $100. For this reason, it is most frequently used in cats and smaller dogs.

How to Give Antibiotics to a Dog

Oral antibiotics should generally be given with food. Fortunately, one of the easiest ways to give your dog an antibiotic pill or capsule is to hide it in a piece of dog-safe food. Commercial treat pouches are also available that can easily conceal a pill. These are a great option for dogs with food allergies, as hypoallergenic varieties are available.

However, if you're having difficulty with this method, you can ask the prescribing veterinarian if you can crush the pills or open up a capsule to better hide the taste of the pill. Certain formulations of dog antibiotics may be flavored and chewable, so dogs will simply take them like a treat.

Some antibiotics can be dispensed in a liquid form (usually for smaller dogs) and must be squirted into the mouth using a dropper or syringe. It may be tempting to mix these medications into your dog's water bowl, but this isn't recommended, as the entire dose needs to be given at one time.

If you feel administering a liquid would be less stressful for you or your dog, ask your veterinarian if the prescribed antibiotic comes in a liquid suspension. Even if it's not commercially available in this form, it's possible to have most medications compounded into a liquid through a compounding pharmacy. However, this may significantly increase the price of the medication.

Administer Antibiotics as Directed

Make sure that you finish giving all the antibiotics prescribed for your dog, and see your veterinarian for a recheck if that was recommended. The vet may need to assess your dog to decide if a longer course of antibiotics is necessary to clear the infection. If you think that your pet is having side effects from antibiotic treatment, contact your vet to discuss whether a change in medication is necessary.

Can a Pet Owner Give Antibiotics?

You may already have antibiotics at home from when your dog or other pet was sick. However, it is not a good idea to give these to your dog without first seeing your veterinarian. These are prescription medications, so they should not be administered without seeking medical advice.

While dogs can take many of the same antibiotics that are prescribed for people, they cannot always tolerate these medications, and the doses may be different from what an adult person would need. Different types of infections may also require a specific antibiotic class, so it's important to have your veterinarian advise you on the best way to treat your pet.

See Your Veterinarian

It is also best to avoid giving your dog antibiotics before seeing your veterinarian, because these medications can affect test results that will be important for your vet to reach a diagnosis. If the antibiotic starts to work before your pet can be checked over, the veterinarian may not be able to tell where the infection is located or how severe the infection is. In cases of a severe infection, a sample of the infected tissue or discharge is usually collected. If a pet has received antibiotics before this sample is taken, the results may not be accurate.

Concerns With Overuse

A final concern with antibiotic treatment is that these drugs are often overused, and this can contribute to the development of bacterial resistance. When antibiotics are used inappropriately -- for example, if they are used for the wrong type of infection, at an inadequate dose, or for an insufficient time period -- hardy bacteria can still survive and will then pass their survival traits on to other bacteria.

These resilient bacteria will grow and produce a more serious infection that can no longer be cured with common or inexpensive antibiotics. The Centers for Disease Control outlines many of the dangers of bacterial resistance on their web page.

Best Antibiotics For Dogs

Many dogs will need to take antibiotics at some point in their lives. With a thorough course of the appropriate antibiotic, your canine companion will be feeling back to normal in no time at all. When your dog is sick, it's natural to want to give them something to make them feel better. However, it's critical to resist treating your dog without first speaking with your veterinarian. In the case that your dog does need antibiotics, this type of drug can be used to treat several common medical problems in dogs, and many classes and routes of administration are available.

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List of 5 Common Antibiotics for Dogs: Uses and Side Effects