Cephalexin for dogs is a broad-spectrum antibiotic belonging to the class of antimicrobials known as cephalosphorins. It is a first-generation cephalosphorin which has exceptional bactericidal effects against Gram-positive organisms and a number of Gram-negative organisms. It is not approved by the FDA for the management of bacterial infections in dogs caused by susceptible microorganisms. However, it is often prescribed and used by veterinarians as an extra-label antibiotic. It is for this reason that Cephalexin for dogs should be used with caution, under a vet’s guidance, and available only with prescription by a licensed veterinarian.


Being a broad-spectrum antibiotic, Cephalexin for dogs can be used in the management of the following infections.

  • Staphylococcal infections especially on the skin and at sites of skin irritation or wounds
  • Infections caused by Steptococcus pyogenes such as strep pharyngitis, cellulitis, and glomerulonephritis
  • Infections caused by Streptococcus pneumoniae including pneumonia, bronchitis, otitis media, meningitis, rhinitis, septic arthritis, sepsis, osteomyelitis, endocarditis, pericarditis, cellulitis, conjunctivitis, and brain abscess, among others
  • Infections caused by Haemophilus influenza such as pneumonia, cellulitis, infectious arthritis, osteomyelitis, epiglottitis, bacteremia, and bacterial meningitis
  • Infections caused by Proteus mirabilis like pneumonia and urinary tract infections
  • Infections caused by Klebsiella pneumoniae such as pneumonia, bronchitis, urinary tract infections, diarrhoea, cholecystitis, upper respiratory tract infections, bacteremia, and wound infections, and others
  • Infections caused by Escherichia coli like gastroenteritis where the main symptom is diarrhea

Technically, Cephalexin for dogs is prescribed in the management of ear infections, urinary tract infections, pneumonia, soft tissue and bone infections, and skin infections in dogs. While it is effective against Staphylococcus, it is largely ineffective against methicillin-resistant Staphylococcus aureus or MRSA.

It is also effective only against bacteria and not viruses, fungi, or other microorganisms.

In some cases, Cephalexin may also be given as a prophylactic antibiotic to help guard against infections in the dog’s heart valves caused by Streptococcus pyogenes. It can also be given in dogs that have wounds or even abscesses to prevent secondary bacterial infections.

Benefits of Cephalexin

There are a number of reasons why you may want to give Cephalexin to your pet. Here are some of the more common benefits of administering such a beta-lactam antibiotic.

  • Kills susceptible Gram-positive and Gram-negative bacteria
  • Provides an empirical treatment to ear, urinary tract, respiratory tract, bone, soft tissue, and skin infections
  • Protects the heart valves of the dog against possible bacterial infections
  • Prevents secondary bacterial infections in wounds

How Cephalexin Works

Cephalexin is considered a beta-lactam antibiotic belonging to the class of 1st generation cephalosphorins. Beta-lactam is one of the fundamental chemical structures in many antiobitics including the cephalosphorins, monobactams, carbapenems, and even penicillin. As such, these are collectively called as the beta-lactam antibiotics. Because of Cephalexin’s close chemical resemblance to penicillin and the other beta-lactam antibiotics, its mechanism of action follows the general mechanism of action of these chemicals.

Cephalexin exerts its bactericidal or bacteria-killing effect by inhibiting the formation or production of the peptidoglycan layer which is a very important component of the cell wall of bacteria. Without the peptidoglycan layer it would be impossible to maintain the integrity of the cell wall. More specifically, Cephalexin irreversibly binds to a very important active site for penicillin binding proteins or PBPs found in the bacterial cell wall. These PBPs are critical in the production of the cell wall of the bacteria. Cephalexin is able to bind with these specific sites because it closely resembles an amino acid – d-alanyl-d-alanine – which is important in the peptidoglycan layer. Instead of the amino acid binding to the PBPs, it’s Cephalexin that binds.

If the bacteria cannot synthesize its own cell walls it virtually leaves its internal cellular organelles exposed to immune systems cells like macrophages, phagocytes, neutrophils, and monocytes among other cells. When this happens, bacterial death ensues.

Among the different kinds of bacteria, Cephalexin has shown remarkable bactericidal activity against round-shaped Gram-positive cocci while showing moderate antibacterial activity against rod-shaped Gram-negative bacilli.

Unfortunately, some bacteria are able to produce an enzyme that effectively neutralizes or even destroys the beta-lactam ring of Cephalexin and other beta-lactam antibiotics. These bacteria produce beta-lactamase which can render the antibiotic largely ineffective. This is why there is now a growing number of bacterial species that are becoming more resistant to Cephalexin.

How Cephalexin Works

Potential Side Effects

It is important to understand that the veterinary use of Cephalexin is not really approved by the FDA. As such its administration should only be under the guidance of a vet to help minimize some of its potential side effects. The adverse reactions are mostly related to the death of susceptible bacterial species as they get cleared from the dog’s system. Additionally, since the structure of Cephalexin is somehow similar to an amino acid, there’s a possibility of initiating some reactions related to the activities of d-alanyl-d-alanine.

In general, however, Cephalexin for dogs is safe. Some of the more common side effects include nausea and vomiting as well as the passage of loose, watery stool or diarrhea. In some cases, weight loss, drooling, and panting have been observed.

If your dog is sensitive to penicillin there is a great chance that it will also be sensitive to Cephalexin as they both belong to the same class of antibiotics. As such skin rashes, hives, and difficulty breathing or rapid yet shallow breathing may occur as a result of an allergic reaction. Swelling of the dog’s mouth, tongue, or throat can also occur. In such cases, it is imperative that the dog be brought to a veterinary clinic immediately especially if a life-threatening anaphylactic reaction occurs.

In very rare instances, decreased motor control, kidney damage, granulopenia, neutropenia, and decreased platelet count can occur especially in chronic use of the beta-lactam antibiotic.

Things You Should Know about Cephalexin

Cephalexin is a broad-spectrum antibiotic that is often indicated as an extra-label management of infections in dogs caused by susceptible Gram-positive and Gram-negative bacteria. It is not approved by the FDA for veterinary purposes and as such should always be given to dogs with extreme caution. It is a relatively safe antibiotic that is considered by many vets as a good alternative to penicillin.

What You Should Tell Your Vet before He Prescribes Cephalexin

Your vet should know if your dog has been diagnosed with a kidney problem in the past. Also any history of adverse reactions to other cephalosphorins or penicillin or any other medication at all should also be divulged. Additionally, if your pet is currently taking any medications, supplements, or any other substance you should also tell your vet about these. Nursing and pregnant dogs are not absolute contraindications to the use of Cephalexin. However, your vet still deserves to know if your pet is pregnant or nursing.

How to Give Cephalexin to Your Dog

Cephalexin is available in different formulations, although the oral tablet or pill formulation is a lot easier to administer for pet parents. The dosage recommendation stands at 10 to 15 milligrams for every pound of the dog’s body weight. The total dose can be divided in two to 3 doses per day or every 12 or 8 hours, respectively. You can give Cephalexin to your dog together with its meal or without, although giving it with food can help reduce the gastrointestinal side effects especially diarrhea.

The antibiotic treatment usually lasts about 7 to 10 days, often depending on the type of infection and the dog’s response to the antibiotic therapy. In cases where after 5 days and there are no noticeable improvements in the dog’s condition, a clinical reevaluation will have to be performed and determine if the initial diagnosis persists or has already been replaced with another disease entity. If it’s the latter, then the immediate identification of the cause is warranted so appropriate treatment can be initiated.

What to Do If You Miss a Dose

In case you forgot to give your dog its Cephalexin, you should give it the moment you remember it. However, don’t give the dose if it’s already almost time for its next scheduled dose.

What to Do in Case of Cephalexin Overdose

Overdose is not really an issue with Cephalexin except that excessive administration of the antibiotic can lead to vomiting, diarrhea, and other gastrointestinal complaints. If your pet also happens to be hypersensitive to Cephalexin, there’s a chance that an anaphylactic reaction may occur. This requires emergency veterinary consult.

Some Drug Interactions

Cephalexin may have the potential to interact with other types of antibiotics, loop diuretics, probenecid, or warfarin. If these medications are currently being given to your dog your vet may have to adjust the dose if not complete replace it with another agent. Other medications and supplements may potentially interact with Cephalexin so the vet should be duly informed.

Cephalexin for dogs is an effective antibiotic for canine infections caused by susceptible Gram-positive and Gram-negative bacteria. It is a safe antibiotic with gastrointestinal complaints being the principal side effects. However, it’s not really approved by the FDA for vet use so its use should be under the guidance of a vet.


Olivia Williams
Olivia is our head of content for MyPetNeedsThat.com, mum of one and a true animal lover. With 12 different types of animal in her family, it's never a dull moment. When she isn't walking the dogs, feeding the cats or playing with her pet Parrot Charlie, you will find her product researching and keeping the site freshly updated with the latest products for your pets!


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