Cephalexin is one of the most commonly prescribed antibiotics for dogs, used primarily to treat skin infections, urinary tract infections, and bone infections. It belongs to a class of drugs called first-generation cephalosporins, which work by breaking down bacterial cell walls. It’s especially effective against Staphylococcus bacteria, the species behind most canine skin infections.
Skin Infections
The single most common reason vets prescribe cephalexin for dogs is bacterial dermatitis, also called pyoderma. These infections show up as red, inflamed patches, pustules, or crusty sores on the skin and are almost always caused by Staphylococcus bacteria. Because cephalexin is particularly strong against Staph species, it’s considered a go-to choice for these cases. Superficial skin infections typically require treatment for at least three to four weeks, and deeper infections can require six weeks or longer. Your vet will likely want you to continue the medication for a period after symptoms clear to prevent the infection from bouncing back.
Urinary Tract Infections
Cephalexin is also effective for managing urinary tract infections in dogs. A standard course for a lower urinary tract infection runs about 10 days at a dose of 15 mg/kg given twice daily, though your vet may adjust this depending on severity. One important limitation: cephalexin is not expected to be effective against E. coli, which is actually a common cause of UTIs in dogs. It’s also ineffective against Pseudomonas bacteria. So if your dog’s UTI doesn’t respond to cephalexin, the vet may need to run a urine culture to identify the specific bacteria involved and switch to a different antibiotic.
Other Infections
Beyond skin and urinary tract infections, vets prescribe cephalexin for bone infections (osteomyelitis), wound infections, and respiratory infections when susceptible bacteria are involved. It’s also sometimes used as a preventive measure before or after surgery to reduce the risk of bacterial complications at the surgical site. In all of these cases, the drug works best against gram-positive bacteria, meaning it covers a narrower range of organisms than some broader-spectrum antibiotics.
Dosing and How to Give It
The standard dosing range for cephalexin in dogs is 15 to 45 mg/kg, given orally every 6 to 12 hours. That’s a wide range because the dose depends on the type and severity of infection being treated. The medication comes in capsules, tablets, and liquid suspension, all given by mouth.
You can give cephalexin with or without food. If your dog gets nauseous on an empty stomach, giving the pill with a small amount of food or wrapped in a treat usually solves the problem without affecting how well the drug is absorbed. The most important thing is to finish the entire prescribed course, even if your dog looks better partway through. Stopping early is one of the main reasons infections return or develop antibiotic resistance.
Side Effects to Watch For
Most dogs tolerate cephalexin well. The most common side effects are mild gastrointestinal issues: loss of appetite, vomiting, and diarrhea. These are usually manageable and often improve when the medication is given with food.
Less commonly, some dogs develop hyperexcitability and excessive drooling while taking cephalexin. If you notice either of these, let your vet know so they can switch to a different antibiotic. More serious allergic reactions are rare but possible. Signs include fever, skin rashes, difficulty breathing, and pale gums. These require immediate veterinary attention. Dogs with known allergies to penicillin-type antibiotics may be at higher risk for reacting to cephalexin, since the two drug classes share a similar chemical structure.
What Cephalexin Won’t Treat
Cephalexin is not a broad-spectrum antibiotic, so it has clear limitations. It won’t work against viral or fungal infections. It’s also ineffective against many gram-negative bacteria, including E. coli and Pseudomonas. If your dog has a mixed infection or one caused by resistant bacteria, your vet may need to use a different drug or combine antibiotics. This is why vets sometimes run a culture and sensitivity test before prescribing, particularly for infections that have already failed to respond to a first round of treatment.