Cephalexin for Dogs and Cats

Medically Reviewed by Joshua Conrad, PharmD on September 24, 2024
Written by Kathleen Claussen, DVM
5 min read

Cephalexin (Keflex, Rilexine) is a medicine used to treat dogs and cats for skin infections caused by certain bacteria, especially staph infections. It’s also used extra-label or off-label to treat them for other skin infections and urinary tract infections. Extra-label or off-label means a drug is used to treat something for which it’s not FDA-approved, but it’s safe and effective. Cephalexin can also be used extra-label in ferrets, reptiles, birds, and horses.

Cephalexin is a first-generation cephalosporin antibiotic. It’s good at killing most gram-positive bacteria, some gram-negative bacteria, and most anaerobic bacteria, which are bacteria that can live without oxygen. 

When cephalexin is a good choice for treating an infection, it’s best to use it first, saving more broad-spectrum antibiotics for harder-to-kill infections. This helps limit antibiotic resistance, which makes some bacteria harder to kill. That can lead to more serious or life-threatening infections.

Cephalexin is FDA-approved for treating skin infections caused by Staphylococcus pseudintermedius bacteria in dogs. It’s also used in the extra-label treatment of other bacterial infections (skin and urinary) in dogs and cats.

You can get it with a prescription from your vet, an online pharmacy, or human pharmacy. It comes as chewable tablets, tablets, capsules, and by-mouth liquid. Contact your veterinary compounding pharmacy for other dosing options.

It’s given to them by mouth as a chewable tablet, tablet, capsule, or liquid. It’s usually given twice a day for the length of their treatment. It’s important your pet takes all of their prescribed antibiotics, unless otherwise directed by your vet, even if they seem to be better. 

Cephalexin may be given with or without food. If your pet has an upset stomach after taking it with no food, try giving it to them with a small amount of food or a treat. The liquid medicine should be mixed well and correctly measured using the dosing dropper or syringe that comes with it. Give liquid meds in your pet’s mouth slowly, so they get the whole dose.

Always follow your vet’s directions for giving medicines to animals. Remember to tell them about any medicines, vitamins, supplements, or herbal therapies your pet gets. Talk to your vet before stopping any of your pet’s meds. 

Its benefits include:

  • It works against many different types of bacteria.
  • It starts to work in 2 hours.
  • Dogs and cats can usually take it without having side effects.
  • It comes in different forms, making it easy to find one your pet can take.

You and your vet should monitor your pet for improvement, as well as side effects of the medicine. Before starting them on cephalexin, your vet may do a test to make sure your pet is taking the best antibiotic for their condition. This is called a bacterial culture and sensitivity test. The results can take several days, and your vet may want your pet to start the medicine before the results are back. They might change your pet’s medicine when the results come in. Sometimes, the bacterial culture and sensitivity test may need to be repeated if your pet isn’t improving, or if their infection goes away and comes back.

Don’t use cephalexin if your pet is allergic to it or other medicines called cephalosporins. Use it with caution if your pet is allergic to penicillins. Also be cautious if your pet is breeding, pregnant, or nursing, as the safety of cephalexin hasn’t been studied in such animals. Also use cephalexin with caution if your pet is older or has kidney disease.

Side effects can happen. They’re usually related to your pet’s stomach and intestines, and may include:

  • Vomiting
  • Decreased or no appetite
  • Loose stool or diarrhea 

If your pet’s side effects are severe, get worse, or continue, stop giving them the medicine and contact your veterinarian. They’ll discuss treatment options with you, depending on your pet’s side effects. They may recommend switching to a different antibiotic. Your vet may recommend starting a probiotic to help change your pet’s gut flora, which are the good bacteria that live in their intestines.

While there’s a low risk of severe side effects, too much cephalexin can sometimes cause serious problems. These may include:

  • Tiredness 
  • Itching or scratching 
  • Drooling
  • Increased breathing rate 
  • Excitability
  • Fever
  • Kidney damage (rarely)

If you suspect your pet is having a serious side effect or they took too much of the drug, call your veterinary clinic right away. If it’s outside office hours, you may contact a local emergency veterinary hospital or an animal poison control center. You might have higher charges for emergency care.

You can reach the ASPCA Animal Poison Control Center at 888-426-4435 or the Pet Poison Helpline at 855-764-7661.

Giving your pet more than one medicine can sometimes change how those medicines work. It can also increase their risk of serious side effects. Tell your vet about any prescription or over-the-counter (OTC) medicines, vitamins/minerals, herbal products, and other supplements your pet takes.

Before starting cephalexin, tell your vet if your pet takes:

Omeprazole. This is a proton pump inhibitor (PPI) that reduces stomach acid production. It may decrease your pet’s ability to absorb cephalexin. A higher dose of cephalexin may need to be given if your pet also takes omeprazole. It’s not clear if this can happen with other PPIs or other medicines that reduce stomach acid, such as histamine-2 (H2) blockers (like famotidine) or antacids (like Maalox or Mylanta).

Warfarin. This is commonly used as a blood thinner to prevent blood clots in your pet’s bloodstream. There’s a greater risk of bleeding when this medicine is used with cephalexin.

Zinc. This is a nutritional mineral used to reduce copper toxicity in dogs, and treat some liver and skin issues in dogs and cats. Zinc can interfere with cephalexin when given at the same time, making cephalexin less effective. Give the cephalexin about 3 hours before the zinc.

Keep cephalexin out of the reach of children. Wash your hands after giving cephalexin to your dog or cat. Don’t handle cephalexin if you’re allergic to it.

The chewable form of cephalexin smells and tastes really good to a lot of dogs. Some may chew their way into the package if it’s left where they can get to it. These chewable tablets should be stored in their original prescription package or other tightly closed container. To prevent accidental taking, the package should be stored in a secure location out of the reach of your dog. If you think your pet took more cephalexin than prescribed, call your vet or vet emergency clinic right away.

If you realize you missed giving your pet a dose, go ahead and give that dose if it’s close to the original scheduled time. If it’s closer to the next dosing time, skip the missed dose completely and give your pet the next dose at the correct time. Don’t double the dose. 

Cephalexin chewable tablets, tablets, and capsules should be protected from moisture and light. Store them at room temperature. Store the liquid version in your fridge for up to 14 days before throwing away any unused amount.