By Rania Gollakner, BS, DVM, MPH

person's hand holding a tablet for their dog

What is cephalexin?

Cephalexin (brand names Rilexine®, Keflex®, Vetolexin®) is an oral antibiotic that is used to treat pyoderma and other bacterial skin infections in dogs and is used off-label or extra-label in cats, horses, ferrets, reptiles, and birds to treat pyoderma and some other types of skin infections. It is sometimes used off-label or extra-label to treat some urinary tract infections in cats and dogs. Many drugs are commonly prescribed for off-label use in veterinary medicine. In these instances, follow your veterinarian’s directions and cautions very carefully.

How is cephalexin given?

Cephalexin is available as a capsule, chewable tablet (for dogs), and oral suspension (liquid). In Canada, it is also available in an oral paste. Cephalexin can be given with or without food. If your pet vomits or seems unwell after receiving the medication, try giving it with a small amount of food. Shake the liquid form well and measure doses carefully.

This medication will start working in one to two hours, but visible effects may take a few days to be recognized. It is very important that your pet completes the antibiotic as directed by your veterinarian even if your pet seems to be feeling better.

What if I miss giving my pet the medication?

If you miss a dose, give it when you remember, but if it is close to the time for the next dose, skip the dose you missed and give it at the next scheduled time. Never give your pet two doses at once or give extra doses.

Are there any potential side effects?

Side effects to cephalexin are usually mild and rarely occur. It may cause gastrointestinal upset including lack of appetite, vomiting, and diarrhea. If these side effects become severe, contact your veterinarian. More severe complications can occur if your cat stops eating, so contact your veterinarian if your cat has not eaten for 24 hours. Fever, rashes, difficulty breathing, and/or pale gums are side effects that may indicate an allergic reaction to the drug. Very rarely, cephalexin may cause serious skin reactions. Contact your veterinarian immediately in these cases. This short-acting medication should stop working within 24 hours, although effects can be longer in pets with liver or kidney disease.

Are there any risk factors for this medication?

Do not use cephalexin in pets that have a known hypersensitivity or allergy to cephalosporins. It should be used with caution in pets that are sensitive to certain other antibiotics including penicillins, rapamycin, and carbapenems. Use cautiously in pets with kidney dysfunction; lower doses may be necessary. Cephalexin should be used with caution in pregnant and nursing mothers. Use cautiously in rabbits and small rodents.

Are there any drug interactions I should be aware of?

Certain drugs may interact with cephalexin including probenecid (Benemid®, Benuryl®) and Warfarin (Coumadin®, Jantoven®, Panwarfin®). There are no known drug interactions with cephalexin in animals; however, be sure to tell your veterinarian about any medications (including vitamins, supplements, or herbal therapies) that your pet is taking.

Is there any monitoring required with this medication?

Pets with kidney disease may require monitoring. Monitor for efficacy and for side effects.

How do I store cephalexin?

Cephalexin should be stored in a tightly sealed container, protected from light, and at room temperature (between 15° and 30°C or 59° and 86°F). Oral suspensions should be stored in the refrigerator and disposed of after 14 days.

What should I do in case of an emergency?

A large overdose can cause serious complications. Call your veterinary office immediately if you suspect an overdose or an adverse reaction to the medication. If they are not available, follow their directions in contacting an emergency facility.

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