Cephalexin (Keflex®, Rilexine®) for Dogs and Cats

Cephalexin (Keflex®, Rilexine®) for Dogs and Cats

cephalexin for dogs and catscephalexin for dogs and cats
cephalexin for dogs and catscephalexin for dogs and cats

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Overview of Cephalexin for Canines and Felines

  • Cephalexin, also known by the brand names Keflex®, Keftab®, Biocef®, and Rilexine®, is an antibiotic used for dogs and cats. Cephalexin belongs to the cephalosporin class of drugs and is related to the penicillin drugs in how it kills bacteria. Cephalosporins have a much broader range of activity against bacteria than penicillin.
  • Cephalexin is a first-generation cephalosporin that works by preventing bacteria from forming an adequate and protective cell wall. This results in instability and subsequent death of the bacteria.
  • When taken orally, cephalexin is readily absorbed with peak serum levels developing within two hours.
  • An antibiotic does not kill all types of bacteria, but rather has a spectrum of focus. Cephalexin works against gram negative and anaerobic organisms including the common Escherichia, Klebsiella, Proteus mirabilis, Pasteurella multocida, and the common Streptococci and most Staphylococci. It is generally not effective against Aerobacter, Bacteroides, Enterococcus, Mycoplasma spp., methicillin-resistant staphylococci, Pseudomonas, some Proteus bacteria, Rickettsia spp., fungi, and viruses.
  • Cephalexin is a prescription drug and can only be obtained from a veterinarian or by prescription from a veterinarian.

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Brand Names and Other Names of Cephalexin

  • There are various formulations and alternative names, such as Cefalexin, Cephalexin monohydrate, and Cephalexin monohydrochloride.
  • Human formulations: Keflex® (Dista), Cephaforte® (Jurox), Celexin, Cepexin, Cephacillin, Ceporexin, Ilium® (Troy), and various other generic forms.
  • Veterinary formulations: Rilexine® (Virbac), Ceporex® (Intervet), Cephacare® (Animalcare LTD), Cefaseptin® (Vetoquinol), Cephorum® (Forum Animal Health), Ceporex® (Intervet), Cefabactin® (Le Vet Beheer), Petalexin® (Alfamed), Therios® (Ceva), and various other generic forms.

Uses of Cephalexin for Dogs and Cats

  • Cephalexin is used in both dogs and cats to treat a variety of bacterial infections, including skin infections (pyoderma), wound infections, bone infections (osteomyelitis), pneumonia, upper respiratory tract infections, mastitis, and urinary tract (bladder) infections.
  • Cephalexin is similar to the veterinary drug cefadroxil, and veterinarians often use the two drugs interchangeably. The drugs have equal effectiveness.
  • Cephalexin is not effective against infections caused by parasites (intestinal worms), mites, viruses, or fungi.

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Precautions and Side Effects

  • While generally safe and effective when prescribed by a veterinarian, cephalexin can cause side effects in some animals. Cephalexin should not be used in animals with known hypersensitivity or allergy to the drug. If a dog or cat is already sensitive to allergy or vomiting from other cephalosporin drugs (cefadroxil) or penicillin (amoxicillin, ampicillin), cross-reaction with cephalexin is possible. Signs of an allergic reaction include rash, hives, scratching, facial swelling, or irregular breathing. If you suspect your pet is having an allergic reaction, please contact your veterinarian immediately.
  • The most common side effect in dogs and cats is vomiting shortly after administration. It is usually not a sign of serious disease, but indicates that the pet is sensitive to this drug. It is also not unusual for some animals to develop diarrhea from orally administered antibiotics like cephalexin. However, this has not been a common complaint with cephalexin. Other possible side effects include a decreased appetite, drooling, lethargy, or increased activity or excitement. Some cats can develop a fever.
  • High doses and overdoses have led to blood abnormalities, including low white blood cell counts (neutropenia).
  • Cephalexin should be used with caution in pets with a history of seizures or epilepsy, who are pregnant, or in pets with kidney (renal) failure. Cephalexin appears to be safe in pets that are lactating. A lower dose is recommended for pets with kidney failure.
  • Humans with a history of allergies to cephalexin or penicillin drugs can be sensitized by touching the drug. In these cases, gloves should be used when handling the medication or someone else in the home should administer cephalexin to your pet.
  • Keep out of the reach of children or curious pets who may accidently overdose. Minimal treatment is generally required for mild overdoses, but gastrointestinal decontamination and intravenous (IV) fluids may be required for large overdoses. Contact your vet immediately if you suspect your pet has ingested enough cephalexin to overdose.
Key Points About Giving Cephalexin to Your Pet

  • Cephalexin is an antibiotic used in dogs and cats to treat various respiratory, urinary, and skin infections.
  • Cephalexin is commonly prescribed due to its effectiveness, low occurrence of side effects, and minimal cost.
  • Cephalexin is not available over the counter. It is a prescription drug. A prescription can be obtained from your veterinarian and filled at veterinary hospitals or most human pharmacies.
  • Cephalexin may be used in combination with other antibiotics to combat a larger spectrum of bacteria.
  • It is normal for cephalexin to have a sulfur-like smell (somewhat similar to cat urine).
  • The dosage, duration, and frequency of treatment varies depending upon the underlying condition, response to the medication, and the development of adverse effects.
  • The most common side effects are nausea and vomiting. If this occurs, cephalexin should be given with food or a treat.
  • You should see therapeutic benefit within 24 to 48 of initiating therapy. If you do not see an improvement in your pet’s clinical signs, please contact your veterinarian.

Drug and Laboratory Test Interactions

  • Cephalexin has minimal interactions with other medications and is often given concurrently with many cardiac, respiratory, and thyroid medications.
  • However, it is possible for cephalexin to interact. Drugs that interact include certain other antibiotics like aminoglycosides (Gentamycin), amphotericin B, chloramphenicol, cholestyramine, estrogens, furosemide, metformin, metoclopramide, omeprazole, pantoprazole, probenecid, and warfarin. Consult with your veterinarian to determine if other drugs your pet is receiving could interact with cephalexin.
  • It is possible for administration of cephalexin to cause false results on laboratory tests including glucose, albumin, Coombs, and urine protein.

How Cephalexin Is Supplied and Stored

  • Cephalexin is most commonly available in 250 mg and 500 mg capsules and 50 mg, 75 mg, 150 mg, 200 mg, 250 mg, 300 mg, 500 mg, 600 mg, 750 mg, and 1000 mg tablets.
  • It is also available as a chewable scored tablets (Rilexine®) in sizes of 75 mg, 150 mg, 300 mg, and 600 mg (liver-chicken flavor).
  • Oral suspension is available in strengths of 25 mg/ml, 50 mg/ml, 100 mg/mL, and 150 mg/mL. Most manufacturers indicate the oral suspension is stable for 14 days following reconstitution.
  • An oral paste is available in the concentration of 100 mg/mL.
  • Tablets, capsules, and oral formulations should be stored at room temperature (65 degrees Fahrenheit to 77 degrees Fahrenheit).
  • An injectable version in the concentration of 150 mg/mL and 180 mg/mL is available in some countries.

Dosing Information of Cephalexin for Dogs and Cats

  • Cephalexin is a prescription drug and available only through a prescription by a licensed veterinarian. It is not available over-the-counter. Medication should never be administered without first consulting your veterinarian.
  • The dosage and frequency recommended for cephalexin will depend on the underlying condition being treated. The dose of cephalexin for dogs and cats ranges from 10 to 18 mg per pound (22 to 40 mg/kg) every 6 to 12 hours orally for 7 to 28 days. Treatment may extend for a week beyond resolution of signs or a negative culture test. Some chronic conditions, such as pyoderma, may require a prolonged maintenance therapy that can extend for a year.
  • The most common dose recommended is 10 to 15 mg per pound twice daily. This means that a 10-pound dog or cat would receive approximately 100 to 150 mg total per dose and a 40-pound dog would receive 400 to 600 mg per dose.
  • Reduced dosages are recommended for pets with kidney failure.
  • Medication should be given at the same time each day. Do not skip doses or stop the medication unless directed by your veterinarian. If you miss a dose and remember it within 4 hours, give it immediately then give the next scheduled dose as per the original schedule. If it has been longer than 4 hours since you missed a dose, give the next scheduled dose. Do not give a double dose unless otherwise instructed by your veterinarian.
  • Cephalexin should be administered with food or a treat if it causes nausea or vomiting in your pet.
  • The duration of administration depends on the condition being treated, response to the medication, and the development of any adverse effects. Be certain to complete the prescription unless specifically directed by your veterinarian. Even if your pet feels better, the entire treatment plan should be completed to prevent relapse or the development of resistance.


  • Plumb DC: Cephalexin. In Veterinary Drug Handbook. Ames, IA, 9th edition, Iowa State Press, 2018.
  • Physician’s Desk Reference. 56th Montvale, NJ, Medical Economics Company, Inc. 2000.
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