Cephalexin (Keflex®) is a 1st generation cephalosporin antibiotic sometimes prescribed for dogs. The drug works by intefering with the growth of susceptible pathogens and is most commonly used to treat Staph, but it is versatile and can treat many different infections of the urinary tract, respiratory tract, bones, joints, soft tissue and skin. It can also be used to prevent heart valve infections.

Despite its broad spectrum efficacy against both gram-positive and gram-negative bacterial infections, it is ineffective against most species of Enterobacter (a species of bacteria which can cause bacteremia, skin/eye infections and more).

Recommended Dosage

Note: Cephalexin is available by prescription only. Do not use it without the approval of your vet.

The dosage of cephalexin varies depending on which condition is being treated and may be adjusted in those with pre-existing medical conditions (such as kidney disease) to lower the risk of adverse effects. For the treatment of most infections, 13.6 mg/lb can be given by mouth twice a day.

A dosage of 13.6 mg/lb is shown on the chart below:

Keflex dosage chart
Dog’s Weight In Pounds: Dosage In Mg:

This medicine is also available as a liquid and an injection, but the use of tablets (especially the Rilexine® chewable tablets) is more common.


The concentration of liquid formulas can vary. Some formulations contain 125 mg of active ingredient per 5 milliliters while others contain 250 mg per 5 milliliters. As an example, if you were treating Staph with a dosage of 13.6 mg/lb you would need 0.54 mL of the 125 mg/5 mL solution or 0.27 mL of the 250 mg/5 mL solution for each pound your dog weighs.

How long should treatment last?

You should complete the full course of treatment recommended by your vet or continue giving the medicine for at least 3 days after your dog begins feeling better (with the vet’s approval). Ending treatment too soon could cause the infection to return.

Example Dosage: A 50 pound dog with ear infection could be given 500 milligrams every 12 hours (twice daily) for treating gram-positive infections.

Is It Safe?

It’s safe for most dogs to take this medicine but caution should be practiced when treating those with kidney disease. Those who have suffered negative reactions to cephalosporins or penicillin (including penicillin derivatives like Clavamox) in the past are more likely to react badly.

The possibility of affected motor function and reports of lameness are also important to consider.

Pregnancy: The safety of using this drug during pregnancy has not yet been established. For this reason, owners are advised to avoid giving it to a pregnant dog if possible.

Safety Guidelines

You will need to see a vet before using cephalexin. During the consult be sure to tell the vet about the following:

  • Other medication your dog is taking
  • Medical conditions your dog suffers with (particularly kidney conditions)
  • Any bad reactions your pet has had to penicillin or cephalosporins

If your dog experiences any adverse effects as a result of this drug call the vet to discuss the best way to proceed. If the reaction is severe it’s likely you will be asked to discontinue use of the medicine.

Contraindications/Drug Interactions: Dogs with diseases which affect kidney function, or those with a history of hypersensitivity to cephalosporin antibiotics may not be suitable for treatment (at least at the recommended dose). Using tablets is not recommended for treating animals with shock, blood poisoning or any serious illness – injecting the medicine is often better in these cases.

What Is It Used For?

Vets prescribe cephalexin to treat bacterial infections, especially Staph. It is not often used in cases of Enterobacter infection.

Side Effects

During treatment your pet may experience:

Most Common

  • Vomiting
  • Diarrhea
  • Weight loss


  • Salivation
  • Rapid breathing
  • Excitability
  • Kidney damage
  • Hypersensitivity reactions
  • Decreased motor control

It’s best to give the medicine with a small meal to help lower the chances of vomiting and diarrhea. Dogs who are allergic to this drug may experience adverse effects such as rashes, fever and anaphylaxis. You should always seek emergency veterinary care in the case of a severe allergic reaction or any other severe reactions.

Long-term use has been linked to neutropenia, granulopenia, decreased platelet count, hepatitis and kidney issues (for example tubular necrosis and interstitial nephritis).


Overdoses of cephalexin will not usually be harmful but could cause gastrointestinal problems (diarrhea and/or vomiting). Any dog who is sensitive to the drug could experience dangerous reactions following an overdose. If you suspect an overdose has been given (or has been accidentally ingested) call your vet or the ASPCA Animal Poison Control hotline immediately on (888) 426-4435.


Dr. D. Aucoin
Dr. K. Kwochka
Plumb’s Veterinary Drug Handbook (sixth edition)