Cephalexin antibiotics for dogs & side affects

Updated April 17, 2017

Dogs suffer from bacterial infections just like their human best friends. In some cases, medication approved by the FDA for human consumption only is more effective in treating the canine's infection. To aid veterinarians in their fight against animal disease, the FDA approved the Animal Medicinal Drug Use Clarification Act of 1994. This act allows veterinarians to prescribe human medication to animals under a classification known as "extra label" use. Cephalexin is one of these extra label drugs.


Mar Vista Animal Medical Center gives a historical accounting of cephalexin on their website. They explain that although penicillin truly was a wondrous discovery in the battle against bacterial infection, the medication falls short overall in total bacterial eradication in both humans and dogs; only 30 per cent of penicillin is absorbed by the body, and half of that is depleted within 30 minutes. Worse, certain strains of bacteria outsmart the drug, destroying it rather than the other way around. Needless to say, penicillin needed some improvement and cephalexin, a cephalosporin class antibiotic, was produced to do just that.


Mar Vista Vet further explains cephalosporin antibiotics are derived from bacterium (specifically, Cephalosporium acremonium) just like penicillin and are classified into three groups: first-, second- and third generation. Cephalexin is a first-generation cephalosporin, and provides effective treatment against the bacteria immune to penicillin, as well as anaerobic, or oxygen-intolerant, bacteria. In cases where a dog is infected with a penicillin-resistant bacterium, cephalexin's alternate genetic make-up provides effective relief.


Doctors Foster and Smith indicate that cephalexin is primarily prescribed for dogs to treat skin, urinary tract, bone and respiratory tract infections. Because cephalexin is considered safe for long-term use, it is particularly effective in treating deep skin infections, termed "pyodermas" by Mar Vista Vet, which might require antibiotic treatment for up to six to eight weeks.

Side Effects

All antibiotics come with side effects, and cephalexin is no different. reports dogs being administered cephalexin may experience vomiting and diarrhoea, allergic reactions (particularly if the canine is allergic to penicillin) signified by a rash, hives, shortness of breath and/or swelling of the face and mouth and, in severe cases of overdose, abdominal pain, muscle spasms, weakness and seizing. Added to these side effects may be hyperactivity and drooling, according to Doctors Foster and Smith.


Despite its effectiveness, Doctors Foster and Smith caution that cephalexin does not mix well with certain medications and supplements. They specifically call out "vitamins, supplements, aminoglycosides (gentamicin, neomycin) or amphotericin B, anticoagulants (blood thinners, such as heparin or warfarin), and probenicid" as no-nos in conjunction with cephalexin therapy. Additionally, if the dog is diabetic, cephalexin directly affects blood glucose test results with certain brands of urine test strips and might report false numbers.

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