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My dog is vomiting, lethargic after cephalexin. Allergic reaction?

Updated on September 23rd, 2025

Pet's info: Dog | German Shorthaired Pointer | Female | spayed | 80 lbs

I have my 80 lb, 12 yr old dog her first dose of cephalexin 500mg. She's lethargic, had diarrhea, vomited, and will not eat. Could she be allergic?

2 Answers

Most Helpful Answer

Answered By Dr. Melanie, BVSc MS

Veterinarian

Published on October 15th, 2018

Usually cephalexin is well tolerated by dogs, but it can cause nausea, vomiting, and diarrhea. This can be alleviated by giving Molly her medication with food, but to be safe, I'd give your vet a call to let them know she is having these side effects. They made decide to have you stop giving it, and may want to try a different medication. I'd give your vet a call now. Best of luck.

1Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Dr. Leigh, DVM
Veterinarian
Published on November 18th, 2016
That is not a typical side effect of either medication. Cephalexin is an antibiotic which is usually well tolerated but may cause some gastric upset and endosorb is used to treat diarrhea. I am not sure of the clinical signs that your dog was having but if he is having diarrhea and seems lethargic than you should call your vet and give him/her an update, especially if he isn't eating and/or vomiting. Your vet may want to see your dog again. He could have an infection or a parasite and your vet can do some lab-work to help diagnose. Hope he feels better soon!
1Pet Parents found this answer helpful

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