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Why is my puppy's poop dark or constipated after Metronidazole?

Updated on September 23rd, 2025

Pet's info: Dog | French Bulldog | Male | unneutered | 2 months and 21 days old | 7 lbs

Can metrobactin make puppy poo very dark and constapated

4 Answers

Most Helpful Answer

Answered By Dr. Strydom, DVM

Veterinarian

Published on April 22nd, 2020

Not typically. Metronidazole does not have any listed side effects like that. Some common side effects are:

Nausea or vomiting.
Diarrhea.
Drooling.
Gagging or regurgitation.
Loss of appetite.
Lethargy or fatigue.
Blood or darkening of urine.
Fever.

So, If the stools are very dark brown that is not really a problem, but black, that is serious and you should call your vet. Black typically means there is bleeding somewhere in the GI tract.

If he is straining to defecate he may be constipated but straining can also be from diarrhea (if the stools are very soft/watery). I really don't have quite enough information to be helpful so I think it is probably best if you call your vet. If you want to do a one on one consultation with one our vets where we can chat back and forth then we may be able to help you better.

1Pet Parents found this answer helpful

Related Answers from Veterinarians

Answered By Stacey Anstaett, DVM
Veterinarian
Published on January 21st, 2019
It is not normal after they are dewormed to have watery, jelly bloody stools. Ideally, contact your veterinarian regarding the use of the metronidazole if you have some at home. Having said that, at a prescribed, recommended dose, metronidazole is often quite effective at getting the stool back under control. However, there could be additional things going on that need to be addressed. She is quite young; if she has any additional symptoms (inappetence or vomiting, lethargy, not playful) please take her to a veterinarian as soon as you can. She may have parvovirus, or another serious ailment.
Thank you for using Petco Pet Education Center, formerly Petcoach!
3Pet Parents found this answer helpful
Answered By Amber Da Silva, DVM
Veterinarian
Published on August 7th, 2017
If the Metronidazole was stopped before she got the full course, then it is possible she just didn't clear up completely. I've never seen Metronidazole cause constipation. Most of the time they don't have as many bowel movements because they haven't been eating their full amount and the intestines were empty from all of the diarrhea. I would continue the Metronidazole. if she still has diarrhea, with or without blood, or it comes right back after you finish the Metronidazole, this warrants another visit to the vet.
1Pet Parents found this answer helpful
Answered By Dr. Dayna, DVM, CVA
Veterinarian, Certified Veterinary Acupuncturist
Published on October 23rd, 2017
Metronidazole is a common therapy for bloody stool. As long as she is eating and feeling ok otherwise, then I probably wouldn’t have done lab work either. However, if she stops eating, starts vomiting, or not improving then a follow up visit with lab work and possibly x-rays would be appropriate. Best of luck and thank you for using Pet Coach.
3Pet Parents found this answer helpful

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