My dog had roundworms, but tested negative after treatment. Why?

No, it's not necessary for a dog to vomit or have diarrhea after being dewormed. It's a side effect but it doesn't happen to all dogs. A lot of times, the only sign of worms in dogs is eggs in the poop, which are microscopic. It will still be working even if you don't see worms in Ember's poop.

What you are seeing are likely dead or dying intestinal parasites. It is common to see parasites in the stool after deworming. You may need to repeat the deworming in 2-3 weeks to kill any remaining parasites that were not developed at the time or the first deworming.

If your dog is sick three hours after giving the worming treatment, this should be sufficient time for the worming treatment to be absorbed. To err on the side of caution, if your dog is known to be infested with worms, it might be a good idea to re-treat him in a week's time with a different product. I'm not sure which product you are currently using, but I recommend using Drontal. You can get a Drontal tablet from your vet. If that doesn't make him sick, you can use it as your regular worming treatment.

It is not typical to have side effects a week after being treated for tapeworms so there could be something else going on. If he hasn't had a stool sample tested for parasites then you should take a sample to your vet for testing. He could have additional parasites and need a different dewormer. Continue to monitor him and if his signs continue or progress then he should be examined by a vet to determine the cause and treat. Dogs get tapeworms from eating fleas so he should be treated for fleas with a medication, like NexGard, Frontline, Bravect, etc. Hope he feels all better soon!

Hello. Most wormers will begin working the moment they hit the gut, so generally pretty quickly. Depending if Gunner's symptoms were due to the roundworms, he should be doing better within a day or so. Thanks for using Petco Pet Education Center, formerly Petcoach.

Hi, thanks for using Petco Pet Education Center, formerly Petcoach! Hopefully seeing the worms pass in her stool means that the medications are working. I recommend rechecking a stool sample in 3-4 weeks to make sure there are no eggs present

If it is just intestinal parasites, several dewormings should be enough to set Nacho on the path to recovery. It may take a week or two unless he has an exceedingly high worm burden. If he isn't showing improvement a few days after being dewormed, have him rechecked by your veterinarian. Supportive care may be indicated until he is feeling better.