How long will it take before I stop seing worms in my dogs stool?

My dog is due for his third dose of Pyrantel tomorrow. he is still passing worms is this normal. I have my other dogs on pills containing Ivermectin to prevent them from infection.

He's passing the worms to get them out of his system which is a good thing if he's taken the deworming, it may happen for a couple of days, but not too long, wait a while, and if you are getting more concerned, then call the vet for advice, he'll know best.

You have to give the medicine time to run its course so after the last dose it will be least 1 or 2 days before they are all gone

yes, this means the medication IS working. it's very good your other dogsare on ivermectinmake sure you talk to your vet about reworming him in 10 days or two weeks.this dosing will get rid of the adult worms but you need to get the eggs that have been left by them that will eventually hatch into more adult worms. It's common to worm puppies every week starting at 4 wks of age until 7 or 8 wkswith a general wormer.there are also other intestinal parasites and bacterial infections that cannot be seen by the naked eye and your vet needs to ck the stool under a microscope so it would really be best if you take a stool sample to him in a few weeks to ck for everything. then start him on the heartworm preventative!!