Just gave my 4 1/2 old brittany her interceptor green. And now I am seeing dead round worms in her stool 2x this am. Is this normal?
Last check up prior they did a stool sample and it was negative. I asked of they need another one at last exam and they said no. she was at the vet on Friday and is gaining weight beautifully . She is 21 lbs.
should I call the vet?

My dogs were very ill and at the vet, staying over a few nights. I was very confused and upset when they did a fecal test and it came out negative, but the naked eye could very clearly see worms in the stool. I am going through the same thing yet again, (taking a stool sample in today with little to no faith to the accuracy of the test) but this time there is no visual of worms, just running yicky poop. That being said, there are many other things the fecal sample is tested for, so it's always a good idea. Did your vet tell you, that 2 weeks after the treatment, you must re-do the de worming? (The first vet left this part out, so I had to treat yet, AGAIN and that is x 5 dogs) Always call the vet with a question you have regarding your baby, my vet doesn't even have to ask my name anymore, they know my voice! The vet I go to now, is on the ball.. and doesn't just tell me to "bring her in" with every thing that happens (this really makes me trust that they are not after the money, yet REALLY care about my babies) but the calls will put your mind to ease. Any vet with a true heart wouldn't mind you calling with questions, and the VET (he or she) should call you back themselves! (My new Vet does return all of her own calls, amazing!) Maybe have your baby checked for heart worm, etc just be on the safe side. I wish you the best.

That sounds normal to me. Only 85 percent of all negative fecal are truly negative. Keep her on her Interceptor. The interceptor is just getting rid of the worms. It's a good thing. If you see small white worms that look like rice or coconut in her stool she will need a different wormer for that. Those are called tapeworms. Hope this helps :)

Update: Jody is fine , only a few round worms yesterday. Stool is fine today .
Thank you for all of your knowledge and advice. And Jody thanks you too.