Blood in stool after worming

Hello I have 2 6 week old kittens now that i am fostering, and was told by my rescue coordiantor that I could worm them. I wormed them yesterday, and today I noticed a coupld drops of blood mixed in with the stool of one of them. Is this normal? They are acting fine other wise, eating, drinking and playing normally. I wormed with Drontal cat if that helps