The time it takes for worm medicine to kill the worms in your dog will depend on how bad the dog has the worms and what type of worms the dog has.
But when you give the dog it's first dose of worm medicine it should start taking effect within 12 hours but it could take a little longer depending on how bad the infestation of the worms are in your dog.
The dog should be fully worm free within a few weeks to a month after giving the dog the worm medicine.
You should take your dog to the vet to get a fecal examination and other worm examinations to find out whether the worms have died in the dog.