
puppies get half the adult dose daily for 3 days so that is 0.5ml of Panacur 10% suspension per kg of bodyweight and should be done monthly to 6 months.
As he hasn't been done properly before I would do as suggested and worm again in 3 weeks, and then monthly.
I have wormed bitches in pregnancy for 6 generations and their pups twice by 7 weeks, and have never seen a worm.
A friend took in a rescue GSD litter at 6 weeks with typical staring coats, dull eyes and pot bellies. they were so anaemic from a huge worm burden that they also had hardly any appetite. She very nearly lost one bitch.
So a low worm burden may be no big deal but a heavy worm burden can kill puppies or cause life long digestive issues.
The granules work out loads more expensive.