
I'd wait to 7 weeks. I do mien at 3 and 7 as Mum is done in whelp and Panacur is normally given at monthly intervals, and I suspect the closer dosage is aimed at pups that are likely to be wormy (when bitch isn't treated in pregnancy).
Years ago when vet dispensed the Panacur I was told to worm at 4 and 8 weeks, and all was fine, a couple of litters later I got the packaged product and wormed at 2 1/2, and 5 and had terrible raging diarrhoea, when I did them at 5 weeks.
Ever since I have only ever done them at 3 and 7 (so the tums are settled before they go), and advise doing again at 11 weeks and monthly to 6 months.
I believe Drontal is given two weekly as it isn't' effective in immature stages as the Panacur.
In all my dog breeding years since my first litter in 1995 I have never seen any evidence of worms in my puppies or adult dogs.All my adults get wormed when a bitch comes in season before mating, and when all the pups have left, and twice a year, if the above doesn't cover that.