Perhaps you can get droncit/drontal from a vet. Of course it'll be for a cat or dog. I dont know the dosages for chickens using the pill form. You can ask the vet for that info as well as the withdrawal period for the droncit/drontal.
The Drontal feline tabs (Praziquantel-Pyrantel) I have are dosed 1 tab for every 4-8 lbs.