I have been using Zimectrin (Ivermectin) for my dogs for 20+ years with NO problems and NO worms of any kind. A once a month wormer that takes care of round, hook, tape and heart worms. You can buy it at most Tractor Supply stores and other co-ops. Yes it states horse wormer but it has the same active ingredient, 1.87% Ivermectin, as most dog worm meds. The medication is a paste with a syringe that will allow you to regulate the amount of med's that you dispense, by the weight of the dog. The cost is between 6 to 10 dollars per syringe and treats 1250 lbs.