Before you give your dog any heart worm Meds get a blood test. More than one dog has died from taking Meds. without a blood test. If you are using Heart Gard and forget it for a month get your dog tested before you resume the pills.
I have used Zimectirin for several years - - - Friend of mine has a brother that is a vet and feels it is the best for dogs but the amounts are so small the manufacturer has never gotten it approved as they feel the market is to small to pay for the testing but can be used " off lable" under the direction of a vet.
The syringe is labeled for a 1,200 lb horse so devide the 1,200 lb by the weight of your dog and dose accordingly. ( a 50# dog would give 24 doses ) on a German Shepherd it takes about the size of a pea and the dogs like it. Place on your finger tip and rub on the dog's tounge they will eat it right down.
I pay over $1,000 dollars for 8 week old registered setters. They are shipped air from Oregon not cheap. I spend weeks training them. Every bird that is shot over them makes them a little better . I can not afford to take a chance on saving a few bucks on worm meds.