We use liquid ivormec (given oral) and have for over 12 years on 4 boxers. We have never given it without discussing it with our vet first. It was recommend to us by a friend who used it with her dogs, her sister who is a vet recommened it. Our vets have all said it was okay, we discussed what we were using and how much to give them.
None of our dogs have ever come back heartworm positive or had any problems from the ivormec. We purchase it at Tractor Supply (TSC) in the liquid form for cattle, we give 0.1cc per 10lbs of weight. We use a syringe to measure and put it on bread. My husband has a nursing license so he knows how to measure dosage but it isn't hard to do and I also give it to them when he isn't here to do it. My husband also used it for years when they had their farm with cattle.
Our dogs get tested every year for heartworm when they go in for their yearly shots.
We give it year round, the bottle of ivormec runs about 30.00 to 40.00 and lasts for 2-3 years (bottle comes with experation date) even with 2-3 dogs. There are two types of ivormec you DO NOT want to get the PLUS just the regular ivormec. You do need to discuss it with your vet to let them know what you are using and make sure it is okay for your dog (no other health problems, etc. that they have). There are certain breeds that the liquid (oral) isn't recommened for...Aussies, shepards and a couple others I think). We have never had a problem with fleas or ticks.