I understand your frustration. I do not buy these meds from my local vet for the same reason. They try to pull this with me all the time. I have a holistic vet (about an hour away) that also practices western medicine. She told me that you don't need to do the yearly or bi-yearly ck for heartworms if your pet has been on the medication. She does not require me to bring them in, I just call her and she mails me the heartworm meds I need. She told me thinks the blood checks are a scam for other vets to get more money from you.
The companies that make these drugs say they have guarantees. If your dog is on the medication as prescribed and they get infected, they will pay for the vet bills to get the worms out. That's what the local vet told me anyway...and why they say they require you to do the blood checks.
My holistic vet also told me that you do not need to give them the medicine exactly every 30 days. She told me that I can give it every 6 weeks. She thinks the dogs are being over medicated as it is, but it is important to protect against heartworms and parasites, so we have to give them these meds. Double edge sword.
The lifecycle of heartworms is 3 months from egg to full grown so even if there is a short lapse in the meds, they are strong enough to kill what might me in there, if it's administered within the 3 months and not fully grown worms. She only medicates her dogs every 3 months. I am afraid to take that risk, so I administer every 6 weeks. I figured that she's a vet and can take care of an issue if one arose in her own dogs.
My mom lives on a farm and uses the meds you can buy at the farm stores. She hasn't had any problems. Have you checked Farm and Country or someplace like that?
My cats are not on any heartworm meds. They are indoors. The vet (local and holistic) told me if they stay indoors, they don't need it.
I don't know about buying them from over the internet. You are taking your chances. I have thought about it but am afraid they might be low quality.
Do you use anything for fleas? The past few years I have been using a little garlic (**be careful with the garlic, too much can be toxic) and brewer's yeast mixed into the food. Then at bath time I use Dr. Bronners and some citrus oil. There is only 1-2 months I have to use Frontline. Usually around Sept./Oct. when the fleas are uncontrollable.