ivermectin is the active ingredient in heartguard, so yes it is safe. However, the doses from farm-bought Ivermectin are tiny.. in addition the medication, because it is in liquid form, generally has to be refrigerated, I have never heard anyone else talk about putting it in food or water with success. The only edible forms I know of are the pills.
Scrolldown a few pages in the discussion forum...there is a recipe for the liquid,even though it is the injectable type. It is initially expensive (about 60.00) but will last a long time..much cheaper than Rx from the vet.
You can purchase a bottle of ivermectin which is the key ingredient in heartgard. A bottle will run you $30-35 but can last up to 3 yrs. I would not inject the dog either. You can absolutely add it to water. The dose is 1/2 cc per 50 lbs of body weight. It is not recommended for collie breed dogs.
The recipe on the other post calls for a 50ml bottle of 1% injectable Ivermectin but once you make the mix, you give it ORALLY. I paid $28.00 for a generic brand 50ml bottle of the ivermectin and $13.00 for 1 gallon of propylene glycol. My vet says that this will last me for 2 years for my husband's 8 hunting dogs. He said there will be plenty left over but the expiration date for the ivermectin is only good for 2 years and he said I need to throw the rest away when it does expire. I would NOT put it into the food or water. You need to know for sure that the entire dose was taken in. It's such a tiny amount that it is very easy to just squirt it inside their cheek. Just trying to help.
Heartgard for dogs between 26-50 lbs. contains 136 mcg (micrograms) of Ivermectin. 1% injectable solution Ivomec for cattle contains 10 mg (10,000 mcg) of Ivermectin per 1 ml. That can be broken down to 1,000 mcg per 1/10 ml. If you want the dosage to equal the Heartgard for a 26-50 lb. dog each dose is 136 mcg so you divide the 1,000 by 136 and find you have 7.35 doses in each 1/10 ml of 1% Ivomec. Draw up 1/10 ml into a syringe or marked eyedropper. Drop by drop put it back into the bottle and count how many drops there are, divide it by 7.35 and you now know how many drops are in 1 dose. Drop sizes vary so always use the same dropper or syringe.