The reason for giving HW meds monthly is because unless you are very vigilant and organized it is very easy to forget when the 45 days is up. Even if you put it on a calendar somewhere it is most likely, with all the craziness that comes along with living your life, that you will forget to check your calendar. You always know when the 1st of the month is. That was the reason for the original recommendation of monthly HW meds. They knew that it was easier for people to remember the 1st of the month. Another reason for the necessity of the yearly HW test is because there is no medication be it for humans or animals that is 100% guaranteed. You do not want to give heart worm meds to a dog that could possibly have an active case of heart worms. As I said, better safe than sorry. HW test is much less expensive than finding out that my dogs have active HW but I chose not to spend the money for the test. Also the test is much less expensive and the meds are much less toxic than the expense of the cure and toxicity of Heart Worm cure.
