I have a Lemon Tick Beagle who will be 3 in September. I've given her Frontline Plus and Heartguard since we got her at 6 months old. Last month, the Vet changed to selling K9 Advantix II and no longer carries Frontline Plus so I gave her the K9 Advantix II. She didn't like it when I put it on and reacted negatively which she didn't do with Frontline Plus. She hid under the bed for a few hours but seemed to be fine afterwards. I noticed throughout the month a change in her personality. Crying (whining) for no apparent reason and she is not as active or friendly at the dog parks. Yesterday, I had to remove her from the dog park as she growled at another dog at the water bowl -- which she has never done. She usually steps aside and waits if there is another dog near the bowl. And another dog owner said she growled at her dog also which I wasn't sure if it was her or not. So, I've noticed a distinct personality change. Also, when we got to the dog park she was not cooperative and was pulling and crying trying to get in. It took 20 minutes from the car to the entry to get her to behave in an acceptable manner. Even then, she didn't behave like she should and has achieved in the past.
I would appreciate any suggestions/comments you have. This is my first Beagle and I know they are all about the smells and harder to train but I feel I'm going backwards and I also suspect the medication to have changed her personality a bit.
K-9 Advantix is definately stronger and some dogs get skin reactions from it. They can act funny after the application because they feel so uncomfortable. Your beag should be fine once it settles in on her. If she still acts funny after a few days you should call the vet. I am using Frontline Plus, I order it on Healthypets.com for a good price. Pet stores sell it also.
For heartworm meds I use liquid Ivermectin once a month mixed with their food. It is very affordable compared to some of the other brands.