I do not know for sure as I'm nowhere near as experienced as others, but I would think not. Not only do most people administer both at the same time, but there are quite a few products that give heartworm AND flea prevention in 1 pill or shot.
Some examples: Advantage Multi, Revolution, Sentinel.. maybe others but I can't think right now. Sentinel is highly used and Revolution is popping up everywhere as well.
I never heard except today in the same place as you about administering them at the same time being bad. Maybe someone else has more insight on that. |