Isn't nitroglycerine a common heart medication? My understanding is that this turns up false positives at the airport frequently. It is common, I think (my father-in-law carries it with him). However, if the pills were in a container, which would probably be stored in a suitcase, I don't think the dogs would pick up the sent in the car. If you put the bottle of pills on the seat, well then, yes, the dogs would probably hit on that.
My husband has nitroglycerine also, but you can't carry it around in just any bottle. It breaks down too easily. It has to be kept in an airtight container. My husband carries his in a stainless steel vial with a rubber seal and stainless steel screw-on top. Still, I think dogs could probably pick up on a very small amount of residue that could be on the outside of the vial. But nitroglycerine is not something you can carry around in a pillbox or loose in your pocket like aspirin.