Hi
@Deagle113 when a dog is on common medications such as flea and tick prevention, heartworm protection, antibiotics and so forth is there any risk of these medicines being transferred to a human via oral or sexual relations and if so is it dangerous?
Good question.
It depends on the medication in question and the form that it is being delivered as to transference, but generally these things are designed for animals in close proximity to humans, and many of them are identical to the stuff already used in human medicine, so I wouldn't worry too much. I will address the topical stuff though, because that is a very common question I get asked in clinics.
Regarding the topical spot on stuff like Frontline and Seresto collars, which were mentioned, both work by diffusing oils that are incorporated into the hair follicle itself and released over time. These are essentially both are pesticides, which kill or impair ticks (and fleas, and other guys) on contact. Frontline is made from Fipronil, which is also used in agriculture and for indoor pest control, and WHO lists it as moderately hazardous, but there's not a lot of research on it's effects on humans. The other major tick-preventing pesticide, permethrin (which is found in stuff like Advantix), is a component of medications already in use for people, like lice rinses and scabies preventatives--there's even permethrin releasing clothes now.
Seresto collars specifically contain Imidacloprid and flumethrin in combination. Imidacloprid is an insecticide that acts on specific receptors of the central nervous system of things like fleas, leading to CNS impairment and death. These receptors in insects have a much higher affinity, or desire to bind, to imidacloprid than to similar receptors of vertebrates like cats and dogs, thus the preferential action.
Flumethrin is a pyrethroid insecticide that conveys its action through voltage gated sodium channels in nerve tissue. Its action leads to repeated nerve impulses that lead to death of the insect. It also has a very high affinity for invertebrate nerve tissue over vertebrate, as the key to the safety of both of these is their preferential binding action. The big danger with seresto collars is chewing on them and ingesting large doses, so keep them away from mouthy companions.
Regarding the anecdotal seizure reports, which I run into from time to time with clients, I have yet to find any substantial evidence for the correlation. Even if seresto collars cause adverse effects, they are not seizures. The most common reaction is dermatitis (inflammation of the skin) at the contact area. There have also been occasional cases reported of intoxication as a result of dogs ingesting the collar as I mentioned, dogs overdosed because the wrong-size collar was used, or dogs being unusually sensitive--adverse signs have included tremors and lethargy, but not seizures.
Seizures as a whole have many potential causes are are very complex and difficult to resolve -- we vets even have a term that means "we tried everything that we could and know how to do and we still have them and can't figure out why yet" --- Ideopathic seizures. They are scary to watch, especially when they happen to a loved one, and not having a solution feels powerless and frustrating both to the docs and to the guardian. It can be easy to try and find an explaination but there may very well not be one, at least with the current state of veterinary science.