Hello, thanks for your question today! I am Dr. Drew, and I am a licensed veterinarian. I'll be happy to help you in any way I can.
The active ingredient of Fiprospot is fipronil,
which is a very safe and well tolerated product in dogs.
However, any product can sometimes cause some lethargy for 24 hours or so, after application.
the hot feeling is not typical, though, and might suggest a fever,
so I'd wonder if there's something else going on, such as a viral infection.
Also, if she's received any vaccinations recently, there could be a mild fever and lethargy as a result.
if Fern is eating and drinking well, then I'm less likely to get too worried about this,
but if she's not eating or drinking, then seeing a veterinarian might be a good choice.
If veterinary care is not an option, then you could potentially try a dose of aspirin, dosed at 5mg per pound of body weight / 10mg per kilogram of body weight.
This may help reduce the fever and make Fern feel a bit better.