> toys, etc., etc.--- and the only other consistent variable (is that an
> oxymoron?) that popped into my head was the Interceptor. It seems like
> we've altered nearly everything else that can be altered. I'll check
Diethylcarbamazine (Filaribits, Carbam) is still available, so you have a
heartworm option if you choose to do a trial run of several months w/o
interceptor. Interceptor has some of the same side effects as ivermectin
(Ivomec, Heartguard, Zimmectrin) in large doses (this info is somewhere in
the fine print on the doctor-side labelling of Interceptor). But in the
studies it took a very large dose, and you didn't describe the "usual"
symptoms anyway. An individual dog can have an indiosyncratic reaction to
just about anything, so it would be worthwhile to do a trial without it.
You'll have to decide whether to wait for winter or to try the Filaribits
or Carbam; Filaribits need to be given daily, so need to be started very
soon after you discontinue the interceptor. If you have a hard enough
winter to be safe without heartworm prophylaxis, that might be the way to
go (iirc we used to use filaribits only in the spring, summer, and fall
back in the '70s).
Keep on trying, and let's hope the irritant is something you *can* get rid
of and do without.