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I will try to clear up some of the confusion about Frontline, ear mites,
and rabbits.
 
Frontline when applied to the skin (or inside the ear) is not absorbed
into the bloodstream, and it does not cross the blood/brain barrier in
ferrets.  Thus it does not cause any problem with the ferret's GABA
receptors, because it stays on the oil layer on the skin (or ears).  Only
rarely does Frontline cause any skin irritation on dogs or cats, and I
have not seen this problem in ferrets.  There was a study with Frontline
for ferrets (Lewington, J: Frontline for ferret fleas.  University Sydney
Postgraduate Foundation, Veterinary Science Control Therapy Series
189:856, 1996).  Both safe and effective.
 
Similarly Revolution (selamectin), Ivomec or Acarexx (ivermectin),
Milbemite or Interceptor (milbemycin oxime) can all be used to treat
ear mites in ferrets.
 
Now rabbits are different.  Rabbits produce a large, layered exudate
("ear canker") in response to ear mites.  This is probably due to the
fact that rabbits have heterophils instead of neutrophils.  If you clean
the ears out, then they will bleed.  If you then apply Frontline to the
ears, then it may go into the bloodstream and cause problems.  Also
rabbits have very thin skin.  The alcohol content of Frontline spray may
cause them problems, and some Frontline may be absorbed thru the skin
and into the bloodstream.  This could cause problems, but I have not seen
any side effects with Frontline in rabbits either.  I used to use the low
dose (1 spray per pound) for ear mites and fleas.  I would treat the
bunny then recheck the ears after 4 weeks.  By then most of the ear
exudate is no longer there.  Cleaning the ears at this stage did not
cause any bleeding.
 
There was a paper using Frontline spray on 50 rabbits at 3 sprays (3mls)
per kg for ear mites with no side effects, but there have been some
reports of side effects in rabbits.  Currently I use Revolution for bunny
ear mites and Advantage for bunny flea problems, just to be on the extra
safe side.  Perhaps some rabbits are different and Frontline can cross
those rabbit's blood/brain barrier.  However just remember it does not
cause side effects in most rabbits.
 
The big picture is Frontline is safe for ferrets, and the spray version
is the most cost effective way of treating multiple ferrets with fleas
or ear mites.
 
Hope that helps,
Jerry Murray, DVM
[Posted in FML issue 4398]