Dear Susie,
For the benefit of anyone unfamilar with LD50's, I thought it would be
prudent to add that the LD50 of any substance is usually extremely far and
above most prescribed amounts, and that lesser undesirable effects can occur
far below LD50 levels [there are some exceptions in certain treatments which
certainly makes these drugs precarious to prescribe effectively].  So unless
you are calculating how to "kill" your ferret [or yourself for that matter]
with any substance, including Vitamin A, LD50 should only be used as a frame
of reference, and not as a rule for therapeutic or overall safe amounts.  I
guess what I am trying to say is that to suggest [not that you implied this
directly] that any amount even far below the LD50 is safe is not a good
thing.
 
best wishes,
alphachi
[Posted in FML issue 1879]