I heard you are not suppose to use Frontline on Ferrets.  Just Advantage.
Make sure if you are using the dog strength, you have to use less.  Make
sure the concentrations are the same.  I use the cat, under 9 lbs.  There
is a link for cheaper advantage, 4 tubes for 19.99.  Shipping not bad
either.  Here is the link: www.petshed.com
 
Marguerite (The Internet Queen of Finding Good Deals!)
And her Crew
10 Fuzzy Ferrets
12 Fuzzy Ferret Rescues
[Posted in FML issue 4339]