Luvntzus -- don't use Biospot -- first off, it lasts less than 2 weeks, BUT the big 'baddie' is that it's systemic. It goes thru the skin into the dog's bloodstream and stays there (even when the benefits have worn off, part of it is still there). There have been numerous cases of small dogs reacting very very badly to it. [link
http://www.dogsadversereactions.com]http://www.dogsadversereactions.com[/link]
If you want something more cost effective and yet really flexible to dose why not try Frontline spray? I use regular Frontline on Billy and Luna and it works well, but it doesn't on Kee Shu (peke). But the Frontline spray works very well on her and lasts the month.
You're supposed to 'dose' it at 1 spray per pound but depending on the time of year I often don't use that much (and I'm in Flooooor-da -- flea capital of the world except maybe for Texas!). But it's far cheaper (it's about $26 for the spray bottle and I've never used it up yet and have had it two years).
Good luck.