Please, please don't use Biospot or any other flea products from the grocery store, Walmart, etc. They can cause serious reactions in dogs, even death. Just do a Google search.
BioSpotVictims.org - Bio Spot Flea & Tick for Dogs - Adverse Reactions
Spending the $$$$ on a safe flea product like Frontline or Advantage can save you a huge vet bill.
Did you ask your vet to sell you one tube of Frontline? Some vets will do that.
Entirely Pets has great prices on flea control products:
3 MONTH Frontline Top Spot Orange: For Dogs up to 22 lbs.