I'd not even heard of it, so did a search and found this:
http://www.discountpetmedicines.com/...-heartworm.htm
It sounds like a new product. Also addresses heartworm, so if you switch to this, you need to make sure you stop any other heartworm treatments; not good to double up.
Were you using Frontline Top Spot, or Frontline Plus?
I use Frontline Plus; it kills both adults AND flea eggs and larva. Frontline Top Spot does not.
Since you said you are having issues, I just wondered which Frontline you had.
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