I've bought it from numerous websites but surprisingly, found it is cheapest at Cherrybrook (where everything else is more expensive!) Here's a link to it there...it is also less expensive overall that Frontline, Advantix etc. It's made by Sentry...you may be able to find general information for it on their website.
The only complaint people have had is the strong clove smell, which bothered one of my dogs slightly for a day -- we didn't mind it at all, and treat three of them with it. Some dogs do seem to object to the strong scent though. I would never use any dose other than the one for up to 15 lbs, no matter what your pups weigh. That has worked on all of ours.
Here's the Cherrybrook link:
http://www.cherrybrook.com/index.cf...Defense_Flea_and_Tick_Squeeze_On_for_Dogs_3pk