I use entirelypets.com but have never ordered a prescription med from them. Their products are said to be FDA/EPA approved though and, as far as I know, they don't get their meds from other countries. I have ordered Denosyl and none of the bubble tins had been popped.
6 Months Heartgard PLUS Blue (for Dogs up to 25 lbs) 6 MONTH Frontline PLUS Orange for Dogs 0-22 lbs