I have only recently switched our dogs over to Trifexis and have been happy with the results. They had previously been taking a combination of Comfortis (fleas) and Heartgard Plus (heartworms & intestinal parasites). Normally I am hesitant to switch to a product that is new to the market, but am comfortable with the combination of active ingredients, both in efficacy and safety.
Our vet dermatologist recommended Comfortis to us 4+ years ago. We live in an arid climate at a higher elevation, in other words a place where fleas can't even complete a lifecycle, but we still had to deal with flea exposure since we travel to California frequently as do our neighbors with their own dogs. All it took was one flea to hitch a ride back (even on a neighbor's dog) for our boy with flea allergy dermatitis to start having problems. With the frequency of bathing and swimming for the dogs, the spot-on treatments weren't as effective as we hoped. We always make sure to give the Trifexis tablets with their breakfast and have not had any adverse issues to report (same routine we followed with Comfortis).
More information can be found at:
http://www.trifexis.com/default.aspx Including the product label:
http://elms.xh1.lilly.com/trifexis-product-label.pdf