Combination heartworm, roundworm, flea medication

Frontline plus is what I always used too. Changed because vet advised they are seeing resistance to the frontline plus because it has been used for so many years. The fleas/tics are becoming immune to it just like some of the human meds and the new super germs with antibiotics. You may want to ask you vet about this.
(We were in the south when advised this).