Frontline is an old chemical now and we do see a significant number of cases where it doesnt seem to do the job. It is also a significant cause for concern due to contamination of waterways and damage to invertebrate life.
The newer products containing Isoxazoline based compounds (Bravecto, Simparica, Nexguard)are forming the mainstay of flea and tick control products now and work well and seem well tolerated. In addition they are largely faecally excreted and are of less concern as far as waterway contamination goes.