I used Vector 3-D last year after Frontline did less than nothing and didn't have a single problem with it. Both dogs were fine with the medication itself and I never found a single flea or tick on them afterwards.
Before hand, the fleas were so bad that I was getting bit just sitting in my office and this was with Frontline! But after a good bath, the Vector and vaccuming Borax into the carpet, they were gone.