There is still no proof that fleas are becoming resistant to frontline, but there is screeds of anecdotal evidence. I suggest to all my clients that they alternate their flea treatments from packet to packet. Farmers have been doing this for years to prevent resistance developing. I'm assuming you only have one pet in the house and he has been treated as recommended before this last treatment ( ie monthly) ?
PS I'd recommend giving Advocate a go, but it's not really stronger, only different. It treats against all worms except tapeworms, so if your cat is a hunter you will have to treat separately. But it doesn't do ticks, which Frontline has some control over.
Frontline DOES work. When flea eggs in the carpet hatch into larvae, then become fleas, they jump onto the cat and can take a while to die. in fact will only die if they take bite from the frontlined cat.
The Program injection is the best thing ever - though I think a lot of vets cottoned onto the fact that it lasts & they lose sales on other anti flea tuff, so it can be hard to find a vet that does it now
it works by sterilising the fleas when they feed, so they don't breed & you never get an infestation again.
When it first came out I had both of my old cats done with it after a really bad infestation, so bad that DH turned into a big screaming girl as walking passed the cats favourite spot in the attic had his hairy legs COVERED in them - it was awful they were everywhere & we didn't think anything was going to work bar DDTing the house - or moving out
had the jabs done, no other treatment needed & fleas all gone in 2 weeks & never came back - EVER
a few years later & my old cats have passed & we now have 2 rescue cats - we found it much harder to find a vet that did the jab & when we did, they told us it only lasted 6 months
our old cats lasted years - I thought perhaps the formula had been changed, but thought we'd wait & see if our current cats did get fleas before going back for the booster -
nearly 2 years later & they've not needed another jab, so it does look like it might be just sales pitch
Program is really good - and worked well on our last cat. This cat has a flea allergy which means although the fleas die quickly if they get onto her and bite, its too late and she comes out in scabs. Program doesn't prevent fleas from getting onto the cat so we've had to go back to drops (either frontline or advocate).