Flea treatment issues

[Tom_C76]

We seem to have a recurring issue with fleas. Have two rough collies, both dosed monthly with Effipro. Smaller dog weighs 18kg so gets the medium dog pipette (10 to 20kg). Larger dog weighs 26kg so gets the large dog treatment (up to 40kg, so much larger than he is).

Smaller dog is free of fleas. Larger has lots of them. Seems as though the treatment isn't spreading on him for some reason rather than being fleas that resist the treatment, as otherwise I'd expect both to have the same issue.

Any suggestions as to what to try next? Flea combs or regular baths are a non-starter with a particularly hairy rough collie.

[Tom_C76]

Advocate was recommended and dispensed by a local vet. I didn't use it as the worm treatment in it is very toxic to collies by ingestion, and I'm not going to risk one licking it off the other.

Will look into the other suggestions, but I'm baffled as to why the fipronil is killing/preventing fleas on one dog and not on the other...

[Tom_C76]

Just to follow up, and with thanks to Bex for her comments, we took both beasts along to a different vet who has prescribed Bravecto tablets. They agreed that dog No 1 wasn't showing any signs of fleas but we're treating them both with the same stuff anyway to help with tracking when it's due.

Advantage of this stuff is that it does work on ticks too, which are a major issue round here due to the deer population and grass in the parks not being cut very frequently.