Are you certain it are fleas causing the itchiness for Tramp? If he's allowed out and has access to long grass & trees, it could just as well be harvest mites - though it's just about the end of the mite season now.
From what I've been told (vet & FAB) Frontline is the dosage of choice, but my experience with Pearl is that while Frontline reduces by some way the number of mites latching on, it does't get rig of the little blighters entirely.
If you can, I'd check Tramp's belly and toes (specially in between) and look for little orange spots just in case. If you do see some, then it is harvest mites that's causing the itchiness and well, there's not really that much you can do - rubbing affected areas with surgical spirit does help though.