For anyone considering using this for an affected cavalier -- I have seen a 100% improvement for Leo with this on his very first dose and wish I'd started him sooner.
From regular hard scratching sessions especially late night/first thing on waking, plus a few sessions through the night, he has gone to minimal scratching sessions and just seems so much more lively. He hasn't scratched at all during the night.
He's on the minimal dose so I'll see how he does. For anyone with an affected cavalier I really strongly suggest looking into using this to relieve pain and discomfort. NSAIDS (eg rimadyl) had done nothing at all for the scratching that I could see.