The three I have on long term pain relief all have bone related issues (one of whom has arthritis). When he was dosed once a day he got a 'low' where the pain relief wore off and he would sink right down, so I copied for him what I had already mastered for Wish and Flame, and that was dosing twice a day and he stopped having his lows. Actually, I haven't seen him happier since he was neutered, which was in September 2007.
If I had another bunny with arthritis I wouldn't mess about with dosing once a day because I have found it is more effective done twice a day.