Cellcept was my miracle drug! But I didn't take it with Arava so I can't really help you - don't recall anyone here who's been taking both, but hopefully someone will read this who can help you out.
I do know -- he'd better be watching your liver function!! And you should make sure your water intake is good.
Lynnwood, Lupus & Sjogren's Moderator, Dx: 2000DIAGNOSING LUPUS & HW's LUPUS 101
"Life is far too important to be taken seriously." - Oscar Wilde