Hi Kelly,
I wanted to let you know that Quincy has been on leukeran for almost 2 years (will hit that date in May). It was primarily to deal with his lymphoma, but I've definitely seen it used for IBD too. Initially Quincy was on leukeran I think once a day (1 mg dose) and prednisone twice a day (5 mg/dose, 10mg total daily). We scaled him back on both, and now he's on 1 mg leukeran M/W/F. I have to bring him in every 3 months for blood and urine analysis to make sure there is no bone marrow suppression or evidence of pneumonia, bladder infection, or other types of infection. He's done very well on it. I have not seen nausea or really even much fatigue. It is a pretty mild chemo drug. I actually just asked my vet a couple weeks ago about Quincy being on it long term and the side effects of that, and he said cats do pretty well on it (knock on wood!).
Note I've seen dosing protocols that use more of a "pulse approach" - e.g., 5 days in a row, then nothing for 2 weeks. Also, you likely could start with a stronger dose and then taper off as we did. I know in the beginning my vet's goal was the give the cancer a big punch and then keep it at bay with as low a dose as is successful. If Quincy has a pattern of vomiting or another type of GI flare up, I can bump Quincy up to daily leukeran for 5-7 days. Last time I did that, he did seem a little more tired, but otherwise handled it pretty well.
You probably want to read more about the relative merits of leukeran for IBD vs other drugs, but I think I'd prefer it over prednisone myself if it was similarly effective.
One last thing - you likely will need to get it from a compounding pharmacy (the one I use does mail order, if you need it) as I think the factory issued size is 2 mg. Since it's a chemo drug, you shouldn't try splitting it yourself. Be sure and ask them to put it in as tiny a capsule as possible! Since it's in a capsule, it's easier to slide down. I put it in baby food and Quincy eats it without knowing he did.
