Different dose

My almost 13 year old cat, Dillon, has been battling IBD and chronic pancreatitis for almost 2 years.  Recently he has progressed and been diagnosed with Small Cell Lymphoma of the bowel.  His chemo regimen is different than all others I have read on this site.  The vet has put him on weekly doses of Dexamethasone, and biweekly doses of Leukeran.  He got his first dose of the Leukeran 1.5 weeks ago (6mg).  He did fine, slight dip in appetite, nothing major.  His attitude and activity levels were all normal, until yesterday.  Within a few hours he went from seemingly normal, to lethargic and staggering.  I took him immediately to the area emergency vet hospital, they ran blood work to be sure he wasn't in kidney failure.  All relatively normal results.  Has anyone else had their cat on such a regimen?  If so, did they have delayed side effects this severe?  He continues to have a healthy appetite and is eating well, but the light has seemed to have gone out in his eyes.   I'm afraid, if he can't bounce back from this, that the treatment will be worse for him than the cancer. 

I am so sorry your are going through this.  I have an IBD kitty myself.  I have no experience with Leukeran but that does seem to be an unusual dosing.  My kitty was on Dexamethasone when there was no prednisolone available.  He stayed on it for about a year and began to have blood sugar issues.  The pred was available again by then and putting him back on the pred fixed the issue.

I am wondering if the delayed reaction was actually a reaction to all the meds working out of his system rather than to the meds themselves.  I would definitely ask about going back to a daily or every other day dose of the prednisolone.  I do believe it is the best steroid for IBD.