Can IV Decadron pre-med make Irinotecan less effective?

My daughter gets a pre-med of IV Decadron prior to getting her Avastin/Irinotecan meds.  This was primarily introduced to help with her nausea.  She only gets it once every 2 weeks.

A person on a pediatric board that I post on mentioned that her daughter's Dr., Dr. Finlay, mentioned that getting Decadron via IV within 1-2 hrs of Irinotecan could lessen the effectiveness of it (Irinotecan).

I know that Dr. Finlay is highly respected, though my daughter's Dr., Dr. Phillips (CHOP) is highly regarded as well.  I literally trust him in full with my daughter's life!

Has anyone heard of a study that proves this theory?  Now I'm getting nervous that maybe this is a reason her tumor slowed down (shrinking).  Her next treatment is tomorrow and I will be bringing it up to them, however just wanted some additional info to bring along. 

Thanks!
Meri
m/o Caitlin, 6 yrs old, dx 7/30/08, AA3

From what I am able to read, CPT-11 lowers the white cell count sometimes, and the only interaction with  dexamethasone is that the dex can sometimes make this effect more pronounced.  It's pretty routine to get dexamethasone with Avastin - CPT-11 from what I've read, that's what I'm getting.

I have never heard of the connection but, in layman's terms, I believe it's hje Avastin that shrinks the tumor by cutting off its blood supply. The ironotecan is used to kill any cells that are left behind. If the dex makes you nervous, ask her doc about it for sure. I doubt he'd be giving it to her if he believed it was affecting her treatment, but there are other anti-nausea meds he can prescribe. By the way, I was told the effects of dex are out of the system in 72 hrs (which is why we don't become addicted to it with every 3 week infusions the way we do with daily pill doses. My heart goes out to you and your little sweetie. Any mother's heart would.