Hi, Ann ~
Our 14-year-old cat, Bob, also has megacolon. He was first diagnosed in January of 2008 with such severe constipation that surgery was recommended. My husband and I felt that surgery was an extreme option, and we were fortunate to find an internal medicine vet who was able to deobstipate Bob when two of our regular vets couldn't.
For a year and a half after Bob's diagnosis, we had him on Cisapride and Lactulose along with regular home enemas. To call it a challenging time is a bit of an understatement, but we did what we needed to do. As we were doing more internet research about chronic constipation and megacolon in cats, we found this very helpful web site:
http://groups.yahoo.com/group/Feline_Megacolon/
There, we learned about the use of MiraLAX (often called MiracleLAX by members) to treat constipation and megacolon in cats. In early 2009, we started Bob on MiraLAX, along with guar gum and psyllium powder, sprinkled on his canned food. We were gradually able to discontinue the Cisapride, Lactulose, and, best of all, the enemas. For the past three years, we’ve had Bob well regulated on just the MiraLAX and fibers, a much easier process for Bob and ourselves.
Since MiraLAX is a dose-to-effect medicine, we kept upping Bob's dose until he was having very soft BMs, almost diarrhea. And then we started gradually adding the fibers to his canned food to firm up his stools. Bob is a large cat, weighing almost 16 pounds, so our doses of both MiraLAX and fibers are fairly high doses.
Ann, this dosing routine has worked well for Bob and us. If I can be of any more help, please let me know.
Take care,
Eva