long term use of slippery elm

My Quincy has had a several month history of problems with fecal impactions requiring manual evacuations. His diet has been changed to not include any dry food, and he is on lactulose, 6mg day and cisipride 10 mg per day, divided doses. I also use a full capsule of slippery elm each morning in his food mixed with water.
I previously used Natural Factors Ultimate Probiotic which did not seem to have much effect, but it was during a time he was impacting every week or so, so it may not have been a fair trial. His bowels have been moving fairly well over the last couple of weeks, and I now worry about the long term use of slippery elm, of whether it will continue to be effective or is it potentially harmful. I also started putting the probiotics back into his diet yesterday since he is having regular BM's now and I want to keep it that way.
Quincy is 10.2 KG, a big boy. so I have been using about 1/2 probiotic cap in the morning meal.
I would liike to reduce the amount of lactulose he receives because he really hates the stuff and I don't blame him, and that is in my long term plan, but for the moment, is the slippery elm safe to continue? My vet did not know, and even wasn't aware of the slippery elm until I told her, so she is not able to advise me. My breeder was not sure either as she says she has only had to use it as an occasional help.
Has anyone used it on a routine or long term basis?
Thanks for any input.

Slippery elm is completely non-toxic and safe for long-term use. Many cats with IBD take it for years. The only potential issue is its ability to interfere with the absorption of other medications, so those should be given about an hour either before or after the slippery elm.

Thanks SCM. I had read about it on line and that was where I discovered that it could cause problems if not given with adequate water, so I started to increase his water mixed with his meal he gets the slippery elm. I usually wait until after he has relaxed a bit after his meal in the morning to give his other meds - nasty I know, but he is big and when doing it alone, I prefer the more half asleep version to try to get the lactulose down. The caps are never a prob, just that goopy syrup!:D

Does you think Quincy has megacolon? Here's a link:

http://www.peteducation.com/article.cfm?c=1+2122&aid=3471

Herbie hates the lactulose too. I don't squirt it in all in one shot, but a bit at a time so he can breath inbetween. When he is going through a rough time I give him 9 ml per day, 3 x 3 as per the vet, Herbie is about the same weight as Quincy.

Touch wood and all other things known to factor in.....Herbie right now is doing A1 :)