Funny you should bring up mirilax! I just saw a new doctor (urologist) for the UTIs I am now getting from Tysabri. One of my instructions from her was to use it because constipation is a risk factor for UTIs (according to her). She said it is imperative that I have a bowel movement everyday. Easier said than done. The first night Mirilax worked like a charm. The next few nights not so good. But I've been on antibiotics which are making me regular so I have stopped the "antifreeze" for now.