I am the immodium queen, now I am not going to say its totally ok with your situation, but I take it all the time even when I don't had D. I went on a 6 hour plane trip and did not want to get stuck in that little bathroom for more than 2 minutes so yes I did take one. I also take them before I go to work in the morning....... I am also on pentassa and was told by the pharmacist that it is ok to combine the two. I feel that I do take them too much but I think if you take one before your train trip you will be fine!! Good luck and have fun!!