Dr. Andrew Weil...I'm not enthusiastic about the idea of taking Pepto Bismol on a long-term basis because it is a salicylate and these chemicals can be toxic. They also can cause allergic reactions in sensitive people, something I'm sure you wouldn't want to develop on an extended trip. I do take acidophilus with meals when I travel in underdeveloped countries, and you're right, heat can damage those friendly bacteria . Always check the expiration date on acidophilus products and try to protect your supply from overheating. Instead of taking medication prophylactically, be on the lookout for trouble. At the first sign -- usually sulfurous-tasting burps -- stop eating entirely. Drink peppermint or chamomile tea and use a little Imodium, which is safe and I believe is the best over-the-counter remedy for diarrhea or diarrhea with cramps.