The antibiotic Cipro! As long as you are not allergic to it. You can buy it over the counter in most Asian countries. At the first sign of diarrheas or even loose stools I take 500 mg Cipro for two days. I got dysentery in Thailand/Laos and I'm pretty sure it was from a "western restaurant" since that's where I had my salad at. I ate plenty of street food but it was all well cooked in front of me. Waited wayyyy too long to admit it was more than travelers tummy. Now as soon as I get the runs I take Cipro and it stops it right away. Probiotics etc. are great and I always take them when traveling. But Cipro is my first stop at a pharmacy so I have it as needed.