[von Ryan]

The reason you have diarhea is because the antibiotic pwns the bacterias you have in your digestive tube. They don't do any harm to you, some of them even produce vitamins! So, when you kill them, the amount of food that was not used in your intestines is a lot larger, so, you go to the bathroom more times... In the end of the treatment w/ antibiotics, ask your doctor for something that help you get your intestinal flora back...