You definitely want to double maybe even triple the dose. MY son had repeated bouts with diarrhea when he was little. Our specialist recommended Immodium AD, it really helped. You would need to check with either your doctor of a pharmacist for a doseage. Just last week my son was hospitalized with the flu. I kept him out of school for an entire week. The Sunday before he went back he got serious diarrhea and it lasted 3 days. The Immodium AD helped immensely. I beclieve it has kept my son from becoming dehydrated on many occasions.