One website I read that was written by a doctor said he always dosed his patients up on like quadruple dosage probiotics when they were on antibiotics, then like double dosage for several weeks afterwards. Wish I could find the page again, but that was my first introduction to probiotics.
I'd certainly try upping the dose if I was on antibiotics. In fact, I take Culturelle when I'm on them because that's really strong for me (if the amount of gas is any indication), then drop down to yogurt and/or acidopillus pills for three weeks afterwards. That's for regular antibiotics mind--not more than one type, and nothing very strong.