We decided to try the combo Bactrim & Doxy. I'm hesitant to say it will work, but I have already felt better than the past few days after only 5 doses. Is 100mg Doxy twice a day the normal amount a CF should take? This was my GP, so my CF clinic isn't until next week. So far, no side effects that I've noticed. Let's hope!! <img src="i/expressions/face-icon-small-smile.gif" border="0">