Its completely normal for this to happen, osteoperosis/osteopenia goes along with CF like many other things because we don't absorb all our calcium and Vit D. I was on Fosamax originally but had horrible side effects from it and was switched to Boniva which has been fine but I have trouble remembering to take it because it's only once a month. At my last pre-transplant appointment I met with the endocrinologist and he suggested switching to either the injectable Boniva which is 3 times a year I think or to Reclast which is a once a year iv infusion. The nice things about these is I'd have it done at regular follow up appointments so nothing for me to remember and because it goes directly into the bloodstream there is no problems with absorption.