Prescribing IV medication for inhalation is nothing new. Gentamicin and Tobramycin IV (not TOBI) have been prescribed for as long as I can remember. Personally, I started using them in the early 90's.
I think the downside is that you're using a drug "off label" and insurance companies frown on that. So do some doctors. Also, I have to pay my IV co-pay price for my "inhaled" IV drugs as well, and for me, that's more expensive, about $100/month. Another downside I can think of is that there are few to no studies about the side effects of each particular drug being used in this unconventional method.
Piper, the Aztreonam I'm using is IV Aztreonam. I started using it 4 years ago. I'm willing to bet my doctor saw the AL study and thought, "well, in the meantime I know some patients who could benefit from this drug RIGHT NOW, so why wait for AL." I'm totally making that up, but maybe it has some truth.
Another note. I'm using these unconventional methods (aztreonam IV and ceftaz IV) because I'm allergic to Colistin and I don't respond well to TOBI. Oral antibiotics might as well be candy, they don't do anything for me anymore, none of them. So other than IV antibiotics, this is all I've got. And for me, it works really well.
You do have to get a doc that will prescribe it though. It is off label use. I never had to ask for it. My doc suggested them.