I nebbed Colistin for a long long time. I think ever since the neb solution came at the market. First in these yellow boxes. After that I got it from Grunenthal, that is still on the market, at least overhere. And very handy as they have all in one. A box with a vial of saline and a closed vial with the powder that you can only go in with, with a syringe.
I never got any reactions from it. No SOB, didn't need inhalers before nebbing it.
Like everyone said before. It is best to put the water in the vial a bit slowly. Don't inject any air in it, only the (for me it was 3 ml) water solution (with Grunenthal that is water for injection combined with saline). And I always used a long needle on the syringe, a needle of 5 cm. This way I could move the needle around at the bottom of te vial in case I got any powder that didn't dissolve right away.
Don't shake it but gentle move the vial around.
Let it sit for a little in case of any foaming.
Then just get it up out of the vial with the syringe and put it in your neb, also kind of slowly. Also, some nebulizers produce more foam than others.