User blog comment:FairyRaven/Fairy Tail Chapter 471: Until the Battle is Done, Review and Commentary/@comment-210.4.100.122-20160204053229/@comment-7418318-20160204085226

While the Magic Barrier Particles have similar effects as poison, they aren't actually a classical poison. They damage the body by attacking their magic or somesuch, which means that they are most likely as harmful to Mirajane as they are to anyone else.

And that's assuming that Mirajane can "suck out" the particles from Laxus in the first place. Breathing in a poison cloud is quite different from dislodging particles embedded in a bloodstream or maybe even stuck to organs.