Like many, I was concerned about just what exactly was happening in my lungs when Afrezza is put into it. I'm especially attuned to this question having followed some injectible "ultrafast" insulins being developed, and the biochemical techniques used to speed absorption.
The way that stuff works scares me when lung tissue is in play.
Fantastic news about Afrezza: The "magic" is nothing more exotic than a purely passive, non-chemical approach. Further the carrier, Technosphere (Mannind's invention) is composed of only N, O, and H in a very simple molecule, fumaryl diketopiperazine (FDKP -- name sounds scary, but then so is dihydrogen oxide if you don't know that that's H2O). The key is the mechanical folding of the molecule, which makes it fairly porous. Insulin sticks to it, but Technospheres generally don't like to stick to each other, so they don't clump and are easily dispersed into an atomized cloud.
Afrezza gets it's remarkable pharmacokinetic action simply by maximizing the spread of insulin over the entire alveolar surface area evenly. This allows for a very large immediate flux (flow rate) of insulin molecules across the type I pneumocytes enclosing an alveolus.
What happens to the FDKP molecule post-administration I'm still researching. However, according the literature available that I've found so far, it is not metabolically involved at all, so I'm guessing right now that it simply breaks down into water and Nitrogen gas, and is absorbed without issue.
So, what is an Afrezza particle? A tiny little sponge made from a loosely folded up FDKP molecule, soaked with Humulin. That's it.
The remarkable behavior of Afrezza is due entirely to how it effects the distribution of the insulin-bearing particles so that they provide the maximum exposure of the lung surface to the insulin when inhaled.
Some numbers and illustrations to reference in thinking abou all this:
Technosphere diameter: 2µ (microns -- millionth of a meter)
Alveolus diameter: 250µ ; inside surface area: 200,000µ2
Technosphere particles completely coating inside of alveolus: 50,000
Alveoli in typical lung: 70,000