A 19% difference in the discontinuation rate for Afrezza compared to usual care is not the sign of a therapy that is well liked or tolerated by diabetic patients. Adverse events related to Afrezza caused the sharply higher discontinuation rate, according to the version of the study published in Diabetes, Obesity and Metabolism. The study authors explain Afrezza patients might have abandoned the study in larger numbers because they were forced to use the inhaled insulin instead of injectable insulin, even if it was making them cough. This is hardly a ringing endorsement for the tolerability of Afrezza. Three outside authors on the paper received consulting fees or other payments from MannKind. Four additional authors on the study paper were MannKind employees. Afrezza caused depressed lung function over two years compared to usual care. Despite the finding, the study authors (all with financial ties to MannKind) conclude, "We do not consider the observed small, non-progressive lung function changes to be clinically significant." Of course, FDA is the only arbiter of safety that matters, which is why the ongoing lung-safety study MannKind is conducting but never discusses is so interesting. MannKind CFO Matt Pfeffer did not respond to an email seeking comment. The chart above is reprinted from the lung-safety study results published in Diabetes, Obesity & Metabolism. It shows a statistically significant, 34 ml relative decrease in forced vital capacity for Afrezza compared to usual care after 24 months. The same chart shows a 37 ml drop in FEV1 (forced expiratory volume at 1 second) for Afrezza relative to usual care, again statistically significant. The study also showed 5.75% of Afrezza-treated patients with a 15% or greater loss in lung function (as measured by FEV1) at 24 months compared to baseline versus to 3.28% of Usual Care patients. Statistically significant reductions in lung function attributable to a chronic, lifetime drug like Afrezza raise serious and troubling safety questions. MannKind may be able to assuage these lung-safety concerns when it reports data from the ongoing study in 2015. Until then, it's hard to imagine FDA approving Afrezza. -- Reported by Adam Feuerstein in Boston. Follow Adam Feuerstein on Twitter.