**6.1 Absorption enhancers**

Cyclodextrins has been used as pulmonary absorption enhancers [157]. The relative efficiency of cyclodextrins in enhancing pulmonary insulin absorption follows the following order – dimethyl-β-cyclodextrin > α-cyclodextrins > β-cyclodextrin > γ-cyclodextrin > hydroxypropyl-β-cyclodextrin (**Figure 19**). Lanthanide ions are also effective in enhancing pulmonary insulin absorption [158].
