Insulin is typically available as subcutaneous or intravenous insulin for the treatment of diabetes.
First inhaled insulin which was approved was Exubera.
Exubera is a powdered form of recombinant human insulin, delivered through an inhaler into the lungs where it is absorbed. However a longer acting basal insulin by injection.
Exubera was however discontinued by Pfizer in 2007 due to poor sales as it was found that though inhaled insulin appears to be as effective, but no better than injected short-acting insulin, the additional cost was so much more that was unlikely to be cost-effective.
At the time of Exubera's discontinuation, several other companies were pursuing inhaled insulininsulin. Afrezza which belongs to Mankind pharma received FDA approval in June 2014