Which of the following is NOT a route for regular insulin formulations?

• A. Subcutaneous
• B. Intravenous
• C. Oral inhalation
• D. Topical

Answer: (D)

Insulin must reach the bloodstream in a way that preserves the protein’s structure and provides predictable absorption. Regular insulin is given most reliably by subcutaneous injection, and in hospital settings it can be given by intravenous infusion for rapid control. There is also an inhaled insulin option that delivers insulin through the lungs, bypassing the GI tract. The skin does not serve as a practical route for insulin because it is a strong barrier, and insulin is a large peptide that is poorly absorbed through topical application and would be degraded, making topical delivery ineffective. So topical administration is not used for regular insulin formulations.