This is because the effect described below, of forming microprecipitates below the skin, cannot happen
in the blood stream. All the
insulin in the blood is available immediately to the body.
Quote from above web page:
"
Pharmacodynamics:
Insulin glargine is a human insulin analog that has been designed to have low aqueous solubility at neutral pH. At pH 4, as in the LANTUS injection solution, it is completely soluble.