What characteristic of glargine makes it a long-acting insulin?

The characteristic that makes glargine a long-acting insulin is its ability to form crystals in subcutaneous tissue. When glargine is injected, it precipitates in the neutral pH of subcutaneous tissue, leading to a slow and prolonged release of insulin into the bloodstream. This slow release mechanism results in a steady concentration of insulin that can last for up to 24 hours or more, providing a consistent basal level of insulin and minimizing fluctuations in blood glucose levels.

The other options do not contribute to the long-acting nature of glargine. Rapid absorption into blood circulation would typically be associated with shorter-acting insulins, leading to peaks in insulin levels rather than a steady state. While an increase in peripheral insulin sensitivity is an important aspect of how insulin functions in the body, it does not describe glargine's pharmacokinetics. Binding to plasma proteins can influence the bioavailability of drugs, but in the case of glargine, its prolonged action is primarily due to its crystallization and gradual dissolution over time, rather than its interaction with plasma proteins.