When should insulin therapy be initiated in type 2 diabetes?

Abstract

Insulin therapy in individuals with type 2 diabetes mellitus (T2DM) is indicated in several clinical settings. It may be initiated to achieve and maintain glycemic targets when disease progression exceeds the effectiveness of lifestyle interventions and non-insulin antihyperglycemic agents. Insulin is also an appropriate therapeutic option in patients with advanced chronic kidney disease, hepatic insufficiency, or heart failure. In addition, it is recommended as initial therapy in cases of marked hyperglycemia, defined by HbA1c ≥10%, blood glucose levels ≥300 mg/dL, or the presence of catabolic symptoms such as unintentional weight loss, polyuria, and polydipsia. Temporary insulin treatment may also be required during hospitalization, surgery, acute illness, high-dose glucocorticoid therapy, or pregnancy^1-3.

Basal insulin (BI), either neutral protamine Hagedorn (NPH) or a long-acting insulin analogue, is the preferred initial regimen. Sulfonylureas and meglitinides should generally be discontinued when insulin therapy is started, and the combination of insulin with thiazolidinediones is not recommended because of the increased risk of fluid retention and weight gain¹.

The starting dose of BI should be individualized according to the degree of hyperglycemia. In most patients, treatment can be initiated with 10 units/day or 0.1–0.2 units/kg/day. For individuals with HbA1c >8%, an initial dose of 0.2–0.3 units/kg/day may be considered. Dose titration should be performed every 3–5 days to achieve fasting plasma glucose targets of 80–130 mg/dL. If fasting glucose remains >130 mg/dL on 3–5 consecutive measurements without hypoglycemia, the BI dose should be increased by 2 units. If fasting glucose is consistently >180 mg/dL, an increase of 4 units may be appropriate. In the presence of hypoglycemia or fasting glucose <70 mg/dL, the dose should be reduced by 4 units^1-3.

If glycemic goals are not achieved after approximately 3 months of optimized BI therapy, postprandial hyperglycemia should be assessed through self-monitoring of blood glucose. In such cases, prandial insulin may be added, starting with 2–4 units (or 10% of the basal dose) before the meal associated with postprandial glucose levels >180 mg/dL. Dose adjustments of 1–2 units every 3–5 days are recommended based on glucose monitoring results1-3. Overbasalization should be avoided and is generally defined as BI doses >0.5 units/kg/day or >60 units/day^1-3.

BI may also be combined with glucagon-like peptide-1 receptor agonists (GLP-1 RAs) to improve glycemic control while minimizing weight gain and hypoglycemia risk^1-3.