What type of insulin is recommended for initial therapy?

Basal Insulin is the Recommended Type for Initial Insulin Therapy

For initial insulin therapy in type 2 diabetes, basal insulin (long-acting insulin analogs such as glargine, detemir, or degludec) is the recommended first-line insulin regimen. 1, 2

Why Basal Insulin First

Basal insulin alone is the most convenient and physiologically appropriate initial insulin treatment for type 2 diabetes because it specifically addresses the primary defect: excessive hepatic glucose production overnight and between meals 1. This approach allows you to:

• Start with a single daily injection at any time of day (though consistency matters), making it easier for patients to accept and adhere to therapy 1, 2
• Continue metformin and potentially one additional non-insulin agent, which provides complementary glucose-lowering mechanisms and reduces total insulin requirements 1, 2
• Titrate systematically based on fasting glucose values, which is straightforward for both clinicians and patients 1, 3

Specific Basal Insulin Options

Long-acting insulin analogs (glargine U-100, detemir, or degludec) are preferred over NPH insulin because they reduce nocturnal hypoglycemia risk by 22-58% while providing equivalent glycemic control 1, 4. The ultra-long-acting analogs (glargine U-300 or degludec) further reduce nocturnal hypoglycemia compared to glargine U-100 1.

Initial Dosing Algorithm

Start with 10 units once daily OR 0.1-0.2 units/kg/day, depending on the degree of hyperglycemia 1, 3, 2, 5:

• For mild-moderate hyperglycemia (A1C <9%): 10 units once daily is appropriate 3, 2
• For more severe hyperglycemia (A1C ≥9%): Use 0.2 units/kg/day as the starting dose 5
• For very severe hyperglycemia (A1C ≥10-12% with symptoms): Consider starting with 0.3-0.5 units/kg/day as total daily dose, split between basal and prandial insulin immediately 3, 2

Titration Protocol

Increase basal insulin by 2-4 units every 3 days until fasting glucose reaches 80-130 mg/dL 1, 3, 2:

• If fasting glucose is 140-179 mg/dL: increase by 2 units every 3 days 3
• If fasting glucose is ≥180 mg/dL: increase by 4 units every 3 days 3
• If hypoglycemia occurs: reduce dose by 10-20% immediately 1, 3

Equip patients with self-titration algorithms based on home glucose monitoring to accelerate achievement of glycemic targets 3, 2.

Critical Threshold: When to Stop Escalating Basal Insulin

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, STOP escalating and add prandial insulin instead 1, 3. Continuing to increase basal insulin beyond this threshold leads to "overbasalization"—a dangerous pattern characterized by:

• Bedtime-to-morning glucose differential ≥50 mg/dL 1, 3
• Increased hypoglycemia risk 1, 3
• High glucose variability 1, 3
• Suboptimal A1C control despite high basal doses 3

When Basal-Only Insulin is Insufficient

Add prandial insulin when 1, 3, 2:

• Fasting glucose is controlled (80-130 mg/dL) but A1C remains above target after 3-6 months of basal insulin optimization
• Basal insulin dose approaches 0.5-1.0 units/kg/day without achieving A1C goal
• Significant postprandial glucose excursions persist despite adequate fasting control

Start with 4 units of rapid-acting insulin before the largest meal OR 10% of the current basal dose, then titrate by 1-2 units every 3 days based on postprandial readings 1, 3.

Alternative to prandial insulin: Consider adding a GLP-1 receptor agonist (or using a fixed-ratio combination product like iGlarLixi or IDegLira) to address postprandial hyperglycemia while minimizing weight gain and hypoglycemia risk 1, 2.

Exception: When to Start with Basal-Bolus Immediately

Start with both basal AND prandial insulin from the outset when 1, 2:

• Blood glucose ≥300-350 mg/dL AND/OR A1C 10-12% with symptomatic or catabolic features (weight loss, polyuria, polydipsia)
• Type 1 diabetes is suspected (use approximately one-third of total daily insulin as basal, two-thirds as prandial) 5
• Evidence of ongoing catabolism is present 1

In these severe cases, basal-only insulin will be insufficient to achieve rapid glycemic control and prevent metabolic decompensation 3, 6.

Common Pitfalls to Avoid

• Delaying insulin initiation in patients not achieving glycemic goals with oral medications prolongs exposure to hyperglycemia and increases complication risk 3, 2
• Continuing to escalate basal insulin beyond 0.5-1.0 units/kg/day without adding prandial coverage leads to overbasalization with increased hypoglycemia and suboptimal control 1, 3
• Discontinuing metformin when starting insulin—metformin should be continued unless contraindicated, as it reduces total insulin requirements 1, 2
• Using sliding scale insulin alone without scheduled basal insulin is ineffective for long-term glycemic management 3, 6

Administration Details

• Inject subcutaneously into the abdomen, thigh, or deltoid at the same time each day 5
• Rotate injection sites within the same region to reduce lipodystrophy risk 5
• Do NOT mix or dilute insulin glargine with any other insulin or solution 5
• Do NOT administer intravenously or via insulin pump 5