How should I transition an adult with type 2 diabetes and elevated hemoglobin A1c, who has preserved renal function and is on metformin and other oral antidiabetic agents, to insulin therapy?

Transitioning from Oral Antidiabetics to Insulin in Type 2 Diabetes

For patients with type 2 diabetes on oral agents who require insulin, initiate basal insulin at 0.5 units/kg/day while continuing metformin at maximum tolerated dose (2000 mg daily), and discontinue sulfonylureas or glinides to minimize hypoglycemia risk. 1, 2

Assess Current Glycemic Control and Determine Urgency

Immediate insulin initiation is mandatory when:

• HbA1c ≥8.5% with symptoms (polyuria, polydipsia, weight loss) 3, 2
• Random blood glucose ≥250 mg/dL (13.9 mmol/L) 3
• HbA1c ≥10% regardless of symptoms 3, 4
• Presence of ketosis or ketoacidosis (requires IV insulin first, then transition to subcutaneous) 3, 2

For less severe hyperglycemia (HbA1c 8-9%), consider adding basal insulin while maintaining oral agents, with endocrinology consultation for treatment intensification. 3

Pre-Insulin Checklist

Before initiating insulin therapy, verify the following:

• Renal function: eGFR >30 mL/min/1.73 m² is required to continue metformin; eGFR >60 mL/min/1.73 m² is preferred 3, 2
• Rule out ketosis/ketoacidosis: Check urine ketones or serum beta-hydroxybutyrate; if present, IV insulin is required initially 3, 2
• Confirm type 2 diabetes: Exclude type 1 diabetes by assessing for autoantibodies if clinical presentation is atypical 3

Specific Insulin Initiation Protocol

Starting dose and titration:

• Begin basal insulin (glargine, detemir, or NPH) at 0.5 units/kg/day, administered once daily at bedtime 2, 5, 4
• Titrate upward by 2-4 units every 3 days based on fasting blood glucose, targeting fasting glucose 80-130 mg/dL 2
• Continue metformin 2000 mg daily throughout insulin therapy to reduce insulin requirements, minimize weight gain, and decrease hypoglycemia risk 4, 6

Management of other oral agents:

• Discontinue sulfonylureas and glinides immediately when starting insulin to avoid severe hypoglycemia 3
• Continue metformin unless contraindicated by renal function 3, 4, 6
• Consider continuing DPP-4 inhibitors, SGLT2 inhibitors, or GLP-1 receptor agonists as they complement insulin action without increasing hypoglycemia risk 3
• Thiazolidinediones may be continued but monitor for fluid retention and weight gain 3

Monitoring and Follow-Up

Blood glucose monitoring requirements:

• Check fasting blood glucose daily to guide basal insulin titration 2, 4
• Perform periodic pre-meal and bedtime glucose checks to assess overall control 2
• Measure HbA1c every 3 months until target <7% is achieved, then every 6 months 1, 2

Reassess at 3 months:

• If HbA1c remains >7% despite optimized basal insulin (fasting glucose 80-130 mg/dL), add prandial insulin before the largest meal, starting at 4 units or 10% of basal dose 3
• If multiple daily injections are needed, consider basal-bolus regimen with rapid-acting insulin analogs (lispro, aspart, or glulisine) before each meal 3, 4

Potential for Insulin De-escalation

Once glucose targets are achieved (HbA1c <7%), insulin can be tapered in select patients:

• Reduce basal insulin by 10-30% every few days over 2-6 weeks while maintaining metformin 3, 2
• This approach is appropriate when initial hyperglycemia was due to glucose toxicity rather than absolute insulin deficiency 3, 7
• Continue close monitoring with HbA1c checks every 3 months during and after tapering 1, 2

Critical Pitfalls to Avoid

Do not delay insulin when clearly indicated: Prolonged severe hyperglycemia increases complication risk and may worsen beta-cell function through glucose toxicity 2, 7

Do not abruptly discontinue all oral agents: Stopping metformin when starting insulin leads to rebound hyperglycemia, increased insulin requirements, and greater weight gain 4, 6

Do not continue sulfonylureas with insulin: This combination dramatically increases hypoglycemia risk without improving glycemic control 3

Do not use inadequate starting doses: Starting with <0.5 units/kg/day or failing to titrate aggressively prolongs poor control 2, 4

Patient Education Requirements

Provide comprehensive instruction on:

• Insulin injection technique using 4-mm pen needles (safest and least painful) 4
• Proper site rotation to prevent lipohypertrophy, which impairs insulin absorption 4
• Recognition and treatment of hypoglycemia (blood glucose <70 mg/dL: consume 15g fast-acting carbohydrate) 3, 4
• Sick day management rules (never stop basal insulin, check glucose more frequently) 4
• Insulin storage (unopened vials refrigerated; in-use vials at room temperature for up to 28 days) 4

Alternative to Insulin for Severe Hyperglycemia

If the patient refuses insulin despite HbA1c ≥9%, consider adding a GLP-1 receptor agonist (liraglutide, semaglutide, or dulaglutide) to maximum-dose metformin, though this approach is suboptimal and may be insufficient at very high HbA1c levels. 7, 8 GLP-1 receptor agonists can reduce HbA1c by 2-3% from baseline levels of 10-11% without causing hypoglycemia or weight gain, and may even produce superior HbA1c reduction compared to basal insulin in some patients 7. However, insulin remains the most reliable and effective option for severe hyperglycemia, particularly when HbA1c exceeds 10% 3, 4.