What is the recommended approach for initiating insulin therapy in a patient with a history of impaired glucose regulation and potential comorbidities such as impaired renal function or previous hypoglycemia?

How to Start Insulin Therapy

For most patients with type 2 diabetes requiring insulin, start with basal insulin at 10 units once daily (or 0.1-0.2 units/kg body weight), continue metformin unless contraindicated, and titrate by 2-4 units every 3 days until fasting glucose reaches 80-130 mg/dL. 1, 2

When to Initiate Insulin

Insulin should be started immediately in the following situations:

• Severe hyperglycemia: Blood glucose ≥300 mg/dL or A1C ≥10% 1
• Symptomatic hyperglycemia: Polyuria, polydipsia, weight loss, or other catabolic features 1
• Ketosis or ketoacidosis: Requires immediate insulin regardless of glucose level 1
• Inadequate control on oral agents: A1C remains >7% despite optimal oral medications 1

For youth with type 2 diabetes, start insulin when blood glucose ≥250 mg/dL with A1C ≥8.5% without acidosis 1, 3

Initial Dosing Strategy

Type 2 Diabetes - Standard Approach

Start with basal insulin only for most patients with mild-to-moderate hyperglycemia (A1C <9%):

• Dose: 10 units once daily OR 0.1-0.2 units/kg body weight 1, 2
• Timing: Same time each day, typically at bedtime 1, 2
• Continue metformin at maximum tolerated dose (up to 2000-2550 mg daily) unless contraindicated 1, 2

Type 2 Diabetes - Severe Hyperglycemia

For patients with A1C ≥10% or blood glucose ≥300-350 mg/dL with symptoms:

• Start basal-bolus regimen immediately with total daily dose of 0.3-0.5 units/kg 1, 2
• Split 50% as basal insulin once daily 1, 2
• Split 50% as prandial insulin divided among three meals 1, 2

Type 1 Diabetes

• Total daily dose: 0.4-1.0 units/kg/day, typically 0.5 units/kg/day for metabolically stable patients 1, 2
• Split 40-60% as basal insulin once daily 2
• Split 40-60% as prandial insulin divided among meals 2

Youth with Type 2 Diabetes

For marked hyperglycemia (glucose ≥250 mg/dL, A1C ≥8.5%) without ketoacidosis:

• Start basal insulin at 0.5 units/kg/day while simultaneously initiating metformin 1, 3
• Metformin: Start 500 mg twice daily, increase to 1000 mg twice daily over 2-4 weeks 3

Titration Algorithm

Basal Insulin Adjustment

Adjust dose every 3 days based on fasting glucose patterns 1, 2:

• If fasting glucose 140-179 mg/dL: Increase by 2 units 1
• If fasting glucose ≥180 mg/dL: Increase by 4 units 1
• Target: Fasting glucose 80-130 mg/dL 1
• If hypoglycemia occurs: Reduce dose by 10-20% immediately 1, 2

Empower patients with self-titration algorithms based on home glucose monitoring to improve control 1, 2

Critical Threshold: When to Add Prandial Insulin

Stop escalating basal insulin when the dose exceeds 0.5 units/kg/day and instead add prandial coverage 1, 2:

Signs of "Overbasalization"

• Basal dose >0.5 units/kg/day 1, 2
• Bedtime-to-morning glucose differential ≥50 mg/dL 1, 2
• Hypoglycemia episodes 1, 2
• High glucose variability 1, 2

Adding Prandial Insulin

When basal insulin is optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months 1:

• Start with 4 units of rapid-acting insulin before the largest meal OR 10% of basal dose 1, 2
• Titrate by 1-2 units every 3 days based on 2-hour postprandial glucose 1, 2
• Add to additional meals as needed based on glucose patterns 1

Special Populations

Elderly or Renal Impairment

For patients >65 years, eGFR <45 mL/min/1.73 m², or poor oral intake:

• Use lower starting doses: 0.1-0.25 units/kg/day 2, 4
• Monitor more frequently for hypoglycemia 1, 5
• Reduce total daily dose by 50% for CKD Stage 5 with type 2 diabetes 2

Hospitalized Patients

For non-critically ill hospitalized patients:

• Insulin-naive or low-dose: Start 0.3-0.5 units/kg/day total, split 50% basal and 50% bolus 1, 2
• High-dose home insulin (≥0.6 units/kg/day): Reduce by 20% upon admission 1, 2
• Poor oral intake: Use basal insulin with correction doses only, avoid prandial insulin 1

Administration Guidelines

Injection Technique

• Basal insulin: Inject subcutaneously in abdomen, thigh, buttocks, or upper arm 2, 5
• Prandial insulin: Administer 0-15 minutes before meals 1, 5, 6
• Rotate injection sites within same region to prevent lipodystrophy 5, 6
• Use shortest needles (4-mm pen or 6-mm syringe) as first-line choice 6

Insulin Selection

• Basal options: Insulin glargine, detemir, or NPH 1, 2
• Prandial options: Rapid-acting analogues (lispro, aspart, glulisine) preferred over regular insulin 1, 5
• Cost considerations: NPH may be more affordable despite slightly higher hypoglycemia risk 1

Common Pitfalls to Avoid

Critical Errors

• Never delay insulin initiation in patients not achieving goals with oral medications—this prolongs hyperglycemia exposure 1, 2
• Never discontinue metformin when starting insulin unless contraindicated—combination provides superior control with less weight gain 1, 2
• Never use sliding scale insulin as monotherapy—it treats hyperglycemia reactively rather than preventing it 1
• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without adding prandial coverage—this causes overbasalization 1, 2

Medication Interactions

Drugs increasing hypoglycemia risk: ACE inhibitors, fibrates, fluoxetine, MAO inhibitors, salicylates, sulfonamides 5

Drugs decreasing insulin effect: Corticosteroids, thiazides, thyroid hormones, atypical antipsychotics 5

Monitoring Requirements

During Titration

• Daily fasting glucose monitoring essential during active titration 1, 2
• Check A1C every 3 months during intensive adjustment 1, 3
• Assess for hypoglycemia at every visit 1, 2

Patient Education Essentials

Provide comprehensive education on 1, 2:

• Injection technique and site rotation
• Glucose monitoring and target ranges
• Hypoglycemia recognition and treatment (15 grams fast-acting carbohydrate for glucose ≤70 mg/dL)
• Sick day management rules
• Insulin storage and handling

Alternative to Prandial Insulin

Consider adding a GLP-1 receptor agonist instead of prandial insulin when basal insulin alone is insufficient 1:

• Provides comparable A1C reduction with lower hypoglycemia risk 1
• Causes weight loss rather than weight gain 1
• Preferred injectable medication before advancing to basal-bolus regimen 1