What type of insulin should be prescribed to a patient with diabetes?

How to Decide What Type of Insulin to Prescribe

Start with basal insulin (glargine, detemir, degludec, or NPH) at 0.1-0.2 units/kg/day or 10 units once daily, combined with metformin, as the initial insulin regimen for patients with type 2 diabetes not achieving glycemic goals on oral agents. 1, 2

Initial Insulin Selection Algorithm

Step 1: Assess Clinical Severity

• If HbA1c ≥10-12% with symptoms, ketosis, or unintentional weight loss: Start basal-bolus insulin immediately (basal insulin plus rapid-acting insulin before meals), not just basal insulin alone 1
• If HbA1c 9-10%: Consider starting basal insulin, but be prepared to advance quickly 1
• If HbA1c 7.5-9%: Start with basal insulin once daily 1, 3

Step 2: Choose the Basal Insulin Type

Long-acting analogues (glargine, detemir, degludec) are preferred over NPH insulin because they cause less nocturnal hypoglycemia and have more predictable pharmacokinetics 1, 4, 5

However, consider NPH insulin if:

• Cost is a major barrier (NPH is significantly less expensive) 1
• Patient is on corticosteroids (NPH given in morning matches steroid-induced daytime hyperglycemia pattern) 2

Specific basal insulin characteristics:

• Glargine and detemir: Modestly less overnight hypoglycemia than NPH 1
• Detemir: May cause slightly less weight gain than NPH or glargine 1, 4
• Degludec: Longer duration of action, may allow more flexible dosing 1

Step 3: Initial Dosing Strategy

• Standard dose: 0.1-0.2 units/kg/day or 10 units once daily 1, 2
• For elderly or renal insufficiency: Use lower end (0.1 units/kg/day) to minimize hypoglycemia risk 2
• Continue metformin and possibly one additional oral agent 1, 2

Step 4: Titration Protocol

Increase basal insulin by 2 units every 3 days until fasting glucose reaches 100-130 mg/dL without hypoglycemia 2, 6

• If hypoglycemia occurs without clear cause, reduce dose by 10-20% 2
• Equip patients with self-titration algorithms based on self-monitoring of blood glucose 2

When Basal Insulin Alone Is Insufficient

Criteria for Advancing Therapy

If basal insulin is optimally titrated (fasting glucose at target) but HbA1c remains above goal, or if basal dose exceeds 0.5 units/kg/day without achieving targets, advance to combination injectable therapy 1, 6

Step 5: Add Prandial Coverage - Three Options

Option A: Add GLP-1 receptor agonist (preferred if weight gain or hypoglycemia are concerns) 1

Option B: Add rapid-acting insulin before largest meal ("basal-plus" strategy):

• Start with 4 units before the meal with greatest postprandial glucose excursion, or 10% of basal dose 1, 2, 7
• Reduce basal insulin by same amount (4 units or 10%) 2
• Use rapid-acting analogues (lispro, aspart, glulisine) rather than regular insulin for better postprandial control 1
• If still inadequate, add rapid-acting insulin before additional meals sequentially 7

Option C: Switch to premixed insulin (70/30 NPH/regular, 70/30 aspart mix, or 75/25 or 50/50 lispro mix) twice daily:

• Requires fixed meal schedule and carbohydrate content 1
• Less flexible but simpler dosing 1, 3
• Suboptimal for covering postprandial excursions compared to basal-bolus 1

Step 6: Full Basal-Bolus Regimen

If multiple prandial doses are needed, transition to full basal-bolus therapy:

• Continue basal insulin (typically 50% of total daily dose) 6
• Add rapid-acting insulin before each meal (distribute remaining 50% across meals based on carbohydrate content: 30-40% per meal) 6
• Discontinue sulfonylureas, DPP-4 inhibitors, and GLP-1 agonists when using complex insulin regimens 1
• May continue metformin (reduces weight gain and insulin requirements) 3
• Consider continuing SGLT-2 inhibitors or thiazolidinediones to reduce total insulin dose, but monitor for side effects (heart failure with thiazolidinediones, ketoacidosis with SGLT-2 inhibitors) 1

Special Considerations

Type 1 Diabetes

• Always start with basal-bolus therapy at diagnosis (multiple daily injections of rapid-acting insulin before meals plus basal insulin) 3
• Premixed insulin twice daily is an alternative but less optimal 3
• More complex intensive strategies are required compared to type 2 diabetes 1

Concentrated Insulin Products

Consider for patients requiring >200 units/day:

• U-500 regular insulin (has both basal and prandial properties) 1
• U-300 glargine or U-200 degludec (longer duration, higher basal doses per volume) 1
• U-200 lispro (less volume for large prandial doses) 1

Inhaled Insulin

• Available for prandial use with limited dosing range 1
• Contraindicated in chronic lung disease (asthma, COPD) and smokers 1
• Requires spirometry before and after initiation 1

Critical Pitfalls to Avoid

• Do not delay insulin initiation in patients not achieving glycemic targets with oral agents 1, 2
• Do not use sliding scale insulin alone as primary therapy, especially in type 1 diabetes 2
• Do not abruptly discontinue oral medications when starting insulin (risk of rebound hyperglycemia) 3
• Avoid injecting into lipohypertrophy sites (distorts absorption); rotate injection sites properly 3
• Do not use only fasting glucose to guide therapy once prandial insulin is added; monitor pre-meal and bedtime glucose 2, 3
• Watch for over-basalization: elevated bedtime-to-morning glucose differential, hypoglycemia, or high glucose variability signal need for prandial insulin rather than more basal insulin 2