What are the different types of insulin, their dosing regimens, and how should they be used for diabetes management?

Insulin Knowledge: Types, Regimens, and Clinical Use

For type 2 diabetes requiring insulin, start with basal insulin at 10 units daily or 0.1-0.2 units/kg/day, titrating by 2 units every 3 days until fasting glucose reaches target, then add prandial insulin if A1C remains above goal despite optimized basal dosing. 1

Insulin Types and Their Characteristics

Basal Insulins

• Long-acting analogs: Provide 24-hour coverage with reduced hypoglycemia risk compared to NPH
• NPH (intermediate-acting): Cheaper alternative but requires twice-daily dosing and carries higher hypoglycemia risk
• Choice depends on cost considerations and hypoglycemia risk 1

Prandial Insulins

Multiple options exist with progressively faster onset 2:

• Human regular insulin: Slowest onset, longest duration—risks post-meal hyperglycemia and delayed hypoglycemia
• Rapid-acting analogs (lispro, aspart, glulisine): Faster absorption, better meal-time coverage
• Ultra-rapid analogs (faster aspart, ultra-rapid lispro): Shortest onset, maximum meal flexibility
• Inhaled insulin (Technosphere): Alternative delivery route for prandial coverage

When to Start Insulin

Insulin is first-line when 1, 3:

• A1C >10% or glucose ≥300 mg/dL
• Symptomatic hyperglycemia (polyuria, polydipsia, weight loss)
• Type 1 diabetes is possible
• A1C ≥7.5% after optimizing other agents 4

Initiation Protocol for Type 2 Diabetes

Step 1: Basal Insulin Initiation

Start with 1:

• 10 units daily OR 0.1-0.2 units/kg/day
• Administer at bedtime (or morning if evening NPH causes hypoglycemia)
• Set individualized fasting plasma glucose target

Step 2: Basal Insulin Titration

• Increase by 2 units every 3 days until fasting glucose reaches goal without hypoglycemia 1
• For hypoglycemia: identify cause; if unclear, reduce dose by 10-20%
• Assess at every visit for signs of overbasalization (elevated bedtime-to-morning differential, postprandial spikes, hypoglycemia, high glucose variability)

Step 3: Intensification if A1C Remains Above Goal

Before adding prandial insulin, consider adding GLP-1 receptor agonist if not already prescribed—this combination reduces weight gain and insulin requirements 1, 4

If still above goal, add prandial insulin 1:

• Start with 4 units before largest meal OR 10% of basal dose
• Increase by 1-2 units or 10-15% based on postprandial glucose
• If on bedtime NPH, convert to twice-daily NPH plan

Step 4: Full Basal-Bolus Regimen

If A1C remains elevated 1:

• Basal insulin once daily PLUS
• Rapid-acting insulin before each meal
• Titrate each component individually based on corresponding glucose readings

Alternative Regimens

Premixed Insulin

• Twice-daily dosing: 2/3 before breakfast, 1/3 before dinner
• Reduces injection burden but less flexible
• Consider when adherence to multiple injections is challenging 1

Self-Mixed/Split Plans

• Allows separate adjustment of NPH and short/rapid-acting components
• Total NPH dose = 80% of current bedtime NPH
• Add 4 units short/rapid-acting to each injection 1

Critical Pitfalls to Avoid

Overbasalization: Pushing basal insulin doses higher when postprandial glucose is the problem—this causes hypoglycemia without improving A1C. Look for elevated bedtime-to-morning differentials as a signal to add prandial insulin instead 1

Abrupt discontinuation of oral agents: When starting insulin, continue metformin (reduces weight gain and insulin requirements) and other appropriate oral medications to prevent rebound hyperglycemia 4

Wrong needle length: Use 4-mm pen needles or 6-mm syringe needles as first-line—longer needles risk intramuscular injection, especially with long-acting insulins, causing severe hypoglycemia 4

Lipohypertrophy: Rotate injection sites properly; never inject into lipohypertrophic areas as this distorts absorption 4

Monitoring Strategy

• Titrate basal insulin using fasting glucose values
• Titrate prandial insulin using both fasting AND postprandial values 4
• Consider continuous glucose monitoring for patients on insulin—improves control 3
• Blood glucose monitoring is non-negotiable for safe insulin therapy 4

Special Considerations

Pregnancy: Use human regular insulin, aspart, lispro, or faster aspart—these are recommended options 2

Hypoglycemia management: Prescribe glucagon for all patients starting basal insulin 1

Cost: Basal insulin choice should factor in affordability; NPH is cheaper but requires more frequent dosing and monitoring 1