What are the dosing recommendations for rapid-acting (e.g. insulin aspart, insulin lispro), short-acting, intermediate-acting, and long-acting (e.g. insulin glargine, insulin detemir) insulins in type 1 and type 2 diabetes, and how are they adjusted based on blood glucose monitoring results?

Insulin Dosing and Adjustment in Type 1 and Type 2 Diabetes

Type 1 Diabetes: Initial Dosing

For Type 1 diabetes, start with a total daily dose of 0.5 units/kg/day, dividing this as 40-50% basal insulin (long-acting) and 50-60% prandial insulin (rapid-acting) distributed across meals. 1, 2

Basal Insulin Component

• Administer long-acting insulin analogs (glargine, detemir, or degludec) once daily at the same time each day 1
• Glargine U-100 and detemir typically provide 24-hour coverage with once-daily dosing, though detemir may require twice-daily administration in some patients 1
• For a metabolically stable 70 kg patient: Total daily dose = 35 units (0.5 × 70), with approximately 17-18 units as basal insulin 2

Prandial Insulin Component

• Use rapid-acting insulin analogs (aspart, lispro, or glulisine) administered 0-15 minutes before each meal 1, 3, 4
• Distribute the remaining 50-60% of total daily dose across three meals based on carbohydrate content 1
• Rapid-acting analogs provide superior postprandial control compared to regular insulin, with peak action at 1-2 hours and duration of 3-4 hours 1, 5

Special Considerations for Type 1

• Patients presenting with diabetic ketoacidosis require higher initial doses immediately following presentation 2
• During the "honeymoon phase" with residual beta-cell function, doses as low as 0.2-0.6 units/kg/day may suffice 2
• Adolescents during puberty often require doses exceeding 1.0 units/kg/day 2

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Type 2 Diabetes: Initial Dosing

For insulin-naive Type 2 diabetes patients, initiate basal insulin at 10 units once daily or 0.1-0.2 units/kg/day, administered at the same time each day. 1, 2

Starting Strategy

• Continue metformin unless contraindicated when adding basal insulin 1
• For patients with severe hyperglycemia (A1C ≥9%, glucose ≥300-350 mg/dL), consider higher starting doses of 0.3-0.4 units/kg/day 1, 2
• Patients with A1C 10-12% with symptomatic or catabolic features require immediate basal-bolus insulin therapy rather than basal insulin alone 2

Basal Insulin Selection

• Long-acting analogs (glargine U-100, detemir, degludec) demonstrate lower nocturnal hypoglycemia risk compared to NPH insulin 1, 6
• Glargine provides peakless insulin coverage over 24 hours with onset at 1 hour 6
• Administer at any consistent time of day, though bedtime dosing is common 6

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Insulin Dose Titration Algorithms

Basal Insulin Titration for Type 2 Diabetes

Increase basal insulin by 2 units every 3 days if fasting glucose is 140-179 mg/dL, or by 4 units every 3 days if fasting glucose ≥180 mg/dL, until reaching target of 80-130 mg/dL. 1, 2

Systematic Titration Protocol

• Monitor fasting blood glucose daily during titration phase 1, 2
• If ≥2 fasting glucose values per week are <80 mg/dL, decrease dose by 2 units 2
• If hypoglycemia occurs, reduce dose by 10-20% immediately and investigate the cause 2
• Alternative approach: Increase by 10-15% of current dose once or twice weekly 1, 2

Critical Threshold: Recognizing Overbasalization

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, add prandial insulin rather than continuing to escalate basal insulin alone. 1, 2

Clinical signals indicating overbasalization include: 1, 2

• Basal dose >0.5 units/kg/day
• Bedtime-to-morning glucose differential ≥50 mg/dL
• Hypoglycemia (aware or unaware)
• High glucose variability
• Controlled fasting glucose but elevated A1C

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Adding Prandial Insulin

Indications for Prandial Insulin Addition

Add prandial insulin when basal insulin has been optimized (fasting glucose 80-130 mg/dL) but A1C remains above target after 3-6 months, or when basal insulin approaches 0.5-1.0 units/kg/day without achieving glycemic goals. 1, 2

Prandial Insulin Initiation

• Start with 4 units of rapid-acting insulin before the largest meal, or use 10% of current basal insulin dose 1, 2
• Add prandial insulin to the meal causing the greatest postprandial glucose excursion first 2
• Titrate by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings 2

Prandial Insulin Characteristics

• Rapid-acting analogs (aspart, lispro, glulisine) must be administered 0-15 minutes before meals 1, 3, 4
• Regular human insulin requires administration 15-30 minutes before meals with peak at 3-4 hours and duration of 6-8 hours 1
• Rapid-acting analogs provide better postprandial control and lower late hypoglycemia risk compared to regular insulin 7, 5

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Intermediate-Acting Insulin (NPH)

NPH Characteristics and Limitations

• Onset at 1 hour, peak at 6-8 hours, duration of 12 hours 1
• NPH is inappropriate for continuous basal coverage in Type 1 diabetes due to pronounced peak, short duration, and high variability 7
• When used, requires twice-daily dosing with fixed meal timing to avoid hypoglycemia during peak action 1

NPH in Combination Regimens

• Can be mixed with rapid-acting analogs in the same syringe for Type 1 diabetes, with typical ratios of 70/30 at breakfast, 60/40 at lunch, and 80/20 at supper (lispro/NPH percentages) 8
• When switching from twice-daily NPH to once-daily long-acting analog, start with 80% of total NPH dose 9
• When switching from once-daily NPH to glargine, use the same dose 9

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Combining Insulin Types: Practical Regimens

Multiple Daily Injections (MDI) for Type 1 Diabetes

The optimal regimen uses long-acting analog once daily (50% of total daily dose) plus rapid-acting analog before each meal (50% divided among meals). 1

Advantages of MDI with Analogs

• Flexibility in meal timing and content 1
• Can adjust individual meal doses based on carbohydrate intake using insulin-to-carbohydrate ratios 1
• Lower hypoglycemia risk compared to NPH-based regimens 1

Adjustment Parameters for MDI

• Mealtime insulin: If carbohydrate counting is accurate, change insulin-to-carbohydrate ratio if glucose after meals consistently out of target 1
• Correction insulin: Adjust insulin sensitivity factor if correction doses don't consistently bring glucose into range 1
• Basal insulin: Adjust based on overnight, fasting, or daytime glucose outside the activity window of rapid-acting boluses 1

Twice-Daily Split-Mixed Regimen (Less Preferred)

This older regimen uses NPH plus regular insulin twice daily: 1

• Pre-breakfast: 40% NPH + regular insulin
• Pre-dinner: 30% NPH + regular insulin
• Major disadvantages: Fixed meal timing required, difficult to reach targets without hypoglycemia, afternoon and nocturnal hypoglycemia risk from NPH peaks 1

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Insulin Pump Therapy (Continuous Subcutaneous Insulin Infusion)

Pump Dosing Strategy

• Basal delivery of rapid-acting analog comprises 40-60% of total daily dose 1
• Remaining 40-60% delivered as meal and correction boluses 1
• Can adjust basal rates hourly for varying insulin sensitivity throughout the day 1

Pump Advantages

• Most physiologic insulin replacement currently available 7, 10
• Flexibility for exercise, sick days, and varying schedules 1
• Lower glucose variability compared to injection-based regimens 1

Pump-Specific Considerations

• Change insulin reservoir at least every 7 days 3
• Do not dilute or mix insulins in pump reservoir 3
• Do not expose pump insulin to temperatures >98.6°F (37°C) 3
• Patients must have backup injection insulin available for pump failures 1

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Special Clinical Situations

Hospitalized Patients

• For insulin-naive hospitalized patients, start with total daily dose of 0.3-0.5 units/kg, giving half as basal insulin 2
• For patients on high-dose home insulin (≥0.6 units/kg/day), reduce total daily dose by 20% upon hospitalization to prevent hypoglycemia 2
• High-risk patients (elderly >65 years, renal failure, poor oral intake) require lower doses of 0.1-0.25 units/kg/day 2

Patients on Corticosteroids

• For patients with diabetes on steroids, add 0.1-0.3 units/kg/day glargine to usual insulin regimen 2
• Dose determined by steroid dose and oral intake 2

Simplifying Complex Regimens in Older Adults

• Convert to basal-only insulin by using 70% of total daily dose as morning basal insulin 1
• Discontinue prandial insulin if ≤10 units per dose and add non-insulin agents 1
• Change timing from bedtime to morning administration 1
• Adjust every 2 weeks based on pre-meal glucose monitoring 1

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Critical Pitfalls to Avoid

Common Dosing Errors

• Never delay insulin initiation in Type 2 diabetes patients not achieving glycemic goals with oral medications 2
• Do not continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia 2
• Avoid relying solely on correction insulin without scheduled basal and prandial components 2
• Never mix or dilute glargine with other insulins due to its low pH 2, 9

Administration Errors

• Rotate injection sites within the same region to prevent lipodystrophy and localized cutaneous amyloidosis 9, 3
• Do not inject into areas of lipodystrophy, as this causes erratic absorption and hyperglycemia 9, 3
• Never share insulin pens, cartridges, or needles between patients 9, 3

Monitoring Failures

• Increase frequency of blood glucose monitoring during any insulin regimen changes 9, 3
• Do not adjust insulin doses without appropriate glucose monitoring 9
• Assess for overbasalization at every clinical visit 2

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Ongoing Adjustment Principles

When to Intensify Therapy

• If A1C remains above target after 3-6 months of optimized basal insulin (fasting glucose 80-130 mg/dL), add prandial insulin or GLP-1 receptor agonist 1, 2
• Consider combination injectable therapy (basal insulin + GLP-1 RA) to minimize weight gain and hypoglycemia risk 1

Dose Modification Factors

• Adjust doses with changes in physical activity, meal patterns, acute illness, or renal/hepatic function 9, 3
• All dosage adjustments should occur under medical supervision with appropriate glucose monitoring 9
• Patients can be taught self-titration using structured algorithms based on self-monitoring results 2

Hypoglycemia Management

• If hypoglycemia occurs, determine the cause and reduce the relevant insulin component by 10-20% 2
• If ≥2 glucose values per week are <80 mg/dL, decrease that insulin dose by 2 units 2
• Patients must be educated on recognition and treatment of hypoglycemia before intensive insulin therapy 1