What is the recommended mealtime insulin lispro dose (units per kilogram and per meal) for an adult with type 1 diabetes, and how is the correction dose calculated?

Insulin Lispro Dosing in Type 1 Diabetes

For adults with type 1 diabetes, insulin lispro is dosed at approximately 0.25–0.3 units/kg/day divided among three meals (roughly 50–60% of total daily insulin), with each meal dose calculated using a carbohydrate-to-insulin ratio (typically 1 unit per 10–15 grams of carbohydrate) plus correction insulin based on an individualized insulin sensitivity factor.

Total Daily Insulin Requirements

• Adults with type 1 diabetes require 0.4–1.0 units/kg/day as total daily insulin, with 0.5 units/kg/day being the standard starting point for metabolically stable patients 1.
• Approximately 50–60% of the total daily dose is allocated to prandial (mealtime) insulin, while 40–50% is given as basal insulin 1, 2.
• Higher doses are required during puberty (up to 1.5 units/kg/day), pregnancy, and acute illness 1, 3.

Mealtime Lispro Dosing

Initial Dose Calculation

• For a 70 kg adult on 0.5 units/kg/day (35 units total), allocate ≈18–21 units as prandial insulin divided across three meals, yielding ≈6–7 units per meal 1, 2.
• When transitioning from regular insulin to lispro, reduce the short-acting component by approximately 30% and increase NPH by a similar amount to maintain glycemic control 4.

Carbohydrate-to-Insulin Ratio (CIR)

• Calculate the CIR using the formula: 450 ÷ total daily insulin dose 2.
• For a patient on 35 units/day: 450 ÷ 35 = ≈13 grams of carbohydrate per 1 unit of insulin 2.
• A common starting ratio is 1 unit per 10–15 grams of carbohydrate, which can be individualized based on post-prandial glucose responses 2, 5.
• The CIR often varies throughout the day—patients typically require more insulin per gram of carbohydrate at breakfast due to counter-regulatory hormones (cortisol, growth hormone) 1.

Correction (Supplemental) Insulin

Insulin Sensitivity Factor (ISF)

• Calculate the ISF using: 1500 ÷ total daily insulin dose (for regular insulin) or 1700 ÷ total daily insulin dose (for rapid-acting analogs) 2.
• For a patient on 35 units/day: 1700 ÷ 35 = ≈49 mg/dL drop per 1 unit of insulin 2.
• The correction dose is: (Current glucose – Target glucose) ÷ ISF 2.

Simplified Correction Protocol

• Add 2 units of lispro for pre-meal glucose >250 mg/dL 2.
• Add 4 units for pre-meal glucose >350 mg/dL 2.
• These correction units are in addition to the carbohydrate-coverage dose 2.

Timing of Administration

• Administer lispro 0–15 minutes before meals—ideally immediately before eating—for optimal post-prandial glucose control 1, 2.
• Lispro has an onset of 0.25–0.5 hours, peak at 1–3 hours, and duration of 3–5 hours 2.
• Never give lispro at bedtime as a sole correction dose, as this markedly increases nocturnal hypoglycemia risk 1, 2.

Dose Titration

• Adjust each meal dose by 1–2 units (≈10–15%) every 3 days based on the 2-hour post-prandial glucose reading 1, 2.
• Target post-prandial glucose <180 mg/dL 1, 2.
• If unexplained hypoglycemia (<70 mg/dL) occurs, reduce the implicated dose by 10–20% immediately 1, 2.

Monitoring Requirements

• Check fasting glucose daily to guide basal insulin adjustments 1, 2.
• Measure pre-meal glucose immediately before each meal to calculate correction doses 2.
• Obtain 2-hour post-prandial glucose after each meal to assess prandial adequacy and guide titration 2.
• Reassess HbA1c every 3 months during intensive titration 2.

Combination with Basal Insulin

• Basal insulin (glargine, detemir, or degludec) provides the remaining 40–50% of total daily insulin as once- or twice-daily injections 1, 2.
• When using NPH as basal insulin, it can be mixed with lispro at breakfast, lunch, and dinner in approximate ratios of 70/30,60/40, and 80/20 (lispro/NPH) to optimize pre-meal and bedtime glucose 4.
• With long-acting analogs (glargine, detemir), do not mix with lispro—administer as separate injections 3.

Special Situations

Pump Therapy

• In insulin pump therapy, the basal rate accounts for approximately 40–60% of total daily insulin, with the remainder as mealtime and correction boluses 2.
• The pump's on-board calculator uses pre-programmed CIR and ISF to calculate bolus doses, accounting for "insulin on board" to prevent dose stacking 1.

Variable Meal Timing or Content

• Lispro's rapid onset allows flexible meal timing—patients can inject immediately before eating without the 30–45 minute wait required for regular insulin 4, 5.
• The dose can be adjusted based on actual carbohydrate content of the meal using the CIR 1, 5.

Exercise

• Reduce the lispro dose by 10–20% before anticipated moderate-to-vigorous exercise to prevent hypoglycemia 2.

Clinical Outcomes

• Long-term intensive therapy with lispro + NPH achieves lower mean daily glucose (8.0 vs. 8.8 mmol/L) and lower HbA1c (6.34% vs. 6.71%) compared with regular insulin 4.
• Lispro results in less frequent hypoglycemia (7.4 vs. 11.5 episodes/patient-month) and improved hypoglycemia awareness compared with regular insulin 4.
• When combined with glargine, lispro achieves better glycemic control with fewer hypoglycemic episodes than NPH-based regimens 6.

Common Pitfalls to Avoid

• Do not use sliding-scale insulin as monotherapy in type 1 diabetes—this can precipitate diabetic ketoacidosis 1, 2.
• Do not delay insulin initiation or prescribe inadequate doses—immediate basal-bolus therapy is required for type 1 diabetes 2.
• Do not rely solely on correction doses without adjusting scheduled basal and prandial insulin 2.
• Do not administer lispro at bedtime for correction alone, as this markedly raises nocturnal hypoglycemia risk 1, 2.