What is the recommended insulin dosage for a patient with diabetes, considering factors such as type and severity of diabetes, body weight, and renal function?

Insulin Dosing in Diabetes

For Type 2 diabetes, start with 10 units once daily or 0.1-0.2 units/kg body weight of basal insulin (such as insulin glargine), administered at the same time each day, and titrate by 2-4 units every 3 days until fasting glucose reaches 80-130 mg/dL. 1, 2, 3

Type 2 Diabetes: Initial Dosing Algorithm

Standard Initiation (HbA1c <9%)

• Begin with 10 units once daily or 0.1-0.2 units/kg/day of basal insulin (glargine, detemir, or degludec) 1, 2, 3
• Continue metformin unless contraindicated, and possibly one additional non-insulin agent 1, 2
• Administer at the same time each day (any time, but consistent) 2, 3

Severe Hyperglycemia (HbA1c ≥9% or glucose ≥300-350 mg/dL)

• Start with basal-bolus insulin immediately when HbA1c is 10-12% with symptomatic or catabolic features (weight loss, ketosis) 1, 2
• Use higher starting doses of 0.3-0.5 units/kg/day as total daily dose, split 50% basal and 50% prandial 2, 4
• This aggressive approach is warranted when blood glucose exceeds 300 mg/dL or HbA1c exceeds 10% 1, 2

Titration Protocol

• Increase by 2 units every 3 days if fasting glucose is 140-179 mg/dL 2, 4
• Increase by 4 units every 3 days if fasting glucose is ≥180 mg/dL 2, 4
• Target fasting plasma glucose: 80-130 mg/dL 1, 2, 4
• If hypoglycemia occurs, reduce dose by 10-20% immediately 2, 4

Critical Threshold: When to Add Prandial Insulin

• Stop escalating basal insulin when dose exceeds 0.5 units/kg/day and add prandial insulin instead 1, 2
• Signs of "overbasalization" include: basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia, and high glucose variability 2
• Start prandial insulin with 4 units before the largest meal or 10% of current basal dose 2

Type 1 Diabetes: Initial Dosing Algorithm

Standard Starting Dose

• Begin with 0.5 units/kg/day as total daily dose for metabolically stable patients 2, 5, 3
• Acceptable range: 0.4-1.0 units/kg/day 2, 5
• Split approximately 50% as basal insulin and 50% as prandial insulin divided among three meals 2, 5

Special Populations

• Honeymoon phase: Lower doses of 0.2-0.6 units/kg/day may be sufficient 2, 5
• Puberty, pregnancy, or acute illness: Higher doses approaching or exceeding 1.0 units/kg/day are required 2, 5
• Diabetic ketoacidosis: Higher weight-based dosing than standard 0.5 units/kg/day is needed 5

Distribution Example

For a 70 kg patient with Type 1 diabetes:

• Total daily dose: 0.5 × 70 = 35 units/day 5
• Basal insulin (glargine): 17-18 units once daily 5
• Prandial insulin (lispro/aspart): 17-18 units total, divided as approximately 6 units before each meal 5

Hospitalized Patients: Special Considerations

Non-Critically Ill Patients

• Insulin-naive or low-dose: Start with 0.3-0.5 units/kg/day total daily dose, giving half as basal insulin 2
• High-dose home insulin (≥0.6 units/kg/day): Reduce total daily dose by 20% upon admission to prevent hypoglycemia 2
• High-risk patients (elderly >65 years, renal failure, poor oral intake): Use lower doses of 0.1-0.25 units/kg/day 2

Perioperative Management

• Reduce basal insulin by 25% the evening before surgery to achieve target glucose with lower hypoglycemia risk 1
• Monitor blood glucose every 2-4 hours while NPO 1
• Target perioperative glucose: 80-180 mg/dL 1

Renal Function Considerations

• Patients with renal impairment require dose reduction and should start at the lower end of dosing ranges (0.1 units/kg/day for Type 2) 2, 4
• Insulin requirements decrease as renal function declines due to reduced insulin clearance 2
• Monitor more frequently for hypoglycemia in patients with chronic kidney disease 2

Body Weight Adjustments

Calculating Weight-Based Doses

• For a 50 kg patient with Type 2 diabetes: 0.1-0.2 units/kg = 5-10 units once daily (typically start with 10 units) 2
• For a 100 kg patient with Type 2 diabetes: 0.1-0.2 units/kg = 10-20 units once daily 2
• For a 70 kg patient with Type 1 diabetes: 0.5 units/kg = 35 units total daily (17-18 units basal, 17-18 units prandial) 5

Obesity Considerations

• Obese patients with Type 2 diabetes may require higher doses due to insulin resistance 2
• When basal insulin approaches 1.0 units/kg/day without achieving targets, add prandial insulin or GLP-1 receptor agonist rather than continuing to escalate 2

Common Pitfalls to Avoid

• Never delay insulin initiation in patients not achieving glycemic goals with oral medications—this prolongs hyperglycemia exposure and increases complication risk 1, 2
• Do not continue escalating basal insulin beyond 0.5-1.0 units/kg/day without adding prandial coverage—this causes overbasalization with hypoglycemia and suboptimal control 2
• Never abruptly discontinue metformin when starting insulin—continue unless contraindicated 1, 2
• Do not wait longer than 3 days between dose adjustments in stable patients—this unnecessarily prolongs time to glycemic targets 2
• Never dilute or mix insulin glargine with any other insulin or solution due to its low pH 3
• Do not use premixed insulins in hospitalized patients—they have unacceptably high rates of hypoglycemia 2

Monitoring Requirements

• Daily fasting blood glucose monitoring is essential during titration 2, 4
• Assess adequacy of insulin dose at every clinical visit 2
• Check HbA1c every 3 months during intensive titration 2
• Monitor for signs of overbasalization: hypoglycemia, high glucose variability, bedtime-to-morning differential ≥50 mg/dL 2