What is the recommended weight‑based initial insulin dosing and titration strategy for an adult with type 1 diabetes and for an insulin‑naïve adult with type 2 diabetes?

Weight-Based Initial Insulin Dosing and Titration for Adults with Type 1 and Type 2 Diabetes

Type 1 Diabetes: Initial Dosing

Start with 0.5 units/kg/day as the total daily insulin dose (TDD) for metabolically stable adults with type 1 diabetes. This represents the standard starting point, with an acceptable range of 0.4–1.0 units/kg/day 1, 2, 3. For patients presenting with diabetic ketoacidosis or severe hyperglycemia, use higher weight-based dosing immediately 3.

Basal-Bolus Distribution

• Allocate 40–50% of TDD to basal insulin (long-acting analog such as glargine, detemir, or degludec) administered once daily 1, 2, 3, 4.
• Allocate 50–60% of TDD to prandial insulin (rapid-acting analog such as lispro, aspart, or glulisine) divided among three meals 1, 2, 3.
• Administer rapid-acting insulin 0–15 minutes before meals for optimal postprandial glucose control 1, 2, 5.

Practical Example

For a 70 kg adult with type 1 diabetes:

• TDD = 0.5 × 70 = 35 units/day
• Basal insulin = 40–50% of 35 = 14–18 units once daily
• Prandial insulin = 50–60% of 35 = 18–21 units total, divided as ≈6–7 units per meal 2, 3

Type 2 Diabetes: Initial Dosing

For insulin-naïve adults with type 2 diabetes, start basal insulin at 10 units once daily OR 0.1–0.2 units/kg/day, administered at the same time each day. Continue metformin (unless contraindicated) and possibly one additional non-insulin agent 1, 2, 6.

When to Use Higher Starting Doses

• For severe hyperglycemia (HbA1c ≥9%, blood glucose ≥300–350 mg/dL, or symptomatic/catabolic features), start with 0.3–0.5 units/kg/day as total daily dose, split 50% basal and 50% prandial insulin from the outset 1, 2.
• This basal-bolus approach is required immediately in severe cases rather than basal-only therapy 1, 2.

Basal Insulin Titration Algorithm

Increase basal insulin systematically based on fasting glucose:

Fasting Glucose	Dose Adjustment	Frequency
140–179 mg/dL	Increase by 2 units	Every 3 days
≥180 mg/dL	Increase by 4 units	Every 3 days
Target: 80–130 mg/dL

1, 2, 6

• If unexplained hypoglycemia occurs (glucose <70 mg/dL), reduce the implicated dose by 10–20% immediately before waiting for the next scheduled adjustment 1, 2.
• Daily fasting glucose monitoring is essential during titration to guide adjustments 1, 2.

Critical Threshold: When to Stop Basal Escalation

When basal insulin approaches 0.5–1.0 units/kg/day without achieving glycemic targets, STOP further basal increases and add prandial insulin instead. Continuing to escalate basal insulin beyond this threshold leads to "over-basalization" with increased hypoglycemia risk and suboptimal control 1, 2.

Clinical Signals of Over-Basalization

• Basal dose >0.5 units/kg/day
• Bedtime-to-morning glucose differential ≥50 mg/dL
• Episodes of hypoglycemia despite overall hyperglycemia
• High glucose variability throughout the day 1, 2

Adding Prandial Insulin in Type 2 Diabetes

Initiate prandial insulin when:

• Basal insulin has been optimized (fasting glucose 80–130 mg/dL) but HbA1c remains above target after 3–6 months 1, 2
• Basal insulin dose approaches 0.5–1.0 units/kg/day without achieving HbA1c goals 1, 2

Prandial Insulin Starting Dose

• Begin with 4 units of rapid-acting insulin before the largest meal 1, 2
• Alternative: Use 10% of the current basal dose (e.g., 40 units basal → 4 units prandial) 1, 2

Prandial Insulin Titration

• Adjust each meal dose by 1–2 units (≈10–15%) every 3 days based on 2-hour postprandial glucose readings 1, 2
• Target postprandial glucose <180 mg/dL 1, 2
• If hypoglycemia occurs, reduce the corresponding dose by 10–20% immediately 1, 2

Special Populations Requiring Dose Adjustments

High-Risk Patients (Elderly, Renal Impairment, Poor Oral Intake)

• Start with 0.1–0.25 units/kg/day to minimize hypoglycemia risk 1, 2
• For hospitalized patients on high-dose home insulin (≥0.6 units/kg/day), reduce total daily dose by 20% upon admission 1, 2

Chronic Kidney Disease

• CKD Stage 5 with type 2 diabetes: Reduce total daily insulin by 50% 2
• CKD Stage 5 with type 1 diabetes: Reduce total daily insulin by 35–40% 2

Foundation Therapy: Continue Metformin

Metformin should be continued at maximum tolerated dose (up to 2,000–2,550 mg/day) when adding or intensifying insulin therapy in type 2 diabetes. This combination reduces total insulin requirements by 20–30% and provides superior glycemic control compared with insulin alone 1, 2.

Common Pitfalls to Avoid

• Never delay insulin initiation in patients not achieving glycemic goals with oral medications; prolonged hyperglycemia increases complication risk 1, 2.
• Never discontinue metformin when starting insulin unless contraindicated; this leads to higher insulin requirements and greater weight gain 1, 2.
• Never continue escalating basal insulin beyond 0.5–1.0 units/kg/day without addressing postprandial hyperglycemia; this causes over-basalization with increased hypoglycemia and suboptimal control 1, 2.
• Never use sliding-scale insulin as monotherapy; major diabetes guidelines condemn this reactive approach as ineffective and unsafe 1, 2.

Expected Clinical Outcomes

• With properly implemented basal-bolus therapy, ≈68% of patients achieve mean glucose <140 mg/dL, versus ≈38% with sliding-scale insulin alone 1, 2.
• HbA1c reductions of 2–3% (or 3–4% in severe hyperglycemia) are achievable over 3–6 months with intensive titration 1, 2.
• Correctly executed basal-bolus regimens do not increase overall hypoglycemia incidence compared with inadequate sliding-scale approaches 1, 2.