How should I initiate and titrate basal insulin therapy in an adult with type 2 diabetes mellitus, including initial weight‑based dosing, titration schedule, and indications for adding rapid‑acting prandial insulin?

How to Start and Titrate Insulin in Type 2 Diabetes

Initial Basal Insulin Dosing

Start with 10 units of basal insulin (glargine, detemir, or degludec) once daily OR 0.1–0.2 units/kg body weight, administered at the same time each day. 1

• For patients with severe hyperglycemia (A1C ≥9%, blood glucose ≥300 mg/dL, or symptomatic/catabolic features), consider higher starting doses of 0.3–0.5 units/kg/day using a basal-bolus regimen from the outset 1
• Continue metformin (unless contraindicated) and possibly one additional non-insulin agent when starting basal insulin 1
• Prescribe glucagon for emergent hypoglycemia 1

Basal Insulin Titration Protocol

Set a fasting plasma glucose (FPG) target of 80–130 mg/dL and increase the dose by 2–4 units every 3 days until this target is reached without hypoglycemia. 1

Specific titration algorithm:

• If FPG is 140–179 mg/dL: increase by 2 units every 3 days 1
• If FPG is ≥180 mg/dL: increase by 4 units every 3 days 1
• If hypoglycemia occurs without clear cause: reduce dose by 10–20% immediately 1
• If >2 fasting values per week are <80 mg/dL: decrease by 2 units 1

Daily fasting blood glucose monitoring is essential during titration. 1

Critical Threshold: Recognizing Overbasalization

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, stop escalating basal insulin and add prandial insulin or a GLP-1 receptor agonist instead. 1

Clinical signals of overbasalization include:

• Basal insulin dose >0.5 units/kg/day 1
• Bedtime-to-morning glucose differential ≥50 mg/dL 1
• Hypoglycemia (aware or unaware) 1
• High glucose variability 1

Continuing to escalate basal insulin beyond this threshold leads to suboptimal control and increased hypoglycemia risk without improved glycemic outcomes. 1

When to Add Prandial Insulin

Add prandial insulin when basal insulin has been optimized (FPG 80–130 mg/dL) but A1C remains above target after 3–6 months, OR when basal insulin dose approaches 0.5–1.0 units/kg/day without achieving A1C goal. 1

Prandial insulin initiation:

• Start with 4 units of rapid-acting insulin (lispro, aspart, or glulisine) before the largest meal OR the meal with greatest postprandial glucose excursion 1
• Alternatively, use 10% of the current basal dose 1
• If A1C <8% (<64 mmol/mol), consider lowering the basal dose by 4 units or 10% when adding prandial insulin 1

Prandial insulin titration:

• Increase dose by 1–2 units OR 10–15% twice weekly based on 2-hour postprandial glucose readings 1
• Target postprandial glucose <180 mg/dL 1
• For hypoglycemia without clear cause: reduce corresponding dose by 10–20% 1

Administer rapid-acting insulin 0–15 minutes before meals for optimal postprandial control. 1

Stepwise Intensification Beyond Single Prandial Dose

If A1C remains above target after adding one prandial injection, add additional prandial insulin injections stepwise (two, then three injections) before other meals based on postprandial glucose patterns. 1

This eventually leads to a full basal-bolus regimen with basal insulin once daily and rapid-acting insulin before each of three meals. 1

Alternative: GLP-1 Receptor Agonist Combination

If not already on a GLP-1 RA or dual GIP/GLP-1 RA, strongly consider adding these agents (either as free combination or fixed-ratio combination) before advancing to prandial insulin. 1

• GLP-1 RAs combined with basal insulin provide potent glucose-lowering with less weight gain and hypoglycemia than intensified insulin regimens 1
• Fixed-ratio combinations (IDegLira or iGlarLixi) are available for patients on both therapies 1

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
• Never discontinue metformin when starting insulin unless contraindicated—this leads to higher insulin requirements and more weight gain 1
• Never continue escalating basal insulin beyond 0.5–1.0 units/kg/day without addressing postprandial hyperglycemia—this causes overbasalization with increased hypoglycemia and suboptimal control 1
• Never use sliding-scale insulin as monotherapy—it treats hyperglycemia reactively rather than preventing it, leading to dangerous glucose fluctuations 1
• Never give rapid-acting insulin at bedtime as a sole correction dose—this markedly raises nocturnal hypoglycemia risk 1

Reassessment Schedule

Reassess and modify therapy every 3–6 months to avoid therapeutic inertia. 1 Assess adequacy of insulin dose at every clinical visit, looking specifically for signs of overbasalization. 1