In a 60‑kg adult with type 2 diabetes on metformin, should I start only basal insulin or also add a pre‑meal (bolus) insulin?

Start with Basal Insulin Only

In a 60-kg adult with type 2 diabetes on metformin, you should start with basal insulin alone and only add prandial (bolus) insulin later if A1C remains above goal despite optimized basal insulin. 1

Initial Approach: Basal Insulin Monotherapy

The 2025 ADA Standards of Care provide a clear algorithmic approach 1:

• Start basal insulin (e.g., NPH or long-acting analog) at 10 units/day OR 0.1-0.2 units/kg/day (6-12 units for this 60-kg patient)
• Continue metformin 1
• Titrate basal insulin every 3 days by 2 units to reach fasting plasma glucose goal (90-130 mg/dL) without hypoglycemia
• Assess adequacy at every visit by monitoring for signs of "overbasalization"

When to Add Prandial Insulin

Only add prandial insulin if A1C remains above goal despite optimized basal insulin. 1 Look for these clinical signals indicating need for intensification:

• Elevated bedtime-to-morning glucose differential
• Elevated postprandial-to-preprandial glucose differential
• Hypoglycemia (aware or unaware)
• High glucose variability
• A1C persistently above individualized goal

Stepwise Prandial Insulin Addition

If intensification is needed 1:

1. Start with ONE prandial injection before the largest meal or meal causing greatest postprandial glucose excursion

   • Begin with 4 units or 10% of basal dose
   • This "basal-plus" approach is simpler, causes less weight gain, and has lower hypoglycemia risk than full basal-bolus 2, 3

2. Add second and third prandial doses only if A1C remains elevated

   • Progress stepwise based on individual postprandial glucose patterns
   • Eventually may require full basal-bolus regimen (basal + 3 prandial injections)

Important Caveats

Consider GLP-1 receptor agonists before adding prandial insulin if the patient is not already on one 1. These agents:

• Improve postprandial glucose control
• Provide comparable A1C reduction to prandial insulin 4
• Cause no weight gain (often weight loss)
• Have minimal hypoglycemia risk
• May offer cardiovascular benefits

Common pitfall: Starting full basal-bolus therapy immediately. This increases injection burden, hypoglycemia risk, and weight gain unnecessarily. Most patients achieve adequate control with basal insulin alone or basal-plus-one strategy for extended periods 2, 5.

The evidence strongly supports a conservative, stepwise approach—start simple with basal insulin, then intensify only as metabolic needs dictate.