Immediate Insulin Dosing for Blood Glucose of 420 mg/dL
For a blood glucose of 420 mg/dL, you should immediately initiate basal-bolus insulin therapy with a total daily dose of 0.3-0.5 units/kg/day, split 50% as basal insulin and 50% as prandial insulin divided among meals, rather than starting with basal insulin alone. 1, 2
Why Basal-Bolus Therapy is Required
This level of severe hyperglycemia (≥300-350 mg/dL) warrants immediate basal-bolus coverage, not just basal insulin alone. 2, 1 The American Diabetes Association explicitly recommends starting basal-bolus insulin immediately for patients with blood glucose ≥300-350 mg/dL and/or HbA1c 10-12% with symptomatic or catabolic features. 1
A blood glucose of 420 mg/dL indicates both inadequate basal coverage AND significant postprandial excursions requiring mealtime insulin from the outset. 1
Specific Dosing Algorithm
Calculate Total Daily Dose
- Start with 0.3-0.5 units/kg/day as your total daily insulin dose for severe hyperglycemia. 1, 2
- For a 70 kg patient, this equals 21-35 units total daily dose (typically start at 0.4 units/kg = 28 units). 1
Split the Dose
- Give 50% as basal insulin (long-acting insulin glargine or detemir) once daily. 1, 2
- Give 50% as prandial insulin (rapid-acting insulin) divided among three meals. 1, 2
- For the 70 kg example: 14 units basal insulin once daily + approximately 5 units rapid-acting insulin before each meal. 1
Titration Protocol
Basal Insulin Adjustment
- Increase basal insulin by 4 units every 3 days if fasting glucose ≥180 mg/dL. 1, 2
- Increase by 2 units every 3 days if fasting glucose is 140-179 mg/dL. 1, 2
- Target fasting glucose: 80-130 mg/dL. 1, 2
Prandial Insulin Adjustment
- Increase prandial insulin by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings. 1
- Target postprandial glucose: <180 mg/dL. 2
Foundation Therapy
Continue metformin unless contraindicated, even when initiating insulin therapy, as it reduces total insulin requirements and provides complementary glucose-lowering effects. 1, 2, 3 The dose should be at least 1000 mg twice daily (2000 mg total) unless contraindicated. 1
Critical Monitoring Requirements
- Daily fasting blood glucose monitoring is essential during titration. 1, 2
- Check 2-hour postprandial glucose after each meal where prandial insulin is given. 1
- Reassess every 3-6 months once stable, but adjust doses every 3 days during active titration. 1
Common Pitfalls to Avoid
- Do not start with basal insulin alone when blood glucose is this elevated—you will miss the postprandial component and delay achieving control. 1, 2
- Do not delay insulin initiation by trying additional oral medications first at this glucose level. 1, 4
- Do not abruptly discontinue oral medications when starting insulin—continue metformin and discontinue sulfonylureas only if hypoglycemia occurs. 1, 3
- Do not rely on sliding scale insulin alone without scheduled basal and prandial insulin. 1
Patient Education Essentials
- Teach proper insulin injection technique and site rotation to prevent lipohypertrophy. 1, 3
- Educate on recognition and treatment of hypoglycemia (treat at ≤70 mg/dL with 15 grams of fast-acting carbohydrate). 1
- Provide written instructions for insulin dose adjustments based on self-monitoring. 1
- Emphasize timing: rapid-acting insulin should be given 0-15 minutes before meals. 1, 3
When to Reassess
If hypoglycemia occurs, determine the cause and reduce the dose by 10-20% immediately. 1, 2 Reassess adequacy of insulin dose at every clinical visit, looking for signs of overbasalization (basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia, high glucose variability). 1