Insulin 70/30 Dosing for a 73‑kg Woman with HbA1c 8.7%
Do Not Use Premixed 70/30 Insulin—Start Basal Insulin Glargine Instead
Premixed 70/30 insulin is contraindicated as initial therapy for this patient. Randomized trials demonstrate a 64% hypoglycemia rate with premixed formulations versus 24% with basal‑bolus regimens in hospitalized patients, leading to early trial termination 1. The fixed 70:30 basal‑to‑prandial ratio cannot be adjusted independently, increasing hypoglycemia risk when meal intake varies 1. Major diabetes guidelines do not recommend premixed 70/30 insulin for initial insulin therapy 1.
Initial Insulin Regimen: Basal Insulin Glargine (Lantus)
Starting Dose
- Begin with 10 units of insulin glargine once daily (or 0.1–0.2 units/kg/day = 7–15 units for a 73‑kg patient), administered at the same time each day, preferably at bedtime 1.
- For an HbA1c of 8.7%, the standard starting dose of 10 units once daily is appropriate 1.
- Continue metformin at maximum tolerated dose (up to 2000 mg daily) unless contraindicated, as this combination reduces total insulin requirements by 20–30% 1.
Titration Protocol
- Increase basal insulin by 2 units every 3 days if fasting glucose is 140–179 mg/dL 1.
- Increase basal insulin by 4 units every 3 days if fasting glucose is ≥180 mg/dL 1.
- Target fasting glucose: 80–130 mg/dL 1.
- If unexplained hypoglycemia (<70 mg/dL) occurs, reduce the dose by 10–20% immediately 1.
When to Add Prandial Insulin
Critical Threshold for Basal Escalation
- When basal insulin approaches 0.5–1.0 units/kg/day (36–73 units for this patient) without achieving HbA1c goals, add prandial insulin rather than continuing to escalate basal insulin alone 1.
- Clinical signals of "over‑basalization" include:
Initiating Prandial Insulin
- Start with 4 units of rapid‑acting insulin (lispro, aspart, or glulisine) before the largest meal, or use 10% of the current basal dose 1.
- Administer rapid‑acting insulin 0–15 minutes before meals 1.
- Titrate each meal dose by 1–2 units (10–15%) every 3 days based on 2‑hour post‑prandial glucose, targeting <180 mg/dL 1.
Monitoring Requirements
- Check fasting glucose daily during the titration phase to guide basal insulin adjustments 1.
- Once prandial insulin is added, measure glucose before each meal and at bedtime 1.
- Reassess HbA1c every 3 months until stable, then every 3–6 months 1.
Expected Clinical Outcomes
- With properly implemented basal insulin therapy, ≈68% of patients achieve mean glucose <140 mg/dL, compared with ≈38% on sliding‑scale insulin alone 1.
- For an HbA1c of 8.7%, expect an HbA1c reduction of 1.5–2% over 3–6 months with basal insulin plus metformin 1.
- If basal insulin alone is insufficient after 3–6 months, adding prandial insulin typically yields an additional 1–1.5% HbA1c reduction 1.
Common Pitfalls to Avoid
- Do not use premixed 70/30 insulin as initial therapy—it carries excessive hypoglycemia risk and lacks dosing flexibility 1.
- Do not delay insulin initiation in patients not achieving glycemic goals with oral medications, as this prolongs hyperglycemia exposure and increases complication risk 1.
- Do not discontinue metformin when starting insulin unless contraindicated, as this leads to higher insulin requirements and more weight gain 1.
- Do not continue escalating basal insulin beyond 0.5–1.0 units/kg/day without addressing post‑prandial hyperglycemia, as this leads to over‑basalization with increased hypoglycemia risk 1.
- Never use sliding‑scale insulin as monotherapy—it is condemned by major diabetes guidelines as ineffective and unsafe 1.
Patient Education Essentials
- Insulin injection technique and site rotation to prevent lipohypertrophy 1.
- Hypoglycemia recognition and treatment: symptoms, <70 mg/dL threshold, 15‑g carbohydrate rule 1.
- Sick‑day management: continue insulin even if not eating, check glucose every 4 hours, maintain hydration 1.
- Glucose monitoring: at least daily fasting measurements during titration 1.