What is the best approach to switch a patient with impaired glucose control from daily Lantus (insulin glargine) and sliding scale insulin to a basal-bolus insulin regimen, given the patient cannot take metformin?

Switching from Lantus + Sliding Scale to Basal-Bolus Insulin

For a patient on daily Lantus and sliding scale insulin who cannot take metformin, immediately discontinue the sliding scale as monotherapy and transition to a structured basal-bolus regimen by calculating total daily insulin needs and splitting 50% as basal (Lantus) and 50% as rapid-acting prandial insulin divided among three meals. 1, 2, 3

Why Sliding Scale Must Be Discontinued Immediately

• Sliding scale insulin as sole therapy is explicitly condemned by all major diabetes guidelines and shown to be ineffective, treating hyperglycemia reactively after it occurs rather than preventing it 1, 3
• Scheduled basal-bolus regimens are superior to sliding scale monotherapy, providing better glycemic control with reduced hospital complications 1, 3
• In comparative trials, only 38% of patients on sliding scale alone achieved mean blood glucose <140 mg/dL versus 68% with proper basal-bolus therapy 1

Step 1: Calculate Total Daily Insulin Dose

Determine the patient's current total daily insulin requirement:

• Add up all Lantus doses plus any sliding scale insulin used over the past 24-48 hours 1, 2
• For patients with severe hyperglycemia (A1C ≥9% or blood glucose ≥300 mg/dL), start with weight-based dosing of 0.3-0.5 units/kg/day as total daily dose 1, 2, 4
• For patients with moderate hyperglycemia, use 0.1-0.2 units/kg/day as the starting point 1, 4

Step 2: Split the Total Daily Dose (50/50 Rule)

Divide the calculated total daily dose:

• 50% as basal insulin (Lantus) given once daily at the same time each day 1, 2, 4
• 50% as rapid-acting prandial insulin (lispro, aspart, or glulisine) divided equally among three meals 1, 2, 4

Example calculation: For a 70 kg patient with A1C of 11%:

• Total daily dose = 0.4 units/kg × 70 kg = 28 units
• Basal (Lantus) = 14 units once daily
• Prandial = 14 units total, split as approximately 5 units before breakfast, 5 units before lunch, 4 units before dinner 1, 2

Step 3: Add Correction Insulin Protocol

Implement a correction insulin protocol separate from scheduled doses:

• Use the same rapid-acting insulin as prandial doses 1
• Apply a simplified correction scale: add 2 units for pre-meal glucose >250 mg/dL, add 4 units for pre-meal glucose >350 mg/dL 1
• Never give rapid-acting insulin at bedtime to avoid nocturnal hypoglycemia 1, 2

Step 4: Titration Algorithm

Adjust basal insulin based on fasting glucose patterns:

• Increase Lantus by 2 units every 3 days if fasting glucose is 140-179 mg/dL 1, 5
• Increase Lantus by 4 units every 3 days if fasting glucose is ≥180 mg/dL 1, 5
• Target fasting glucose: 80-130 mg/dL 1, 6

Adjust prandial insulin based on postprandial glucose:

• Increase the corresponding meal's prandial dose by 1-2 units (or 10-15%) every 3 days if 2-hour postprandial glucose consistently exceeds 180 mg/dL 1, 2
• Target postprandial glucose: <180 mg/dL 1

Step 5: Monitor for Critical Threshold

Watch for overbasalization when basal insulin exceeds 0.5 units/kg/day:

• Clinical signals include: basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability 1, 5
• When basal insulin approaches 0.5-1.0 units/kg/day without achieving glycemic targets, focus on intensifying prandial insulin rather than continuing to escalate basal insulin 1, 5

Dose Adjustments for High-Risk Patients

Reduce starting doses for patients at higher hypoglycemia risk:

• For elderly patients (>65 years), those with renal failure (especially CKD stage 5), or poor oral intake, use lower starting doses of 0.1-0.25 units/kg/day 1, 2
• For type 2 diabetes with CKD stage 5, reduce total daily dose by 50% 1
• If hypoglycemia occurs without clear cause, reduce the corresponding insulin dose by 10-20% immediately 1, 2

Monitoring Requirements

Daily glucose monitoring is essential during titration:

• Check fasting glucose every morning to guide basal insulin adjustments 1, 5
• Check pre-meal glucose before each meal to calculate correction doses 1
• Check 2-hour postprandial glucose to assess adequacy of prandial insulin coverage 1
• Reassess every 3 days during active titration, and every 3-6 months once stable 1

Patient Education Essentials

Provide comprehensive education on:

• Proper insulin injection technique and site rotation within the same region (abdomen, thigh, or deltoid) 1, 6
• Recognition and treatment of hypoglycemia: treat any glucose <70 mg/dL immediately with 15 grams of fast-acting carbohydrate, recheck in 15 minutes 1
• Self-monitoring of blood glucose and recording values 1
• "Sick day" management rules and when to contact healthcare provider 1
• Insulin storage, handling, and administration timing (rapid-acting insulin 0-15 minutes before meals) 1, 2

Critical Pitfalls to Avoid

• Never continue sliding scale as monotherapy, even temporarily, as scheduled basal-bolus insulin is superior 1, 3
• Never delay insulin intensification in patients not achieving glycemic goals, as this prolongs hyperglycemia exposure and increases complication risk 1
• Never give rapid-acting insulin at bedtime for correction, as this significantly increases nocturnal hypoglycemia risk 1, 2
• Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia, as this leads to overbasalization with increased hypoglycemia risk 1, 5
• Do not dilute or mix Lantus with any other insulin or solution, as this alters the pharmacokinetic profile unpredictably 6
• Do not administer Lantus intravenously or via insulin pump, as the intended duration of activity depends on subcutaneous injection 6

Alternative Considerations Without Metformin

Since the patient cannot take metformin:

• Consider adding a GLP-1 receptor agonist to basal insulin to improve glycemic control while minimizing weight gain and hypoglycemia risk, particularly if basal insulin approaches 0.5 units/kg/day without achieving targets 1, 7
• GLP-1 receptor agonists are the preferred injectable medication before advancing to full basal-bolus insulin, providing comparable or better HbA1c reduction with lower hypoglycemia risk and weight loss rather than weight gain 1
• Evaluate for other oral agents (SGLT2 inhibitors, DPP-4 inhibitors) if not contraindicated, though these should not delay appropriate insulin intensification 1, 7