What is the recommended initial dose of Humalog (insulin lispro) when adding it to a sliding scale regimen for a patient with diabetes, considering their current medication regimen and insulin sensitivity?

Adding Humalog for Sliding Scale Coverage

Start with 4 units of Humalog (insulin lispro) before the largest meal or use 10% of the current basal insulin dose, and implement a simplified correction scale: 2 units for premeal glucose >250 mg/dL and 4 units for premeal glucose >350 mg/dL. 1, 2

Initial Prandial Insulin Dosing

When adding Humalog to an existing regimen, the American Diabetes Association provides three evidence-based starting approaches 1:

• 4 units per dose (standard starting dose)
• 0.1 units/kg body weight (weight-based approach)
• 10% of current basal insulin dose (proportional method)

Begin with a single injection before the meal causing the greatest postprandial glucose excursion, typically the largest meal of the day 1, 2. This stepwise approach allows for safer titration and reduces hypoglycemia risk compared to starting multiple prandial doses simultaneously 1.

Simplified Sliding Scale Protocol

For correction insulin alongside scheduled prandial doses, implement this standardized approach 3, 2:

• Premeal glucose >250 mg/dL (13.9 mmol/L): Add 2 units of Humalog
• Premeal glucose >350 mg/dL (19.4 mmol/L): Add 4 units of Humalog

This sliding scale should serve as an adjunct to scheduled basal-bolus therapy, never as monotherapy 3, 1. Sliding scale insulin alone is explicitly condemned by all major diabetes guidelines, as it treats hyperglycemia reactively rather than preventing it, leading to dangerous glucose fluctuations 1, 4.

Timing of Administration

Administer Humalog 0-15 minutes before meals for optimal postprandial glucose control 1. The rapid-acting analog has a duration of action of only 3-5 hours and is specifically designed to blunt post-meal glucose excursions 1.

Critical pitfall: Never give rapid-acting insulin at bedtime, as this significantly increases nocturnal hypoglycemia risk 3, 1, 2.

Titration Algorithm

Adjust Humalog doses systematically based on glucose response 1, 2:

• Increase by 1-2 units or 10-15% every 3 days if 2-hour postprandial glucose consistently exceeds 180 mg/dL
• Decrease by 10-20% if hypoglycemia occurs without clear cause
• Target postprandial glucose: <180 mg/dL for most adults

Monitor premeal and 2-hour postprandial glucose values to guide adjustments 1. If 50% of premeal values over 2 weeks remain above target, intensify the regimen 3.

Basal Insulin Adjustment Considerations

If adding prandial insulin when A1C is <8%, consider reducing basal insulin by 4 units or 10% to prevent hypoglycemia 2. This prevents "insulin stacking" when transitioning from basal-only to basal-bolus therapy 1.

Critical threshold: When basal insulin exceeds 0.5 units/kg/day without achieving glycemic targets, adding prandial coverage becomes more appropriate than continuing to escalate basal insulin alone 1. Signs of "overbasalization" include bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability 1.

Intensification Strategy

If single-meal prandial dosing proves insufficient after 2-4 weeks 1, 2:

1. Add Humalog to a second meal (typically the next largest meal)
2. Progress to three-meal coverage if needed for optimal control
3. Maintain metformin throughout intensification unless contraindicated 1
4. Consider discontinuing sulfonylureas when advancing beyond basal-only insulin to prevent hypoglycemia 1

Special Population Considerations

For older adults or frail patients, use a simplified approach with more conservative targets 3, 2:

• Target premeal glucose: 90-150 mg/dL (5.0-8.3 mmol/L) rather than 80-130 mg/dL
• Consider discontinuing sliding scale when not needed daily to reduce medication burden
• Use lower correction thresholds to minimize hypoglycemia risk

For hospitalized patients, the basal-bolus approach with 50:50 split between basal and bolus insulin provides superior glycemic control compared to sliding scale monotherapy, with reduced hospital complications 1, 4.

Monitoring Requirements

• Check premeal glucose immediately before each meal to calculate correction doses 1
• Check 2-hour postprandial glucose to assess adequacy of carbohydrate coverage 1
• Reassess every 2 weeks during active titration 3, 2
• Stop sliding scale when not needed daily 3

Common Pitfalls to Avoid

Never rely on sliding scale insulin as monotherapy 1, 4. Randomized trials demonstrate that scheduled basal-bolus regimens provide better glycemic control with reduced hospital complications compared to sliding scale alone 1, 4.

Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia 1. This leads to overbasalization with increased hypoglycemia risk and suboptimal control 1.

Never give Humalog at bedtime unless closely monitoring, as this significantly increases nocturnal hypoglycemia risk 3, 1.