What is the difference between using sliding scale insulin and basal insulin, such as glargine (insulin glargine) or detemir (insulin detemir), in a patient with diabetes?

Sliding Scale Insulin vs Basal Insulin: A Critical Comparison

Sliding Scale Insulin Should Be Abandoned as Monotherapy

Sliding scale insulin as the sole treatment is explicitly condemned by all major diabetes guidelines and should be immediately discontinued in favor of scheduled basal insulin therapy. 1, 2

Sliding scale insulin (SSI) treats hyperglycemia reactively after it occurs rather than preventing it, leading to dangerous glucose fluctuations and suboptimal glycemic control. 1 In contrast, basal insulin analogs like glargine (Lantus) or detemir (Levemir) provide consistent, predictable 24-hour coverage that addresses the underlying pathophysiology of diabetes. 1, 3

Why Basal Insulin is Superior

Efficacy and Glycemic Control

• Basal-bolus insulin regimens provide better glycemic control than sliding scale alone, with 68% of patients achieving mean blood glucose <140 mg/dL versus only 38% with sliding scale monotherapy. 1
• Scheduled basal insulin with correction doses as adjunct is superior to SSI monotherapy, reducing hospital complications in general surgery patients with type 2 diabetes. 1, 2
• Basal insulin addresses fasting and between-meal glucose levels by restraining hepatic glucose production, providing the foundation for diabetes management. 1, 3

Safety Profile

• Both glargine and detemir demonstrate lower within-subject variability compared to NPH insulin, resulting in more predictable glucose control. 4
• Insulin detemir shows lower risk of hypoglycemia and a weight-sparing effect compared to NPH insulin and even glargine in some studies. 4
• No significant difference in hypoglycemia rates exists between detemir and glargine in hospitalized patients. 5

Initiating Basal Insulin: Practical Algorithm

Starting Doses

For insulin-naive patients with type 2 diabetes:

• Start with 10 units once daily OR 0.1-0.2 units/kg body weight. 1, 3, 2
• For severe hyperglycemia (HbA1c ≥10-12% with symptoms), consider 0.3-0.5 units/kg/day as total daily dose, split between basal and prandial insulin. 1, 2

For type 1 diabetes:

• Total daily insulin requirement: 0.4-1.0 units/kg/day, with approximately 50% as basal insulin. 1, 3
• Typical starting dose for metabolically stable patients: 0.5 units/kg/day. 1, 3

Titration Protocol

• If fasting glucose 140-179 mg/dL: Increase basal insulin by 2 units every 3 days. 1, 3
• If fasting glucose ≥180 mg/dL: Increase basal insulin by 4 units every 3 days. 1, 3
• Target fasting glucose: 80-130 mg/dL. 1, 3
• If hypoglycemia occurs: Reduce dose by 10-20% immediately. 1, 3

Critical Threshold: When to Stop Escalating Basal Insulin

When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, add prandial insulin rather than continuing to escalate basal insulin alone. 1, 3

Clinical signals of "overbasalization" include:

• Basal dose >0.5 units/kg/day 1, 3
• Bedtime-to-morning glucose differential ≥50 mg/dL 1, 3
• Episodes of hypoglycemia 1, 3
• High glucose variability throughout the day 1, 3

Pharmacokinetic Differences: Glargine vs Detemir

Insulin Glargine

• Provides relatively flat 24-hour coverage with once-daily dosing in most patients. 3
• May require twice-daily dosing in type 1 diabetes with high glycemic variability. 3

Insulin Detemir

• Duration of action ranges from 5.7 to 23.2 hours depending on dose. 6
• Terminal half-life of 5-7 hours. 6
• More than 98% bound to albumin in bloodstream, resulting in slower distribution to peripheral tissues. 6
• May require twice-daily dosing more frequently than glargine, with only 45% of patients remaining on once-daily dosing in some studies. 7
• When converting from glargine to detemir, the total daily dose of detemir should be approximately 38% higher to achieve equivalent glycemic control. 3

Foundation Therapy: Continue Metformin

Metformin must be continued at maximum tolerated dose (up to 2000-2500 mg daily) when adding insulin therapy unless contraindicated. 1, 3, 2

This combination provides superior glycemic control with reduced insulin requirements and less weight gain compared to insulin alone. 1, 3

Common Pitfalls to Avoid

• Never delay insulin initiation in patients not achieving glycemic goals with oral medications, as this prolongs hyperglycemia exposure and increases complication risk. 1, 3, 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, 3
• Never use sliding scale insulin as monotherapy even temporarily, as scheduled basal insulin with correction doses as adjunct is superior. 1, 2
• Never discontinue metformin when starting insulin unless contraindicated, as this leads to higher insulin requirements and more weight gain. 1, 3

Special Populations

Hospitalized Patients

• For insulin-naive or low-dose insulin patients: Start 0.3-0.5 units/kg/day total daily dose, with half as basal insulin. 3
• For patients on high-dose home insulin (≥0.6 units/kg/day): Reduce total daily dose by 20% to prevent hypoglycemia. 3
• For high-risk patients (elderly >65 years, renal failure, poor oral intake): Use lower doses of 0.1-0.25 units/kg/day. 3

Chronic Kidney Disease

• For type 2 diabetes with CKD stage 5: Reduce total daily insulin dose by 50%. 3
• For type 1 diabetes with CKD stage 5: Reduce total daily insulin dose by 35-40%. 3