What is sliding‑scale insulin and how should it be used in a patient on optimized metformin 2000 mg daily and basal insulin achieving fasting glucose targets but with post‑prandial glucose >140 mg/dL, hemoglobin A1c >7 % and estimated glomerular filtration rate >30 mL/min/1.73 m²?

What is Sliding‑Scale Insulin and How Should It Be Used?

Sliding‑scale insulin (SSI) is a reactive correction‑dose strategy that treats hyperglycemia after it occurs, and it should NOT be used as monotherapy—instead, it must supplement a scheduled basal‑bolus regimen in patients requiring insulin therapy.

---

Definition and Mechanism of Sliding‑Scale Insulin

• Sliding‑scale insulin is a reactive approach that administers short‑ or rapid‑acting insulin in response to elevated blood glucose readings, typically using a predetermined dose table (e.g., 2 units for glucose >250 mg/dL, 4 units for >350 mg/dL). 1
• SSI treats hyperglycemia after it has already occurred rather than preventing it, leading to wide glucose fluctuations that exacerbate both hyper‑ and hypoglycemia. 1
• The practice has been in use for more than 80 years without robust evidence supporting its effectiveness as a standalone regimen. 2

---

Why Sliding‑Scale Insulin Alone Fails

Ineffectiveness as Monotherapy

• Only ≈38% of hospitalized patients managed with SSI alone achieve a mean glucose <140 mg/dL, compared with ≈68% using a scheduled basal‑bolus regimen. 1, 3
• SSI monotherapy is associated with clinically significant hyperglycemia, poor overall glycemic control, and increased hospital complications including postoperative wound infections and acute renal failure. 1, 3
• In one study, appropriately timed successive glucose measurements documented a decrement to target range (90–130 mg/dL) after only 12% of SSI injections, while glucose remained elevated after 84% of injections. 4

Guideline Condemnation

• The American Diabetes Association (ADA) and all major diabetes guideline societies explicitly condemn SSI as monotherapy for hospitalized patients, recommending its immediate discontinuation in favor of scheduled basal‑bolus therapy. 1, 3, 5
• SSI should never be used as the sole regimen in type 1 diabetes, as it can precipitate diabetic ketoacidosis. 1, 6

Practical Deficiencies

• SSI regimens are often left unchanged throughout hospital stays even when glucose control remains poor, with 81% of patients receiving no regimen adjustments despite persistent hyperglycemia. 4
• Uncertainties or missing information related to execution, timing, glucose levels, or insulin dose were present in ≈30% of all anticipated points of care involving SSI. 4

---

Proper Role of Correction Insulin

Correction Doses as Adjunct Only

• Correction insulin must supplement—not replace—scheduled basal and prandial insulin. 1, 6, 3
• Frequent need for correction doses signals that scheduled insulin doses are insufficient; clinicians should increase the basal or prandial components rather than rely on reactive corrections. 1, 3

Simplified Correction Protocol

• Add 2 units of rapid‑acting insulin for pre‑meal glucose >250 mg/dL. 1, 6
• Add 4 units for pre‑meal glucose >350 mg/dL. 1, 6
• These correction doses are administered in addition to scheduled prandial insulin, not as a replacement. 1, 6

Individualized Correction Dosing

• Calculate an insulin sensitivity factor (ISF) = 1500 ÷ total daily insulin dose for regular insulin or 1700 ÷ total daily insulin dose for rapid‑acting analogs. 1, 6
• Correction dose = (Current glucose – Target glucose) ÷ ISF. 1, 6

---

Recommended Basal‑Bolus Regimen Structure

For Your Patient (Metformin 2000 mg, Basal Insulin, Fasting Glucose at Target, Post‑Prandial >140 mg/dL, HbA1c >7%)

This patient requires the addition of prandial insulin, not sliding‑scale insulin alone.

Step 1: Initiate Prandial Insulin

• Start with 4 units of rapid‑acting insulin (lispro, aspart, or glulisine) before the largest meal or the meal causing the greatest post‑prandial glucose excursion. 1, 6
• Alternatively, use 10% of the current basal insulin dose as the initial prandial amount. 1, 6
• Administer prandial insulin 0–15 minutes before meals for optimal post‑prandial control. 1, 6, 3

Step 2: Titrate Prandial Insulin

• Increase each meal dose by 1–2 units (≈10–15%) every 3 days based on the 2‑hour post‑prandial glucose reading. 1, 6, 3
• Target post‑prandial glucose <180 mg/dL. 1, 6, 3
• If unexplained hypoglycemia (<70 mg/dL) occurs, reduce the implicated dose by 10–20% immediately. 1, 6, 3

Step 3: Add Correction Doses (Adjunct Only)

• Use the simplified correction protocol above (2 units for >250 mg/dL, 4 units for >350 mg/dL) in addition to scheduled prandial doses. 1, 6

Step 4: Continue Metformin

• Continue metformin at 2000 mg daily unless contraindicated; this combination reduces total insulin requirements by 20–30% and provides superior glycemic control. 1, 6

Step 5: Monitor and Adjust

• Check pre‑meal glucose before each meal to calculate correction doses. 1, 6
• Obtain 2‑hour post‑prandial glucose after each meal to assess prandial adequacy. 1, 6, 3
• Measure fasting glucose daily to guide basal insulin adjustments. 1, 6
• Reassess HbA1c every 3 months during intensive titration. 1, 6

---

When Sliding‑Scale Insulin Might Be Acceptable (Rare Exceptions)

• Mild stress hyperglycemia in patients without pre‑existing diabetes. 3, 5
• Patients with well‑controlled diabetes (HbA1c <7%) on minimal home therapy who have mild hyperglycemia during hospitalization. 3
• Patients who are NPO with no nutritional replacement and only mild hyperglycemia. 3
• Patients who are new to steroids or tapering steroids. 3

Even in these scenarios, SSI should be used cautiously and transitioned to scheduled insulin if hyperglycemia persists.

---

Critical Pitfalls to Avoid

• Never use SSI as monotherapy in patients requiring insulin therapy; this approach is condemned by all major diabetes guidelines and leads to dangerous glucose fluctuations. 1, 3, 5
• Never delay adding prandial insulin when basal insulin alone fails to achieve post‑prandial glucose targets. 1, 6
• Never give rapid‑acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk. 1, 6, 3
• Never rely solely on correction doses without adjusting scheduled basal and prandial insulin; this perpetuates inadequate control. 1, 3
• Never continue escalating basal insulin beyond 0.5–1.0 units/kg/day without addressing post‑prandial hyperglycemia, as this leads to "over‑basalization" and increased hypoglycemia risk. 1, 6

---

Expected Clinical Outcomes with Proper Basal‑Bolus Therapy

• ≈68% of patients achieve mean glucose <140 mg/dL with scheduled basal‑bolus therapy, versus ≈38% with SSI alone. 1, 3
• HbA1c reductions of 2–3% are achievable over 3–6 months with intensive insulin titration combined with metformin. 1, 6
• Properly executed basal‑bolus regimens do not increase overall hypoglycemia incidence compared with inadequate SSI approaches. 1, 3

---

Summary Algorithm for Your Patient

1. Discontinue reliance on SSI alone for post‑prandial hyperglycemia. 1, 3
2. Add prandial insulin (4 units before the largest meal or 10% of basal dose). 1, 6
3. Titrate prandial insulin by 1–2 units every 3 days based on 2‑hour post‑prandial glucose. 1, 6, 3
4. Use correction doses (2 units for >250 mg/dL, 4 units for >350 mg/dL) in addition to scheduled prandial insulin. 1, 6
5. Continue metformin at 2000 mg daily. 1, 6
6. Monitor closely: pre‑meal glucose, 2‑hour post‑prandial glucose, fasting glucose, and HbA1c every 3 months. 1, 6