Subcutaneous Insulin Dosing and Sliding Scale Recommendations

Sliding scale insulin (SSI) as monotherapy should be immediately discontinued and replaced with a scheduled basal-bolus insulin regimen for hospitalized patients with diabetes.

Sliding scale insulin alone is explicitly condemned by all major diabetes guidelines and consistently shown to be inferior to scheduled insulin regimens 1, 2. SSI treats hyperglycemia reactively after it occurs rather than preventing it, leading to dangerous glucose fluctuations that exacerbate both hyper- and hypoglycemia 2. Randomized trials demonstrate that basal-bolus insulin achieves glycemic control (mean blood glucose <140 mg/dL) in 68% of patients versus only 38% with SSI alone, with reduced complications including postoperative wound infection and acute renal failure 2.

Initial Insulin Dosing for Hospitalized Patients

For insulin-naive or low-dose insulin patients:

Start with 0.3-0.5 units/kg/day total daily dose (TDD) 1, 2
Divide as 50% basal insulin (given once daily) and 50% prandial insulin (divided before meals) 1, 2
Example: For a 70 kg patient = 21-35 units TDD → 10.5-17.5 units basal + 10.5-17.5 units prandial (split across 3 meals)

For patients on high-dose home insulin (≥0.6 units/kg/day):

Reduce total daily dose by 20% upon hospitalization to prevent hypoglycemia 1, 3, 2

For high-risk patients (elderly >65 years, renal failure, poor oral intake):

Use lower doses of 0.1-0.25 units/kg/day 1, 3, 2

Basal Insulin Titration Algorithm

Target fasting plasma glucose: 80-130 mg/dL 1, 3

Titration schedule (adjust every 3 days):

If fasting glucose ≥180 mg/dL: Increase basal insulin by 4 units 1, 3
If fasting glucose 140-179 mg/dL: Increase basal insulin by 2 units 1, 3
If fasting glucose <80 mg/dL (more than 2 readings per week): Decrease by 2 units 3
If hypoglycemia occurs: Reduce dose by 10-20% immediately 1, 3

Critical threshold: When basal insulin exceeds 0.5 units/kg/day and approaches 1.0 units/kg/day, stop escalating basal insulin and add prandial insulin instead 1, 3. Continuing to increase basal insulin beyond this threshold leads to "overbasalization" with increased hypoglycemia risk and suboptimal control 1, 3.

Prandial (Bolus) Insulin Dosing

When to add prandial insulin:

Basal insulin dose exceeds 0.5 units/kg/day without achieving glycemic targets 1, 3
Fasting glucose controlled but HbA1c remains elevated after 3-6 months 1, 3
Significant postprandial glucose excursions (>180 mg/dL) 3

Initial prandial insulin dose:

Start with 4 units of rapid-acting insulin before the largest meal 1, 3
OR use 10% of current basal dose 1, 3
Titrate by 1-2 units or 10-15% every 3 days based on 2-hour postprandial glucose readings 1, 3

Carbohydrate coverage:

Common starting ratio: 1 unit per 10-15 grams of carbohydrate 3
Formula: 500 ÷ TDD (for regular insulin) or 450 ÷ TDD (for rapid-acting analogs) 3

Correction (Supplemental) Insulin

Correction insulin should supplement—not replace—scheduled basal-bolus insulin 1, 2.

Insulin sensitivity factor (ISF) calculation:

1500 ÷ Total Daily Dose = mg/dL drop per 1 unit of insulin 3
Example: If TDD = 50 units → ISF = 30 (each unit lowers glucose by ~30 mg/dL)

Correction dose formula:

(Current glucose - Target glucose) ÷ ISF 3
Administer with rapid-acting insulin before meals or every 6 hours 1

Simplified correction scale (if ISF calculation unavailable):

Premeal glucose >250 mg/dL: Give 2 units rapid-acting insulin 2
Premeal glucose >350 mg/dL: Give 4 units rapid-acting insulin 2

If correction doses are frequently required, increase the scheduled basal or prandial insulin doses accordingly 2.

Special Clinical Situations

Patients on glucocorticoids:

Add 0.1-0.3 units/kg/day of basal insulin to usual regimen 3
For higher steroid doses, increase prandial and correction insulin by 40-60% or more 1, 3
Administer NPH insulin concomitantly with intermediate-acting steroids (peaks 4-6 hours after administration) 1

Patients on enteral/parenteral nutrition:

Calculate insulin as 1 unit per 10-15 grams of carbohydrate in formula 1
Give NPH insulin every 8-12 hours to cover nutritional component 1
Continue basal insulin in type 1 diabetes even if feedings discontinued 1
Start dextrose infusion immediately if enteral nutrition interrupted to prevent hypoglycemia 1

Perioperative patients:

Reduce insulin dose by approximately 25% the evening before surgery 3

Type-Specific Dosing

Type 1 Diabetes:

Total daily insulin: 0.4-1.0 units/kg/day (typical: 0.5 units/kg/day) 1, 3, 4
Split as 40-60% basal and 50-60% prandial 1, 3
Must use concomitantly with short-acting insulin—basal insulin alone is insufficient 4, 5

Type 2 Diabetes (insulin-naive):

Start with 10 units once daily OR 0.1-0.2 units/kg/day of basal insulin 1, 3, 4
For severe hyperglycemia (glucose ≥300-350 mg/dL, HbA1c ≥10-12% with symptoms): Start basal-bolus immediately at 0.3-0.5 units/kg/day TDD 1, 3

Insulin Administration Guidelines

Timing and technique:

Administer basal insulin at the same time each day 3, 4
Give rapid-acting insulin 0-15 minutes before meals 3, 5
Inject subcutaneously into abdomen, thigh, or deltoid 4
Rotate injection sites within same region to reduce lipodystrophy risk 4

Critical safety points:

Never dilute or mix insulin glargine with other insulins due to low pH 3, 4
Do not administer intravenously or via insulin pump 4
Never share pens, syringes, or needles between patients 4
Use shortest needles (4-mm pen, 6-mm syringe) to avoid intramuscular injection 5

Monitoring Requirements

Daily fasting blood glucose during titration phase 1, 3
Pre-meal and 2-hour postprandial glucose to guide prandial insulin adjustments 3
HbA1c every 3 months during intensive titration 3
Assess insulin dose adequacy at every clinical visit, looking for signs of overbasalization 1, 3

Foundation Therapy: Continue Metformin

Metformin should be continued at maximum tolerated dose (up to 2000-2550 mg daily) when adding insulin therapy unless contraindicated 1, 3. This combination provides superior glycemic control with reduced insulin requirements, less weight gain, and decreased hypoglycemia compared to insulin alone 1, 3.

Common Pitfalls to Avoid

Never use SSI as monotherapy for hospitalized patients with established diabetes 1, 2
Never delay insulin initiation in patients not achieving glycemic goals with oral medications 3
Never continue escalating basal insulin beyond 0.5-1.0 units/kg/day without addressing postprandial hyperglycemia—this causes overbasalization 1, 3
Never abruptly discontinue oral medications when starting insulin (except sulfonylureas when advancing beyond basal-only) 3
Never inject into areas of lipodystrophy—this distorts insulin absorption 4, 5
75% of hospitalized patients who experienced hypoglycemia had no basal insulin dose adjustment before the next administration—adjust doses promptly 3

Signs of Overbasalization (When to Stop Increasing Basal Insulin)

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

When these signs appear, add prandial insulin or GLP-1 receptor agonist rather than continuing to escalate basal insulin 1, 3.

What is the recommended subcutaneous insulin dosing regimen, including sliding scale (blood glucose level-based dosing), for a patient with diabetes, considering their medical history and current medications, including oral hypoglycemic agents?

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