What initial dose of insulin glargine should be given to a 70‑kg adult receiving peripheral parenteral nutrition with 5% dextrose in lactated Ringer's (D5LR)?

Insulin Glargine Dosing for Patients Receiving Peripheral Parenteral Nutrition with D5LR

For a 70-kg adult receiving peripheral parenteral nutrition (PPN) with 5% dextrose in lactated Ringer's (D5LR), initiate insulin glargine at approximately 10 units once daily, representing the basal component of a basal-bolus regimen, with additional nutritional insulin coverage required to address the continuous carbohydrate load from the dextrose infusion.

Initial Basal Insulin Dosing

• Start insulin glargine at 10 units once daily (approximately 0.1–0.2 units/kg for a 70-kg patient) as the foundational basal insulin dose, administered at the same time each day 1, 2.
• This conservative starting dose minimizes hypoglycemia risk while establishing baseline glycemic control in patients who may be insulin-naïve or at higher risk due to acute illness 1, 3.
• The basal insulin component should represent approximately 50% of the total daily insulin requirement, with the remainder allocated to nutritional/prandial coverage 1, 4.

Nutritional Insulin Coverage for Continuous Dextrose

• D5LR provides a continuous carbohydrate load that requires scheduled nutritional insulin in addition to basal insulin; basal insulin alone is insufficient 4, 5.
• Calculate the carbohydrate content of the D5LR infusion: a typical D5 solution contains approximately 50 grams of dextrose per liter, and the infusion rate determines total carbohydrate delivery 4.
• Administer regular insulin every 6 hours OR rapid-acting insulin (lispro/aspart) every 4 hours to cover the continuous nutritional load, starting at approximately 1 unit per 10–15 grams of carbohydrate in the infusion 1, 4.
• For example, if the patient receives 2 liters of D5LR over 24 hours (≈100 grams carbohydrate), allocate approximately 7–10 units total as nutritional insulin, divided into scheduled doses throughout the day 4.

Titration Protocol

Basal Insulin (Glargine) Adjustment

• Increase glargine by 2 units every 3 days if fasting glucose is 140–179 mg/dL 1, 2.
• Increase glargine by 4 units every 3 days if fasting glucose is ≥180 mg/dL 1, 2.
• Target fasting glucose: 80–130 mg/dL 1, 2.
• Reduce the dose by 10–20% immediately if any unexplained hypoglycemia (<70 mg/dL) occurs 1, 2.

Nutritional Insulin Adjustment

• Titrate nutritional insulin based on glucose patterns throughout the day, targeting glucose <180 mg/dL 1, 5.
• If glucose consistently exceeds 180 mg/dL despite scheduled nutritional insulin, increase the nutritional component by 1–2 units per dose every 3 days 1.

Monitoring Requirements

• Check point-of-care glucose every 4–6 hours initially for patients receiving continuous nutritional support (PPN with dextrose) 1, 4, 5.
• Daily fasting glucose checks are essential to guide basal insulin titration 1, 2.
• Continue basal insulin even if PPN is temporarily interrupted, as basal insulin suppresses hepatic glucose production independent of nutritional intake 1, 5.

Special Considerations for High-Risk Patients

• For elderly patients (>65 years), those with renal impairment (eGFR <60 mL/min), or poor oral intake, start with a lower dose of 0.1–0.25 units/kg/day (approximately 7–17.5 units for a 70-kg patient) to reduce hypoglycemia risk 1, 3.
• For patients with CKD Stage 5, reduce the total daily insulin dose by 50% for type 2 diabetes or 35–40% for type 1 diabetes 1.
• For hospitalized patients on high-dose home insulin (≥0.6 units/kg/day), reduce the total daily dose by 20% upon admission to prevent hypoglycemia 1.

Critical Threshold for Basal Insulin Escalation

• When basal insulin approaches 0.5–1.0 units/kg/day (approximately 35–70 units for a 70-kg patient) without achieving glycemic targets, intensify nutritional insulin coverage rather than further escalating basal insulin to avoid "over-basalization" 1, 4.
• Clinical signals of over-basalization include: basal dose >0.5 units/kg/day, bedtime-to-morning glucose differential ≥50 mg/dL, hypoglycemia episodes, and high glucose variability 1.

Timing and Administration

• Administer the first dose of glargine 1–2 hours BEFORE discontinuing any IV insulin infusion to ensure adequate overlap and prevent rebound hyperglycemia 4.
• Inject glargine subcutaneously into the abdominal area, thigh, or deltoid, rotating injection sites within the same region to reduce lipodystrophy risk 2.
• Administer glargine at the same time each day; the preferred time is 20:00 hours (8 PM) to align with transition protocols, though any consistent time is acceptable 6, 2.

Common Pitfalls to Avoid

• Never discontinue basal insulin completely when PPN is temporarily interrupted, as this can precipitate hyperglycemia and ketosis in insulin-dependent patients 1, 4, 5.
• Do not rely solely on correction (sliding-scale) insulin without scheduled basal and nutritional insulin; this reactive approach is condemned by major diabetes guidelines and leads to dangerous glucose fluctuations 1, 5.
• Never use rapid-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk 1, 5.
• Do not forget nutritional insulin coverage when the patient continues receiving dextrose-containing solutions; the continuous carbohydrate load requires scheduled insulin, not just basal coverage 4, 5.

Expected Clinical Outcomes

• With properly implemented basal-bolus therapy, approximately 68% of patients achieve mean glucose <140 mg/dL, compared with only 38% using sliding-scale insulin alone 1.
• Basal-bolus regimens do not increase hypoglycemia incidence when correctly applied versus inadequate sliding-scale approaches 1.
• Target glucose range for non-critically ill hospitalized patients is 140–180 mg/dL 1, 5.