For a type 1 diabetic patient on insulin glargine (Lantus) 14 units daily with a carbohydrate ratio of 1 unit per 18 g carbs, who received dexamethasone 4 mg 16 hours ago and is due for the next Lantus dose, how much should the basal insulin be increased and how should the carb‑to‑insulin ratio be adjusted?

Insulin Adjustment for Type 1 Diabetes After Dexamethasone 4 mg

Increase Lantus from 14 units to 21 units (150% of baseline) tonight, and tighten the carbohydrate ratio from 1:18 to 1:8 for the next 24–48 hours to counteract dexamethasone-induced insulin resistance. 1

Understanding Dexamethasone's Temporal Effects

Dexamethasone causes profound hyperglycemia that peaks 7–9 hours after administration and persists for at least 24 hours, characterized by afternoon and evening glucose elevations. 1, 2 At 16 hours post-dose, you are approaching the peak steroid effect, meaning insulin resistance is near its maximum. 1 The hyperglycemic effect is driven by impaired beta-cell insulin secretion, increased hepatic gluconeogenesis, and marked peripheral insulin resistance at the cellular level—specifically through depletion of insulin receptor substrate-1 (IRS-1) and protein kinase B. 3, 4

Specific Lantus Dosing at 16 Hours Post-Dexamethasone

• Increase Lantus to 21 units tonight (150% of the baseline 14 units), as recommended for patients receiving high-dose dexamethasone (4 mg qualifies as a significant dose requiring aggressive adjustment). 1
• This 50% increase addresses the profound basal insulin resistance induced by dexamethasone, which affects both fasting and between-meal glucose levels. 5, 1
• Maintain this increased dose for at least 24 hours after the dexamethasone administration (until approximately 28 hours post-dose), then begin tapering back toward baseline as glucose normalizes. 1, 2
• For patients with type 1 diabetes on steroids, adding 0.1–0.3 units/kg/day to the usual insulin regimen is standard; in a patient weighing approximately 78 kg (14 units ÷ 0.18 units/kg), this translates to adding 8–23 units, making 21 units (7 units added) a conservative but appropriate increase. 2

Carbohydrate Ratio Adjustment

• Tighten the carbohydrate ratio from 1:18 to 1:8 (representing a 125% increase in mealtime insulin per gram of carbohydrate) for the next 24–48 hours. 1
• This aggressive adjustment is necessary because dexamethasone-induced insulin resistance affects both basal and prandial insulin requirements, often necessitating 40–60% or more increases in prandial and correction insulin. 5
• The 1:8 ratio reflects the 20–25% increase in insulin recommended by guidelines, but given the severity of dexamethasone's effect, starting at 1:8 rather than 1:10 is prudent for a labile type 1 diabetic. 1
• Monitor pre-meal and 2-hour post-meal glucose closely; if post-prandial values consistently exceed 180 mg/dL despite the 1:8 ratio, further tighten to 1:6 or 1:7. 1, 2

Correction Scale Intensification

• Implement a more aggressive correction scale for the next 24–48 hours, using a correction factor of approximately 1 unit per 25 mg/dL above target (compared to the usual 1 unit per 30–50 mg/dL). 1
• Example correction scale for steroid-induced hyperglycemia:
  • Blood glucose 150–175 mg/dL: 1 unit
  • Blood glucose 176–200 mg/dL: 2 units
  • Blood glucose 201–250 mg/dL: 3 units
  • Blood glucose 251–300 mg/dL: 4 units
  • Blood glucose >300 mg/dL: 5 units and call provider 1
• Administer correction insulin every 4–6 hours as needed, focusing on afternoon and evening readings when dexamethasone-induced hyperglycemia peaks. 1, 2

Critical Monitoring Requirements

• Check blood glucose every 4–6 hours for the next 48 hours, with particular attention to afternoon and evening values (4–12 hours post-dexamethasone dose) when hyperglycemia is most pronounced. 1, 2
• Fasting glucose tomorrow morning (approximately 24 hours post-dexamethasone) will guide whether the Lantus increase was adequate; if fasting glucose remains >180 mg/dL, consider increasing Lantus by an additional 2–4 units. 5
• Type 1 diabetes patients are at higher risk for ketoacidosis during steroid-induced hyperglycemia; if glucose exceeds 300 mg/dL with nausea, vomiting, or abdominal pain, check ketones immediately. 5

Tapering Strategy (24–48 Hours Post-Dexamethasone)

• At 24 hours post-dexamethasone, if fasting glucose is <180 mg/dL, begin reducing Lantus back toward baseline by 10–20% (reduce from 21 units to 17–19 units). 2
• At 48 hours post-dexamethasone, the steroid effect is substantially diminished; reduce Lantus to 14–16 units (approximately 50–60% of the increased dose) to prevent hypoglycemia as insulin resistance normalizes. 2
• Return the carbohydrate ratio from 1:8 to approximately 1:10 or 1:12 at 24 hours, then back to 1:18 by 48 hours, representing a 30–40% reduction in mealtime insulin as insulin resistance resolves. 2
• The transition from 24 to 48 hours post-dexamethasone is a high-risk period for hypoglycemia if insulin doses are not appropriately reduced; insulin requirements can decline rapidly once the steroid effect wanes. 1, 2

Special Considerations for Type 1 Diabetes

• Never discontinue basal insulin entirely, even if glucose is well-controlled, as type 1 diabetics lack endogenous insulin production and are at risk for diabetic ketoacidosis. 5, 6
• Labile type 1 diabetes (as noted in this patient) means glucose variability is already high; dexamethasone will exacerbate this, requiring more frequent monitoring and aggressive correction. 5
• If hyperglycemia persists despite increased Lantus, consider adding NPH insulin in the morning (approximately 0.1–0.3 units/kg, or 8–23 units for this patient) in addition to the Lantus to provide additional daytime basal coverage during the steroid effect. 1

Common Pitfalls to Avoid

• The most dangerous error is maintaining the increased insulin doses beyond 24–48 hours, as this creates severe hypoglycemia risk when steroid effects dissipate; 75% of hospitalized patients who experience hypoglycemia have no basal insulin dose adjustment before the next administration. 5, 2
• Do not rely solely on correction insulin without adjusting scheduled basal and prandial doses; sliding-scale insulin as monotherapy is condemned by major diabetes guidelines and leads to dangerous glucose fluctuations. 5, 6
• Avoid using rapid-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk, especially during the tapering phase. 5, 6
• Do not delay prandial insulin adjustments; if pre-meal glucose repeatedly exceeds 180 mg/dL on the tightened carbohydrate ratio, further increase mealtime insulin rather than relying on corrections. 5, 1

Expected Clinical Outcomes

• With appropriate basal-bolus adjustments for steroid effect, approximately 68% of patients achieve mean glucose <140 mg/dL, compared with 38% using inadequate sliding-scale approaches. 5, 6
• Total daily insulin requirements may be 40–60% higher than baseline during the peak steroid effect (24–48 hours post-dose), often reaching 10–15 units per meal after full titration. 5
• Properly implemented basal-bolus therapy does not increase hypoglycemia incidence when correctly applied and appropriately tapered. 5, 6