In an adult with type 1 or type 2 diabetes on insulin glargine (Lantus) 11 U daily and a carbohydrate‑to‑insulin ratio of 1 U per 15 g, who just received 4 mg dexamethasone, how much should the basal insulin dose and carbohydrate coverage be increased?

Adjusting Insulin Lantus and Carbohydrate Coverage After Dexamethasone 4 mg

Increase Lantus by 20–30% (to approximately 13–14 units) and tighten the carbohydrate ratio from 1:15 to approximately 1:10 (or add 40–60% more prandial insulin) to counteract the hyperglycemic effect of dexamethasone. 1

Understanding Dexamethasone-Induced Hyperglycemia

• Dexamethasone is a long-acting glucocorticoid that produces sustained hyperglycemia throughout the day, requiring both increased basal and prandial insulin coverage. 1
• Glucocorticoid therapy typically necessitates 40–60% or more additional insulin beyond baseline requirements, affecting both basal and mealtime doses. 1, 2
• The hyperglycemic effect of dexamethasone persists for approximately 12–24 hours after administration, demanding continuous insulin coverage rather than just peak-time adjustments. 1

Basal Insulin (Lantus) Adjustment

Immediate Dose Increase

• Increase Lantus from 11 units to 13–14 units (approximately 20–30% increase) to provide adequate basal coverage during dexamethasone therapy. 1, 2
• For long-acting glucocorticoids like dexamethasone or continuous glucocorticoid use, long-acting insulin (such as Lantus) is the appropriate basal insulin choice. 1
• This initial increase addresses the baseline insulin resistance induced by the steroid without waiting for glucose patterns to emerge. 1, 2

Titration Protocol

• Monitor fasting glucose daily and increase Lantus by 2 units every 3 days if fasting glucose remains ≥180 mg/dL. 2
• If fasting glucose is 140–179 mg/dL, increase by 2 units every 3 days until reaching the target of 80–130 mg/dL. 2
• If any glucose reading falls <70 mg/dL, immediately reduce Lantus by 10–20% (approximately 1–2 units). 2

Upper Limit Considerations

• When Lantus approaches 0.5 units/kg/day (approximately 35–40 units for most adults) without achieving targets, prioritize adding or intensifying prandial insulin rather than further basal escalation. 2
• Clinical signs 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. 2

Prandial Insulin (Carbohydrate Coverage) Adjustment

Carbohydrate-to-Insulin Ratio Modification

• Tighten the carbohydrate ratio from 1:15 to approximately 1:10 (or 1:12 as an intermediate step), representing a 33–50% increase in prandial insulin per gram of carbohydrate. 1, 2
• This adjustment means that for every 15 grams of carbohydrate previously covered by 1 unit, you now need approximately 1.5 units (using 1:10 ratio). 1, 2
• The 1:10 ratio is a standard starting point for carbohydrate counting, and steroid-induced resistance often requires ratios as tight as 1:8 or 1:6–7 for adequate coverage. 2, 3

Alternative Fixed-Dose Approach

• If carbohydrate counting is not preferred, add 4–6 units of rapid-acting insulin before each meal (or 10% of the current basal dose), then titrate based on 2-hour post-prandial glucose. 2
• Increase each meal dose by 1–2 units every 3 days if 2-hour post-prandial glucose consistently exceeds 180 mg/dL. 2
• Administer rapid-acting insulin 0–15 minutes before meals for optimal post-prandial control. 2

Correction Insulin Protocol

• Add 2 units of rapid-acting insulin for pre-meal glucose >250 mg/dL and 4 units for glucose >350 mg/dL, in addition to the scheduled prandial dose. 2
• These correction doses supplement—not replace—the scheduled carbohydrate coverage. 2

Monitoring Requirements

Glucose Checking Schedule

• Check fasting glucose daily to guide Lantus adjustments. 2
• Measure pre-meal glucose before each meal to calculate correction doses. 2
• Obtain 2-hour post-prandial glucose after each meal to assess adequacy of carbohydrate coverage and guide prandial insulin titration. 2
• Check bedtime glucose to evaluate overall daily pattern. 2

Reassessment Intervals

• Reassess insulin doses every 3 days during active titration while on dexamethasone. 2
• More frequent monitoring (every 2–4 hours) may be needed in the first 24–48 hours after starting dexamethasone to identify patterns. 3

Special Considerations for Dexamethasone

Duration of Effect

• Dexamethasone has a longer duration of action than prednisone, producing sustained hyperglycemia that requires continuous basal and prandial coverage rather than just morning NPH. 1, 3
• Unlike morning prednisone (which peaks 4–8 hours after dosing), dexamethasone maintains insulin resistance throughout the day and night. 1, 3

Dose-Dependent Insulin Requirements

• Higher doses of glucocorticoids require proportionally more insulin; a 4 mg dose of dexamethasone is equivalent to approximately 24–30 mg of prednisone. 1
• For severe hyperglycemia on high-dose steroids, total insulin requirements may reach 0.3–0.5 units/kg/day or higher, split between basal and prandial components. 2

When Dexamethasone Is Discontinued

Rapid Dose Reduction

• Upon stopping dexamethasone, insulin needs may drop by 50–70% within 24–48 hours. 2
• Reduce both Lantus and prandial insulin by 30–40% immediately after the last dexamethasone dose to prevent hypoglycemia. 2, 3
• Return to baseline insulin doses (11 units Lantus and 1:15 carb ratio) within 2–3 days after steroid cessation, monitoring closely for hypoglycemia. 2, 3

Common Pitfalls to Avoid

• Do not delay insulin intensification when starting dexamethasone; proactive dose increases prevent prolonged hyperglycemia and its complications. 1, 2
• Do not rely solely on correction insulin without adjusting scheduled basal and prandial doses; this reactive approach is condemned by major diabetes guidelines. 2
• Never use rapid-acting insulin at bedtime as a sole correction dose, as it markedly raises nocturnal hypoglycemia risk. 2
• Avoid continuing basal insulin escalation beyond 0.5 units/kg/day without addressing post-prandial hyperglycemia, to prevent over-basalization and hypoglycemia. 2
• Do not maintain full steroid-dose insulin requirements after dexamethasone discontinuation; failure to reduce insulin promptly causes severe hypoglycemia. 2, 3

Expected Clinical Outcomes

• With appropriate basal-bolus adjustments for dexamethasone, approximately 68% of patients achieve mean glucose <140 mg/dL, compared with 38% using inadequate sliding-scale approaches. 2
• Properly implemented steroid-adjusted insulin regimens do not increase hypoglycemia incidence compared with under-dosed insulin when titration protocols are followed. 2
• Target glucose range during steroid therapy is 140–180 mg/dL for most patients, with fasting glucose 80–130 mg/dL. 2