A patient on insulin glargine (Lantus) 11 U daily with a carbohydrate‑to‑insulin ratio of 1 U per 15 g carbs and a medium correction factor will receive dexamethasone 4 mg; what should the basal glargine dose, carbohydrate ratio, and correction factor be adjusted to?

Adjusting Insulin Glargine, Carbohydrate Ratio, and Correction Scale for Dexamethasone 4 mg

Increase basal insulin glargine to approximately 15–16 units once daily, tighten the carbohydrate ratio to 1 unit per 10–12 grams of carbohydrate, and use a more aggressive correction scale (1 unit per 30 mg/dL above target instead of the previous medium scale) to counteract the 40–60% increase in insulin requirements caused by dexamethasone 4 mg. 1

Immediate Basal Insulin Adjustment

• Increase Lantus from 11 units to 15–16 units once daily (approximately 35–45% increase) to account for glucocorticoid-induced insulin resistance. 1
• Dexamethasone at 4 mg requires increasing prandial and correction insulin by 40–60% in addition to basal insulin adjustments. 1
• Glucocorticoid therapy can necessitate extraordinary amounts of insulin beyond typical ranges, with careful monitoring and adjustment of all insulin components. 1
• Administer the increased Lantus dose at the usual bedtime to ensure continuous 24-hour basal coverage during the steroid-induced insulin-resistant period. 1

Carbohydrate-to-Insulin Ratio Adjustment

• Tighten the ratio from 1:15 to 1:10–12 grams of carbohydrate to address the marked increase in post-prandial insulin resistance caused by dexamethasone. 1, 2
• Steroid-induced resistance often requires tightening the ratio to 1:8 or even 1:6–7 for lunch and dinner when morning prednisone/dexamethasone is used. 1
• The 1:10 ratio (calculated as 450 ÷ total daily dose) serves as a reasonable starting point, but expect to adjust further based on 2-hour post-prandial glucose readings. 1
• Dexamethasone impairs insulin signaling by depleting insulin receptor substrate-1 (IRS-1) by approximately 75% and protein kinase B (PKB) by approximately 45%, substantially reducing cellular insulin sensitivity. 3

Correction Scale Intensification

• Use an insulin sensitivity factor (ISF) of approximately 1 unit per 30 mg/dL above target (calculated as 1500 ÷ estimated new total daily dose of ~50 units). 1
• For a simplified sliding scale approach: add 2 units for pre-meal glucose >250 mg/dL and 4 units for glucose >350 mg/dL, in addition to scheduled prandial doses. 1
• The "medium" correction scale previously used is insufficient during steroid therapy; expect to use 40–60% more correction insulin than baseline. 1
• Correction doses must supplement—not replace—scheduled basal and prandial insulin. 1

Monitoring Protocol During Steroid Therapy

• Check fasting glucose daily to guide basal insulin titration, targeting 80–130 mg/dL. 1
• Measure pre-meal glucose before each meal to calculate correction doses. 1
• Obtain 2-hour post-prandial glucose after lunch and dinner to assess adequacy of the tightened carbohydrate ratio. 1
• Increase basal insulin by 2 units every 3 days if fasting glucose is 140–179 mg/dL, or by 4 units every 3 days if fasting glucose ≥180 mg/dL. 1
• Increase prandial insulin by 1–2 units every 3 days based on 2-hour post-prandial glucose readings, targeting <180 mg/dL. 1

Mechanism of Dexamethasone-Induced Insulin Resistance

• Dexamethasone decreases both basal and insulin-stimulated glucose uptake by approximately 40–50% in adipocytes, independent of surrounding glucose concentration. 3
• Glucocorticoids reduce insulin binding by approximately 40% and substantially decrease PKB content by approximately 45%, impairing insulin signaling. 3
• Insulin-stimulated PKB phosphorylation is decreased by approximately 40% in dexamethasone-treated cells, further compromising glucose transport. 3
• These effects occur independently of surrounding glucose and insulin levels, necessitating proactive insulin dose increases rather than reactive adjustments. 3

Expected Clinical Outcomes

• With appropriate insulin intensification (40–60% increase across all components), approximately 68% of patients achieve mean glucose <140 mg/dL during steroid therapy. 1
• Total daily insulin requirements may reach 10–15 units per meal after full titration, substantially higher than the pre-steroid baseline. 1
• Properly implemented basal-bolus adjustments for steroid therapy do not increase hypoglycemia incidence when correctly applied. 1

Tapering Insulin as Dexamethasone is Discontinued

• As dexamethasone doses are tapered or stopped, reduce all insulin components proportionally—typically by 40–60%—reflecting the waning steroid effect. 1
• Return to the original Lantus dose of 11 units, carbohydrate ratio of 1:15, and medium correction scale once dexamethasone is fully discontinued and glucose patterns stabilize. 1
• Monitor glucose closely during the taper period, checking at least four times daily to guide dose reductions. 1

Critical Pitfalls to Avoid

• Do not delay insulin intensification when starting dexamethasone 4 mg; the 40–60% increase in requirements begins immediately with steroid initiation. 1
• Never rely solely on correction insulin without adjusting scheduled basal and prandial doses; this reactive approach is condemned by major diabetes guidelines. 1
• Avoid continuing basal insulin escalation beyond 0.5 units/kg/day without addressing post-prandial hyperglycemia with tightened carbohydrate ratios. 1
• Do not use rapid-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk. 1

Hypoglycemia Management

• Treat glucose <70 mg/dL immediately with 15 g of fast-acting carbohydrate, recheck in 15 minutes, and repeat if needed. 1
• If hypoglycemia occurs without an obvious cause, reduce the implicated insulin dose by 10–20% promptly. 1
• Provide comprehensive patient education on hypoglycemia recognition, treatment, and the temporary nature of increased insulin needs during steroid therapy. 1