Can I add insulin glargine (glargine) to a regimen of twice‑daily neutral protamine Hagedorn (NPH) insulin and insulin lispro sliding‑scale to reduce or discontinue the sliding‑scale?

Can You Add Insulin Glargine to NPH Twice Daily Plus Lispro Sliding Scale?

No, you should not add insulin glargine to this regimen—instead, you must completely restructure the insulin therapy by discontinuing the sliding-scale lispro monotherapy and transitioning to a proper basal-bolus regimen using glargine as basal insulin with scheduled prandial lispro.

Critical Problems with the Current Regimen

• Sliding-scale insulin as monotherapy is explicitly condemned by all major diabetes guidelines and should be immediately discontinued; it treats hyperglycemia reactively after it occurs rather than preventing it, leading to dangerous glucose fluctuations.1
• Only ≈38% of patients on sliding-scale alone achieve mean glucose <140 mg/dL, versus ≈68% with scheduled basal-bolus therapy, demonstrating the complete inadequacy of this approach.1
• Combining NPH twice daily with glargine once daily creates unnecessary complexity with overlapping basal insulin coverage, increasing hypoglycemia risk without improving glycemic control—this approach is not supported by clinical guidelines.2

The Correct Approach: Transition to Basal-Bolus Therapy

Step 1: Replace NPH with Glargine as Basal Insulin

• Discontinue NPH insulin completely and initiate insulin glargine at 80% of the total daily NPH dose given once daily at the same time each day (bedtime or dinnertime).3
• For example, if the patient is on NPH 20 units twice daily (40 units total), start glargine at 32 units once daily.3
• Glargine provides more steady 24-hour basal coverage with lower nocturnal hypoglycemia risk compared to NPH, which has pronounced peaks.4, 5, 6

Step 2: Convert Sliding-Scale Lispro to Scheduled Prandial Insulin

• Discontinue sliding-scale lispro as the sole regimen and initiate scheduled prandial lispro at 4 units before each of the three largest meals (or 10% of the basal dose).1, 7
• Administer lispro 0-15 minutes before meals for optimal postprandial glucose control.1, 7
• Correction insulin should supplement—not replace—scheduled prandial doses: add 2 units for pre-meal glucose >250 mg/dL and 4 units for >350 mg/dL.1, 7

Step 3: Systematic Titration Protocol

Basal Insulin (Glargine) Titration:

• Increase by 2 units every 3 days if fasting glucose is 140-179 mg/dL.1, 7
• Increase by 4 units every 3 days if fasting glucose is ≥180 mg/dL.1, 7
• Target fasting glucose 80-130 mg/dL.1, 7
• If hypoglycemia (<70 mg/dL) occurs, reduce the dose by 10-20% immediately.1, 7

Prandial Insulin (Lispro) Titration:

• Adjust each meal dose by 1-2 units (≈10-15%) every 3 days based on 2-hour postprandial glucose.1, 7
• Target postprandial glucose <180 mg/dL.1, 7

Why Not Add Glargine to NPH?

• Overlapping two different basal insulins (NPH + glargine) is not recommended by diabetes guidelines and creates unnecessary complexity with increased hypoglycemia risk.2
• NPH has a pronounced peak at 4-12 hours, while glargine provides peakless 24-hour coverage—combining them results in unpredictable insulin action profiles.4, 8
• Studies demonstrate that switching from NPH to glargine (not adding glargine to NPH) results in lower fasting glucose, reduced glucose variability, and fewer nocturnal hypoglycemic episodes.4, 5, 6

Monitoring Requirements

• Daily fasting glucose checks during titration to guide basal insulin adjustments.1, 7
• Pre-meal glucose before each meal to calculate correction doses.1, 7
• 2-hour postprandial glucose after each meal to assess prandial adequacy.1, 7
• HbA1c every 3 months during intensive titration.1, 7

Expected Clinical Outcomes

• With properly implemented basal-bolus therapy using glargine and scheduled lispro, ≈68% of patients achieve mean glucose <140 mg/dL versus ≈38% with sliding-scale alone.1, 7
• HbA1c reductions of 2-3% are achievable over 3-6 months with intensive titration.1, 7
• Glargine demonstrates significantly lower nocturnal hypoglycemia rates compared to NPH in multiple randomized trials.4, 5, 6

Critical Pitfalls to Avoid

• Never use sliding-scale insulin as monotherapy—this reactive approach is condemned by all major diabetes guidelines.1, 7
• Do not combine NPH and glargine as overlapping basal insulins; choose one basal insulin and optimize it.2
• Do not delay adding scheduled prandial insulin when transitioning from sliding-scale; correction doses must supplement, not replace, scheduled insulin.1, 7
• Never give rapid-acting insulin at bedtime as a sole correction dose, as this markedly raises nocturnal hypoglycemia risk.1, 7

Alternative Consideration: If Cost Is the Primary Concern

• If insurance does not cover glargine and cost is prohibitive, continue NPH but switch to twice-daily dosing (before breakfast and at bedtime) combined with scheduled prandial lispro at meals—this is superior to adding glargine to NPH.2
• NPH twice daily can achieve equivalent glycemic control to glargine when dosed appropriately, though with higher nocturnal hypoglycemia risk.2, 5