For a patient on NPH insulin 5 units AM and 5 units at bedtime, metformin 750 mg twice daily, and Novolin R (regular insulin) 6 units before each meal with a sliding‑scale of 1 unit for glucose 200–250 mg/dL, and recent glucose readings of 158 mg/dL at 6 AM, 79 mg/dL at 8:35 PM, 191 mg/dL at 3 PM, 305 mg/dL at noon, 199 mg/dL at 5 AM, and 126 mg/dL the night before, how should the insulin doses be adjusted?

Insulin Dose Adjustment Recommendation

Reduce the bedtime NPH insulin dose by 1 unit (from 5 units to 4 units at bedtime) to address the nocturnal hypoglycemia (79 mg/dL at 8:35 PM), and increase the noon Novolin R dose by 2 units (from 6 units to 8 units before lunch) to address the severe postprandial hyperglycemia (305 mg/dL at noon). 1

Analysis of Glucose Pattern

Your patient's glucose readings reveal two distinct problems:

• Nocturnal hypoglycemia: The 79 mg/dL reading at 8:35 PM indicates the bedtime NPH is causing excessive glucose lowering overnight
• Severe postprandial hyperglycemia at lunch: The 305 mg/dL at noon represents inadequate prandial insulin coverage for the midday meal
• Acceptable morning fasting glucose: The 158 mg/dL at 6 AM is reasonable, though could be optimized further once hypoglycemia is resolved
• Afternoon hyperglycemia: The 191 mg/dL at 3 PM suggests the lunch insulin dose is insufficient

Rationale for Dose Adjustments

Bedtime NPH Reduction

The 2025 ADA Standards of Care explicitly state: "For hypoglycemia: determine cause; if no clear reason, lower dose by 10-20%" 1. A 1-unit reduction from 5 units represents a 20% decrease, which is appropriate for addressing the documented nocturnal hypoglycemia. The bedtime NPH peaks 4-12 hours after injection 2, meaning the 8:35 PM low glucose (approximately 14-15 hours after the morning dose and 2-3 hours after the bedtime dose) is likely caused by the evening NPH dose.

Noon Prandial Insulin Increase

The 305 mg/dL reading at noon—occurring approximately 2-3 hours after the breakfast meal—represents severe postprandial hyperglycemia. According to ADA guidelines, when A1C remains above goal with basal insulin, "increase dose by 1-2 units insulin dose or 10-15%" for prandial insulin 1. A 2-unit increase (from 6 to 8 units) represents a 33% increase, which is justified given the glucose level exceeds 300 mg/dL—a threshold the guidelines identify as requiring prompt intervention 1.

Important Caveats

Hypoglycemia Takes Priority

Addressing hypoglycemia must be the first priority before intensifying other insulin doses 1. The nocturnal low of 79 mg/dL poses immediate risk for severe hypoglycemia, which can lead to loss of consciousness, seizures, or death 3. The ADA guidelines emphasize that hypoglycemia management supersedes glycemic targets.

NPH Pharmacokinetics

NPH insulin has a peak action 4-12 hours after injection with duration up to 24 hours 2. The morning NPH dose (5 units at 5-6 AM) would peak around 9 AM-6 PM, potentially contributing to the afternoon glucose of 191 mg/dL being relatively controlled. However, the bedtime dose is clearly excessive for overnight needs.

Monitoring Plan

After making these adjustments:

• Check fasting glucose daily to ensure the bedtime NPH reduction doesn't cause excessive morning hyperglycemia
• Check pre-lunch and 2-hour post-lunch glucose for 3-5 days to assess the increased noon Novolin R dose
• Continue checking bedtime glucose to confirm resolution of nocturnal hypoglycemia
• If fasting glucose rises above 180 mg/dL consistently, consider increasing morning NPH by 1 unit 1

Alternative Consideration: Switching to Twice-Daily NPH

If glucose control remains suboptimal after these adjustments, the ADA guidelines recommend "consider converting to twice-daily NPH plan" when adding prandial insulin to bedtime NPH 1. This would involve:

• Total NPH dose = 80% of current bedtime NPH (approximately 8 units total)
• 2/3 given before breakfast (approximately 5 units)
• 1/3 given before dinner (approximately 3 units)
• This can be mixed with the Novolin R in the same syringe 3

However, this conversion should wait until the current hypoglycemia is resolved and you've optimized the simpler regimen first.

Why Not Adjust Other Doses?

• Morning NPH (5 units AM): The afternoon glucose of 191 mg/dL and evening glucose of 126 mg/dL suggest this dose is appropriate. The morning fasting glucose of 158 mg/dL is acceptable given the need to avoid nocturnal hypoglycemia.
• Breakfast and dinner Novolin R (6 units each): Insufficient data to assess these doses. The 3 PM reading (191 mg/dL) occurs too late to reflect breakfast insulin effect, and no post-dinner glucose is provided.

The metformin 750 mg BID should be continued unchanged as it provides complementary glucose-lowering without increasing hypoglycemia risk and helps limit weight gain 4.