Am Fam Physician. 2004;69(2):433
To achieve a hemoglobin A1c level of 7 percent or less, many patients with diabetes require insulin therapy. Citing significantly improved glycemic control, DeWitt and Dugdale recommend the addition of an intermediate- to long-acting insulin at bedtime in patients taking oral agents for type 2 diabetes. With the development of new basal and prandial insulins, physicians and patients have more options and a chance for added dosing flexibility. When the A1c level is higher than 9 percent, a patient is unlikely to achieve the American Diabetes Association goal of an A1c level less than 7 percent using only oral medications. Combining daytime metformin with bedtime neutral protamine Hagedorn (NPH) appears to result in better glucose control, less weight gain, and fewer episodes of hypoglycemia than the use of NPH/sulfonylurea, metformin/sulfonylurea, or NPH alone.
| Starting basal insulin (bedtime NPH or glargine): use an initial dose of 10 to 20 U or 0.1 to 0.2 U per kg (a higher dose can be used in poorly controlled patients). |
| Adjusting basal insulin: increase the dose by 4 U if fasting CBG level is higher than 140 mg per dL (7.8 mmol per L) on three consecutive measures or by 2 U if fasting CBG level is 110 to 140 mg per dL (6.1 to 7.8 mmol per L) on three consecutive measures. |
| Most patients with type 2 diabetes need a total daily dosage of 1 to 1.2 U per kg to achieve an A1c level of less than 7 percent (basal dose, 0.5 to 0.6 U per kg per day). |
| Converting from an existing regimen: divide total daily insulin need by two and use that as the basal dose (some experts recommend decreasing the starting basal dose by 20 percent to decrease the risk of hypoglycemia). Alternatively, in a patient already taking NPH or ultralente who is being switched to insulin glargine, use approximately 80 percent of the NPH or ultralente dose as glargine. |
A recommended starting dose is 10 to 20 U of NPH administered at 9 p.m., but patients with type 2 diabetes often require high doses of insulin (see accompanying table). Insulin glargine may produce lower fasting glucose control and better post-dinner control. Prandial insulin can be used to achieve better control after the dinner meal.
Although too complex for some patients, an understanding of the carbohydrate content of a meal allows patients to adjust their prandial dose. Each 10 to 15 g of carbohydrate requires 1 U of insulin (i.e., regular, lispro, or aspart). In addition, patients should allocate 1 to 2 U for every 50 mg per dL blood sugar increment over a threshold of 150 mg per dL.
In patients requiring steroids, the authors recommend more frequent monitoring, and the use of prandial agents such as NPH or glargine may be necessary if fasting blood sugar levels are consistently above the recommended level of 110 mg per dL (6.1 mmol per L).