Individuals with type 2 diabetes mellitus (T2DM) spend between 5 and 10 years with elevated hemoglobin A1c (HbA1c) before initiation of insulin.1 Once the basal insulin is initiated, the patient can go years with only adjustment of the basal insulin, resulting in over-basalization. In general, the total daily dose (TDD) of insulin should be composed of about 50% basal “background” insulin and 50% bolus “meal” insulin. When the fasting glucose readings are on target but HbA1c is still above the mutually set goal range, postprandial readings need to be evaluated.
This article focuses on initiating and titrating bolus insulin in nonpregnant patients with T2DM. Before initiation of bolus insulin, it is important for the patient to be actively engaged with a diabetes educator for diabetes self-management education and support (DSME/S), including the understanding of the correct use of insulin, carbohydrate counting, and increasing physical activities. Ensuring the correct technique of insulin administration and self-monitoring of blood glucose (SMBG) is critical. A knowledge deficit of carbohydrate information can lead to uncontrolled blood glucose (BG). The authors have encountered numerous times when patients were drinking sugary beverages or consuming large amounts of “healthy” food without realizing the carbohydrate content. Therefore, treatment in concert with a registered dietitian and certified diabetes educator is highly recommended.
Initiation of Bolus Insulin
There are 3 options of postprandial coverage with bolus insulin when a patient is taking basal insulin: basal plus, basal-bolus, or premix insulin. A possible fourth option for postprandial coverage is to add glucagon-like peptide-1 receptor agonist (GLP-1 RA), an injectable noninsulin antihyperglycemic agent, which has shown noninferior efficacy to adding bolus insulin and a favorable effect on weight with less risk of hypoglycemia.2-5 Although it can be expensive, combining GLP-1 RA to basal insulin results in lowering HbA1c of 0.66 up to 1.74% (or lowering mmol/mol of 7 up to 19) from the baseline.6 However, adding bolus insulin may be the only option to avoid glucotoxicity and prevent further diabetes complications when the HbA1c level is well above the goal range. It is usually recommended to discontinue sulfonylurea when bolus insulin is added due to the β-cell exhaustion with advancing natural history of diabetes.7,8
Method 1: Basal Plus
The health care provider (HCP) needs to consider whether the patient is over-basalized when the HbAlc and postprandial BG readings are still not at goal despite careful titration of basal insulin dose to > 0.5 U/kg/d.9 This is the time to discuss with the patient the coverage of mealtime glucose excursions. In the basal plus regimen, the prescribing provider may add 1 bolus insulin injection for the meal with the highest amount of carbohydrates or add 2 bolus injections for the most and second most meals with carbohydrates. Multiple types of bolus insulin are available in the current U.S. market (Table 1).
There are 2 ways to add bolus insulin: fixed and flexible. In the fixed regimen, the patient will take the same amount of bolus insulin regardless of premeal BG readings and carbohydrate content of the food. The authors recommend adding bolus insulin of about 4 to 6 units once or twice a day with meals, depending on the number of meals a day, carbohydrate content of the meal, current and desired degree of diabetes control, and physical activities. Another way to calculate a bolus insulin dose is to start at 0.1 U/kg if adding to the basal insulin.10 Flexible regimen allows various bolus doses based on premeal BG, carbohydrate intake, and activities. Information on this regimen, will be discussed more later.
Patient Cases
Tables 2 and 3 describe 2 patient cases. For example, patient 1 weighs 80 kg. If the prescribing HCP and patient decide to add only 1 bolus to the largest carbohydrate meal at dinnertime, then the patient may take 8 units (80 kg × 0.1 U/kg/meal = 8 units for meal). The patient’s current insulin dose, medical comorbidities, current diabetes control status, living situations, and overall cognition also should be considered.
Imagine patient 1 is taking 14 units daily of a long-acting insulin (LAI). If the patient is taking a fairly low dose of LAI, has multiple comorbidities, recent BG log/HgAlc, and lives alone but demonstrates good cognition to follow instructions, the prescriber may consider adding the bolus insulin of 4 units for dinner; thus, the bolus dose is about one-third of total basal insulin dose. However, if the patient is on 40 units of LAI and has symptoms of hyperglycemia, 6 to 8 units for the dinner is reasonable. An important point to convey to this patient is to make sure there is carbohydrate consistency. The patient’s premeal BG was 137 mg/dL (7.6 mmol/L) on Monday, but it rose significantly to 313 mg/dL (17.4 mmol/L) after dinner. On Wednesday, the patient’s premeal BG prior to dinner was 150 mg/dL (8.3 mmol/L); it rose to 202 mg/dL (11.2 mmol/L) after dinner, which is high but not as high as on Monday.
Multiple factors may affect this variability; for example, on Monday the patient may have consumed more than the usual amount of carbohydrates for dinner, forgot to take oral medication for dinner, or missed his/her usual after-dinner walk. Or simply, the patient may have eaten a lot less than the usual amount of carbohydrates, walked the neighborhood, or vacuumed the entire house after dinner on Wednesday. Thus, it is imperative to carefully assess the patient’s lifestyle and recommend carbohydrate consistency at each meal.
