How to start insulin
When first prescribing insulin for a person with Type 2 diabetes, doctors generally start with a single daily injection of long-acting insulin. Determining what dose of insulin to begin with can be done in different ways. One option is to choose a starting dose based on a person’s weight. Eventually, many people with Type 2 diabetes will require 1–2 units of insulin for every kilogram of body weight; that is, an 80-kilogram (175-pound) person will require at least 80 units of insulin each day. To start, however, your doctor may begin by prescribing 0.15 units of insulin per kilogram. For an 80-kilogram person, this would be 12 units.
Another option is simply to start with 10 units of insulin, a large enough dose to decrease blood glucose levels for most people but not so large that it is likely to cause hypoglycemia. The dose can then be increased every 3–7 days based on fasting blood glucose values. A morning blood glucose reading of 80–100 mg/dl is ideal, so with numbers that fall in this range, you would not make any changes. If your morning blood glucose readings were under 80 mg/dl, you would decrease your insulin dose by 2 units. Most people, however, will need to increase their dose of insulin above the initial level. It is generally safe to adjust one’s basal insulin according to this scale.
Most doctors initially recommend taking insulin in the evening, since this helps reduce a person’s fasting blood glucose level the next morning. However, one problem with taking NPH insulin at bedtime is that it often peaks in the middle of the night, increasing the possibility of hypoglycemia during sleep. Since insulin glargine and insulin detemir do not have a significant peak of action, it is safer to take one of these at bedtime. Depending on a person’s blood glucose trends or personal preferences, basal insulin can also be taken in the morning instead of at bedtime.
One common error made by doctors is to focus too much on normalizing the fasting morning blood glucose level without considering the importance of the bedtime blood glucose level. For example, a person might take 40 units of insulin glargine at bedtime and have an optimal fasting blood glucose level of 110 mg/dl in the morning. However, this person could have a bedtime blood glucose level in the 300’s, which indicates the need to take insulin at dinner (often called “covering” the meal). So although his fasting blood glucose level is fine, this person will still have an HbA1c level greater than 9%. This is why it is important not to rely only on fasting blood glucose levels, but to also use the HbA1c level and, if necessary, blood glucose readings throughout the day to guide treatment.
If after three months of using long-acting insulin alone the HbA1c level is still above 7%, then using Regular or rapid-acting insulin to cover meals will be necessary. Mealtime insulin can initially be given at the largest meal of the day, which is dinner for most Americans. A simple approach for starting mealtime insulin is to decrease the long-acting insulin dose by 10% and take the difference as rapid-acting insulin at dinnertime. For example, if you previously took 20 units of glargine at bedtime, you would take 2 units of aspart, lispro, or glulisine at dinner and 18 units of glargine before bed.
An important concept in insulin therapy is taking “correction doses” of insulin. This means taking extra rapid-acting insulin before a meal to correct for high blood glucose. A common correction dose is 2 extra units of insulin for a premeal blood glucose level above 150 mg/dl; even more will be needed if the level is above 200. Although there is a large range of appropriate correction doses, here is an example of a typical scale. Correction doses can significantly impact blood glucose levels. For example, if you generally take 6 units of insulin aspart with lunch but your blood glucose level before lunch is 250 mg/dl, your usual 6 units will not adequately lower both the current high blood glucose and the anticipated rise from lunch. If you take 4 additional units of insulin, the correction dose will cover your premeal high glucose and the 6 units will cover your meal. Although this system can take a few weeks to adjust to, most people find it rewarding because they can take action to lower their high blood glucose as soon as they know about it, rather than letting it remain high throughout the day.