If the post-meal blood sugar level is constantly too high, i.e. over 10–12 mmol/l regardless of other forms of therapy, mealtime insulin injections should be taken into consideration. However, if the person is obese, the addition of GLP-1 injections to the basal insulin therapy should be the first option. To begin with, mealtime insulin can be taken just for the meal resulting in the highest increase of blood sugar.
Over the years, a person with type 2 diabetes may also accumulate a significant insulin deficiency requiring standard MDI therapy. The principles of MDI therapy are not materially different from those of type 1 diabetes therapy. That said, a person who has developed insulin resistance requires more insulin, in which case the insulin doses are usually bigger than for type 1 diabetes. Metformin and SGLT2 inhibitors are normally used parallel with MDI therapy, provided that there are no contraindications.
MDI therapy involves 1–2 injections of long-acting basal insulin in addition to an injection of rapid-acting mealtime insulin, either per meal or for the meal resulting in the most drastic increase in blood sugar.
The normal required amount of mealtime insulin is 1–4 units of rapid-acting insulin per 10 g of carbohydrates. Nonetheless, the initial doses are small, such as 4 units before a meal. The correct insulin-to-carbohydrate ratio is established by blood sugar tests before and after meals.
After starting mealtime insulin, basal insulin generally needs to be reduced. When going to bed with a good blood sugar level of 6–8 mmol/l, a smaller dose of basal insulin than before is usually sufficient. The appropriate dose of basal insulin is adjusted based on evening-to-morning blood sugar measurements so that the change in blood sugar overnight is at most ± 2–3 mmol/l.