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Rapid-acting insulin

Now that we have gone over how to keep glucose levels steady with basal insulin, let’s talk about the use of rapid acting insulin for carb coverage and correction bolues. A bolus is the term used for the administration of a medication to raise its content in the blood. In the case of diabetes, we give a bolus of rapid-acting insulin to cover the carbs in a snack/meal, or to bring down a high blood sugar level. Current rapid insulins available include Humalog, Novolog, Fiasp, and Apidra. Boluses can be given through injections or through insulin pump therapy.

Most meals will raise blood glucose levels for 2-3 hours. Rapid insulins provide fair coverage for these meals and can lower blood glucose levels more quickly than previously used insulins (such as regular insulin). They begin working in 10-20 minutes of administration, peak in 1.5-2hrs, and have a total duration of 4-5 hours. Because of this, rapid insulin given 15-20 minutes before a meal will begin working just as the meal is raising the blood glucose level. This allows for less of a glucose peak and more stable post-meal blood sugars. Timing of insulin delivery is very important! For the best results, make sure to bolus 15-20 minutes before your meals!

Sometimes people are given set doses of rapid insulin. For example, their clinician will instruct them to take 10 units three times a day 15-20min before a meal. However, the best and most accurate way to control your glucose level is by carbohydrate counting. This involves totaling the amount of carbs being eaten and then dividing it by what we call a “carb factor”. This carb factor is your total insulin to carb ratio (ex. 15 carbs=1 insulin unit), which is determined by your clinician based on your total daily dose (TDD) of insulin. Once the carb factor has been determined, it allows for much more flexibility with food choices than set dosages do. Think about it, the purpose of giving rapid acting insulin is to cover your food. If you don’t eat the same food with every meal why would you give the same insulin dose?

Although a regimen of set dosages is much easier for someone to remember, it comes with obvious restrictions and any added spontaneity in food choices can lead to a blood sugar roller coaster. Carb counting with an accurate carb factor can allow freedom of food choices with better blood glucose control. I therefore always encourage carb counting because although it is more work in the beginning it eventually allows for more freedom and less disease burden. An accurate carb factor with rapid acting insulin will take your blood glucose level from your target before a meal to a blood glucose level of 180mg/dl or less 2-hrs after a meal. It will then bring you back down to your target glucose level within 3-4 hrs post-prandial. An accurate carb factor will decrease the amount of correction insulin needed by allowing people to be proactive about their blood sugars (avoiding highs) instead of reacting to high blood sugars with a “sliding scale”.

Even with great control and an accurate carb factor, high glucose levels cannot always be avoided so your clinician will additionally give you a “correction factor”, also based on your TDD. This correction factor is how many points your blood sugar will drop with one unit of insulin (ex. 1 unit=50mg/dl drop). When giving a correction with rapid insulin it is important to remember the duration time of the insulin. Do not give a correction bolus within 4hrs of a previous bolus. When this is done it is called “insulin stacking” and can lead to significant lows. Also, lows can occur with rapid acting insulin due to carb counting errors, an overlap of carb boluses, increased physical activity, or excess basal insulin. Be sure to document these lows and ask your clinician for help with investigating why they may have occurred.

Most insulin pumps are equipped with a bolus calculator which will do these carb and correction calculations for you, however if you are on multiple daily injections, on set dosages, and want better control, the calculations are simple. Ask your clinician to explain them to you! Trust me, you will be happy that you did!

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