A good way to improve your glucose levels is to track the peaks and drops in your glucose, so you can figure out why they happened and how to correct them. Once you identify glucose patterns (they ARE there!), you also want to understand when each of your insulins is active and when they typically stop lowering your glucose. This helps you adjust your doses or food intake to stop unwanted ups and downs in your readings.
The table below shows the start, peak, and end times for various insulins with some explanations and typical uses for each.
|Action Times for Insulins|
|Insulin||Starts||Peaks||Ends||Low most likely at:||Usage|
|Hum/Nov/Apidra||10–20 m||1.5–2.5 h||4.5–6 h||2–5 h||designed to peak, covers meals and lowers high BGs|
|Regular||30–45 m||2–3.5 h||5–7 h||3–7 h|
|NPH||1–3 h||4–9 h||14–20 h||4–16 h||intermediate, less peaking, larger action|
|Lantus||1–2 h||6 hr||18–26 h||5–10 h||designed for flatter and longest action, background insulin action for keeping your BG flat when fasting|
|Levemir||1–3 h||8–10||18–26 h||8–16 h|
Humalog, Novolog, and Apidra insulins currently give the best coverage for meals and help keep the glucose lower afterward. Their glucose-lowering activity starts to work about 20 minutes after they are taken, with a gradual rise in activity over the next 1.75 to 2.25 hours. Their activity gradually falls over the next 3 hours with about 5 to 6 hours of activity being common with these insulins. Although “insulin action times” are often quoted as 3-5 hours, the actual duration of insulin action is typically 5 hours or more. See our article Duration of Insulin Action for more information on this important topic.
In general, “rapid” insulins are still too slow for many common meals where the glucose peaks within an hour and digestion is completed within 2-3 hours. The best-kept secret on stopping post-meal spiking is to take the injection or bolus earlier before the meal and to eat slower low glycemic carbs.
Regular insulin still carries its original name of “fast insulin” but its slower action often works better for people who take Symlin or for those who have gastroparesis (delayed digestion). It is also a great choice for those who may not have insurance coverage or have an excessively high co-pay for insulin.
Though often thought of as being 24-hour insulins, Lantus and Levemir are actually 18 to 26-hour insulins. At least a third of all users do not get a full 24 hours of action from these insulins. Those who experience shorter activity times may also notice more peaking in activity and a tendency to have lower readings about 6 hours after the injection. A larger peak in activity at around 6 hours is usually associated with a shorter action time, and vice versa. Anyone who does not take their long-acting insulin at about the same time each day can also experience gaps and stacking of insulin with a single injection a day. Smaller doses are also often associated with greater insulin activity at 6 hours with less at 18 hours and beyond. More peaking usually indicates less than 24 hours of activity.
If your Lantus or Levemir “wears out” before the day is done, this can cause unexplained highs before or soon after the time when the next dose is given. It can also cause low readings during its peak activity. For instance, if Lantus is given only at bedtime, night lows may become more likely due to a peak in activity, while if one injection is given in the morning, high readings may occur before breakfast due to the lessening activity from the previous dose.
Splitting doses of “24-hour” insulins into two equal doses with half taken in the morning and the other half taken in the evening even out dosing gaps and minimizes peaking. After splitting a single dose of Lantus or Levemir, many people find they have better readings.
NPH has a shorter action and more peaking than Lantus or Levemir. This can be useful at times. For example, if a teen or young adult has a Dawn Phenomenon or someone with Type 2 diabetes sees their glucose rise in the early morning hours due to release of more free fatty acids during sleep, NPH can be taken at bedtime to provide the extra insulin needed during the late morning hours. Bedtime NPH can be combined with an injection of Lantus or Levemir at breakfast to cover the daytime hours. A bedtime dose of NPH can also be combined with two daytime injections of NPH before breakfast and lunch to reduce the number of injections required in a day. For those who use a syringe, NPH can also be combined with the rapid insulin taken for a meal into a single injection. Like Regular insulin, NPH is also much less expensive. If the cost of insulin is a concern, try splitting the current dose of Lantus or Levemir into 3 equal injections of NPH each day. Most people find this provides very stable basal insulin action once the total dose is dialed in, along with any increase in the bedtime dose that may be needed to offset a Dawn Phenomenon or Type 2 diabetes.