Earlier articles have discussed insulin's role in our bodies, what happens when we don't have it, and why some of us have to take it by injection. But all insulins are not the same. How are they different? WHY are they different? And, how can we use their differences to better self-manage?
Insulins are described and subdivided by concentration strength, source, and time of onset/peak. This last category is most critical, but we really need an understanding of all three criteria.
Concentration Strength
All insulins sold in the United States today are of U-100 strength, 100 units
of insulin per cc of fluid. But there are other dilutions in other countries,
and if you were to encounter one of these (all perfectly usable), and inject
your usual volume of insulin, you'd get a different amount of insulin. You'd
get the wrong dosage.
Source
At one time, all insulin was produced by laboratory animals, most often cows and pigs. In the last decade, however, American insulin manufacturers have almost completely shifted to use of "recombinant DNA" (rDNA) technology, enabling laboratory production of a close analog to real human insulin. This "human" insulin is said to more closely match our endogenous (pancreatic) insulin.
Although labelled much like "animal source" insulins, recombinant DNA insulins are not quite the same, either in time of onset or in amount of insulin required. Experience shows that any switch between the one and the other must be done with care, and under your doctor's supervision-the types might be different enough to cause you trouble otherwise.
Time of Onset/Peak
The different insulin types: Humalog, Regular, NPH, Lente, Ultralente, Lantus, and the pre-mixes: 70/30, 50/50, and Humalog 75/25, are divided and distinguished by their time of onset and duration. As shown in the chart below, critical questions are:
1. When does this insulin begin to act in my body?
2. When does it reach its peak?
3. When does it fade to insignificance?
NOTE: We're all different! Charts reflect averages-you may well find a given insulin is different for you. Test frequently, keep good notes, and make your own chart!
The chart below is a general approximation, derived from data furnished by all three U.S. insulin manufacturers, Eli Lilly and Company, Aventis Pharmaceuticals, and Novo Nordisk Pharmaceuticals Inc.
INSULIN START PEAK END
Humalog/Novolog 10 min. 1 hr. 4 hr.
Regular 30 min. 2-5 hr. 8 hr.
NPH 1.5 hr. 4-12 hr. 22 hr.
Lente 2.5 hr. 6-16 hr. 24 hr.
Ultralente 4 hr. 8-18 hr. 30 hr.
Lantus
1.5
hr.
2-23 hr.
24
hr.
70/30
2
hr.
2-12 hr.
24 hr.
50/50 2 hr. 2-6 hr. 24 hr.
Humalog 75/25 15 min. 1-6.5 hr. 18/26 hr.
Where Humalog, Regular, and 50/50 premix have sharp and definable "peaks," the long-acting Lente insulins come on slowly, and have long, flat "peaks," and a slow rate of decline. New Lantus insulin (insulin glargine rDNA) is even flatter, and is meant, like the Lente insulins, to provide "basal" insulin coverage. Discuss your insulin choices with your doctor and your diabetes educator—they will help you find which is best for you.
There are a number of insulins not charted above. Some are "buffered insulins" (from both Lilly and Novo Nordisk), and there is a special U-400 insulin from Aventis. These are strictly for use in insulin pumps, and should not be used for any other purpose! There are also insulins not available in the United States (or not yet available), such as the complete line of Hypurin animal-source insulins manufactured by CP Pharmaceuticals of Great Britain, and other insulins encountered in other parts of the world.
Avoid Rigid Thinking
The most accurate chart will still be imprecise. Short-term, things will vary because diabetes, like life itself, is like riding a surfboard-no one can control all factors! Novo Nordisk says it best, on their chart: "The time course of action of any insulin may vary in different individuals, or at different times in the same individual. Because of this variation, time periods indicated here should be considered as general guidelines only."
Long-term, things will vary because your body is not the same from one decade, or one year, to the next. Your chart will need regular updating. Use it as guide, not gospel.
Mixes and Mixing
Although users of the insulin pump generally take only short-acting insulin, most insulin-using diabetics employ a mix of faster and slower insulins, to provide best control. The idea is to let the fast insulins (Regular or Humalog) cover meals, and let the longer-acting types (NPH, Lente, Ultralente) cover the period between meals. There is quite an art to insulin mixing, as you must consider diet, exercise, injection frequency, total insulin volume, ratio of slow-to-fast insulins, general health (including other medications you might be taking!), and your own unique intangibles. NOBODY is exactly "average."
Some folks employ commercially-prepared "pre-mixes," like "70/30" (70% NPH to 30% R). While these pre-mixed insulins provide a convenience (precise and consistent mixing) they also come with a liability: What if, to achieve optimal control, your best mix, right now, is 68/32, or 75/25? And what if tomorrow, due to variations in your diet, activity level, and general health, it's 60/40 or 81/19? You can't make fine adjustments with a pre-mixed insulin-you're stuck with the mix the doctor gave you-and for some, that means less than optimal control. Yes, you can vary your total dosage, total volume, and injection frequency; but, as the different insulins are really there for different purposes, adjusting insulin with a pre-mix can be like scratching an itch-with a sledgehammer. There can be consequences. You can get better control of your diabetes by mixing your own insulins.
A Caution
The insulin manufacturers report that certain insulin types should not be mixed; these could have dangerous consequences. The Lente insulins, long-acting insulins, should never be combined with intermediate-speed NPH insulin. Chemicals in the NPH would alter the Lente or Ultralente, turning it into an approximation of fast-acting Regular insulin! Mix those two, and you'll have a very different result than you might expect! Also, notes supplied with new Lantus insulin state: "Lantus must not be diluted or mixed with any other insulin or solution, as it may result in a delayed onset of action."
Be sure to talk to your doctor about appropriate and inappropriate insulin combinations.
Adjusting Insulin
People's bodies, and their insulin needs, change. Not only by the year, the month, or the decade, but, to achieve the best possible control, you may choose to vary your dosages by day, linking them to results of your blood glucose monitoring. To preserve optimal control, you will need to adjust your insulins, to compute, draw up, and inject different amounts and mixture percentages. Some folks, working with the full potential of "tight control," use a sliding scale, adjusting their insulins every day, in close step with their diet, exercise, and blood glucose test results. The rewards of their discipline-greatly reduced chance of complications—can be great.
Once you realize the role played by the different types of insulin, and how you can optimize your control by utilizing the most appropriate blend, right here, right now, you're well on the road to staying healthy. Knowledge is power!
Blind diabetics, and those losing vision, need to adjust insulin as well, and the technology to do so is available: Tactile insulin measuring devices like the Count-A-Dose enable reliable non-visual insulin measurement and mixing. Lack of sight is no bar to good control!
The Count-A-Dose (Two models, 1cc and ½cc "Low-Dose" model,
using B-D syringes) from Medicool (of Torrance, CA), is available from the National
Federation of the Blind, Materials Center, 1800 Johnson Street, Baltimore, MD
21230; telephone: (410) 659-9314. Cost is $40, either size. The Materials Center
is open 8:00 am to 5:00 pm EST, weekdays.