INSULIN TYPES: A REVIEW
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 an understanding of all three criteria is needed.
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.
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" 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, and the pre-mixes: 70/30 and 50/50, 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!
Below is a general approximation, derived from data furnished by both U.S. insulin manufacturers, Eli Lilly and Company and Novo Nordisk Pharmaceuticals Inc.
INSULIN START PEAK END ------- ------ ----- -----
Humalog 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
70/30 30 min 2-12 hr 24 hr
50/50 30 min 2-6 hr 24 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. They are hard to describe in specific terms.
There are several insulins not charted above, "buffered insulins" from Lilly and Novo Nordisk, and a special U-400 insulin from Hoechst of Germany. These are strictly for use in insulin pumps, and should not be used for any other purpose!
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: "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 fast- 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), or "50/50." 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 premix can be like scratching an itch--with a sledgehammer. There can be consequences.
Both U.S. insulin manufacturers report that one insulin mix could have dangerous consequences, and should be avoided. The Lente insulins, the longest-acting insulins available, 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! Be sure to talk to your doctor about appropriate and inappropriate insulin combinations.
People's bodies, and 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 can be greatly reduced chance of complications.
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, 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 Jordan Count-A-Dose enable reliable non-visual insulin measurement and mixing. Lack of sight is no bar to good control!
The Count-A-Dose (Low-Dose model, B-D 50-Unit syringe) is available for $49.95 from Jordan Medical Enterprises, 202 Oaklawn Ave., South Pasadena, CA 91030; telephone: 1-800-541-1193. An instructional audiocassette is available. Both the Low-Dose model and the now-discontinued 1cc, 100-Unit Count-A-Dose are also available ($40, either model, but no cassette for the 1cc model) from the National Federation of the Blind, Materials Center, 1800 Johnson Street, Baltimore, MD 21230; telephone: (410) 659-9314. The Materials Center is open 12:30 to 5 pm EST, weekdays.