For many years, insulin products have been available with different durations of activity, ranging from insulin products that are rapid acting, able to lower blood glucose for only a few hours (such as regular insulin), to other insulin products with intermediate duration of activity (such as NPH insulin), to those with very prolonged activity, with effects on blood glucose lasting over a day (such as Lantus insulin). Combinations of these different insulins were found to lead to better control in maintaining a patient on only one type of insulin. One of the original combinations was to instruct the patient to use both rapid acting and intermediate acting insulin before breakfast and again before supper: the combination of NPH and regular before breakfast and NPH and regular before supper was widely used in the 1970's. Many other combinations have since been developed, but it has remained common for patients to be advised to inject two different insulin products at the same time of day.
Recognizing the possibility of selling a more convenient product for patients injecting two types of insulin, manufacturers developed combination insulin products, mixing a rapid-acting insulin together with a long-acting insulin in the same vial or insulin pen, and selling the combination as what is frequently called a "pre-mix." Premixed insulin products contain a specified percentage of each of the two insulin products. For example, one common premix contains 70% NPH and 30% regular insulin, and is known as "70/30" in the United States. Interestingly, in Europe, the same insulin is known as "30/70" - it contains the same percentage of 30% regular and 70% NPH, but the numbers are reversed in describing the product.
What insulin premixes are available
In the US, only 70/30, 75/25 and 50/50 ratios have been sold, although in Europe everything from 10/90 to 50/50 has been available (10/90, 20/80, 30/70, 40/60, and 50/50). In the United States, currently available pre-mixed insulins include mixtures of NPH and regular insulin, and two more recently-developed products, containing either insulin lispro (75% insulin lispro protamine suspension and 25% insulin lispro, sold by Lilly as Humalog® Mix75/25) or insulin aspart (70% insulin aspart protamine suspension and 30% insulin aspart, sold by Novo Nordisk as NovoLog® Mix 70/30).
Why use a pre-mix?
The theory behind using a premix is to decrease the hassle factor for patients - assuming they are on an insulin program that would contain the same insulins, in about the same ratio as what's in the premixed product, then the patient need not draw up two different insulins from two different vials into their syringe, but only tap the premix bottle once to get both insulins. The problem of course is that not everyone is on the precise ratio of longer-acting insulin and shorter-acting insulin that is sold by the insulin companies. This has led to loud arguments about the wisdom of convenience vs. control, which has eventually been answered, as the manufacturers have designed studies showing that premixed insulins do lower A1C as effectively as other insulins and better than pills, and as physicians have moved away from two shots a day (each containing two types of insulin) to more complex programs, such as basal/bolus insulin programs using 3 shots of mealtime rapid-acting insulin and once-daily basal insulin. Many physicians remain leery of using premixed insulins, as raising the premix dose to combat hyperglycemia at one time of day will inevitably lead to effects on glycemia at another time of day, when the other component of the premix is working, with the possibility of creating hypoglycemia as a consequence.
Today, many type 2 diabetes patients who are failing to control their hyperglycemia on oral agents are started on a single daily injection of basal insulin (such as bedtime NPH or Lantus or Levemir), whereas others begin with an insulin premix injected before the largest meal of the day. The choice is up to the physician, their knowledge of diabetes, and their estimate of what might best benefit the patient. In most patients, the oral agents are continued at the time of initiation of insulin therapy. Over time, the insulin program that was originally started will inevitably be adjusted, so that meal-time rapid acting insulin may be added to once-daily basal insulin, or a single shot of premix may be increased to using premix before two meals (usually breakfast and supper).
Some concluding thoughts about premix insulins
* Premixed insulin products contain two kinds of insulin. The first kind helps the body control blood glucose all through the day. The second kind helps the body control blood glucose at meal times.
* There are different types of premixed insulin.
* The different types of premixed insulin work equally well to lower A1C.
* The chance of blood sugar dropping too low is the same with the different types of premixed insulin.
* Some physicians routinely use premix insulins; others avoid them in favor of other insulin programs.
Also see:
Premixed Insulin for Type 2 Diabetes: A Guide for Adults
http://www.effectivehealthcare.ahrq.gov/healthInfo.cfm?infotype=sg&DocID=125&ProcessID=18
From the Agency for Healthcare Research and Quality
Premixed Insulin Analogues: A Comparison With Other Treatments for Type 2 Diabetes.
http://ana.effective-healthcare.info/insulin.html
From the Agency for Healthcare Research and Quality
Type 2 diabetes: the role of insulin
http://findarticles.com/p/articles/mi_m0689/is_5_54/ai_n13784743/pg_5
From the Journal of Family Practice
Product information for Humalog® Mix75/25
http://pi.lilly.com/us/humalog7525-pi.pdf
From Eli Lilly
Information about NovoLog® Mix 70/30
http://www.novomedlink.com/products/NovoLogMix/novologmix-home.aspx
From Novo Nordisk
