(June 13, 2010)
The Role of PreMixed Insulins
Insulin comes in many formulations, sometimes in pens and sometimes in vials. They may be short-acting, rapid-acting, long-lasting, or intermediate in duration of action. An interesting variation is called "premixed insulin" or "mixture" insulins, because two different insulins of two different durations are premixed at the factory into one solution. They can provide some degree of blood sugar control at meals, between meals, and even at night, depending on your treatment plan and how much insulin that your pancreas is still making.
Premixed insulins contain a percentage of a rapid-acting insulin or short-acting insulin such as Humalog (insulin lispro) or Novolog (insulin aspart) mixed with a longer-acting ("basal") insulin. Current brand names in the US include Humalog Mix75/25 and Humalog Mix50/50 from Lilly and NovoLog Mix 70/30 from Novo-Nordisk.
In the United States, the names of the products indicate what percentage of the product is longer-lasting, followed by the what percentage is shorter-acting; that is, a product with 70/30 as part of its name has 70% longer-acting, and 30% shorter-acting insulin. But in Europe, other conventions are used: for example, in the UK, the product named Humalog Mix25 consists of 25% insulin lispro solution and 75% insulin lispro protamine suspension, Humalog Mix50 consists of 50% insulin lispro solution and 50% insulin lispro protamine suspension; and NovoMix 30 contains soluble insulin aspart and protamine-crystallised insulin aspart in the ratio of 30/70. (Why crossing the pond would result in reversing the nomenclature is something I'll leave for others to speculate about!)
When should premixed insulins be considered for use? In type 2 patients who are making some insulin, but where pills are insufficient, and insulin therapy is being considered, the choices for the diabetes team include adding long-acting (basal) insulin such as Lantus or Levemir to the pills the patient is already on, switching to a multiple-shot program (called MDI, multiple daily injections) or adding one or perhaps two shots of a premix given at mealtimes. The long-acting insulin will usually provide excellent overnight coverage to combat the dawn phenomenon as well as providing a basal amount of insulin around-the-clock with a once-daily dose; the MDI program can provide excellent around the clock coverage as well as excellent blood glucose control after eating but with the penalty of multiple injections and complexity of dosing instructions; the premixes can provide simplicity as well as moderately successful coverage.
As I've discussed previously elsewhere, 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. Most endocrinologists vote for control, and don't often recommend premixes. However, for patients who need supplemental insulin, and are just getting started with insulin injection therapy, they may be an acceptable alternative.
[Editor's Note: Also, see Premixed Insulin Analogues: A Comparison With Other Treatments for Type 2 Diabetes]