April 23, 2002
Insulin
Question from Racine, Wisconsin, USA:
For 20 years, I have been taking the Regular and NPH individually and in combination depending on when they are taken. I take three injections a day (before breakfast and supper and at bedtime), and my hemoglobin A1cs are normally in the 5.5-6.5% range. I have had pretty good success with these two insulins but also had some problems with low blood sugar mainly after going to bed, and I think I can resolve the late lows and help the daytime control by using the Humalog. I am trying to get equations for the responses of the different types of insulin I take to be able to approximate the peak time and relative magnitude at the peaks. I have tried to get these equations from my regular doctor, and an endocrinologist he referred me to, but was unsuccessful. The specialist I saw was not at all interested in giving me the information I was looking for. I do not believe he had it himself and did not seem to like the idea of a lowly patient trying to get it. I also tried to get this information from the insulin manufacturer but only got through to a PR person who told me I had to see my doctor because there were to many variables to give out what i’m looking for.
Anyway, I believe if I had the equations I could plug in different values and add them to get some valuable information to use as starting points. I know I am not a doctor, but after taking three insulin injections a day and thousands of blood tests over the years, I have learned quite a bit about the problems involved. I had already checked the Lilly web site and have the time activity profiles. What I need are the actual equations for these profiles so I can work with them. What would be even better would be software that could do the math.
Answer:
I am afraid you will be frustrated by the answer I have for you. First, there is a high degree of intra-individual, as well as inter-individual, variability in blood sugars. Thus, this reflects the variability in the insulin levels achieved. Most textbooks provide a range of time for the action curves of insulin. In order to find the half-life of insulin for you, you would have to inject labelled insulin and take multiple blood samples, working a multiple compartment model.
This is too complicated to apply to clinical medicine, especially with all the variability. Where does all the variability in insulin levels come from? It comes from use of a variety of injection sites, level of activity (reflecting regional muscle blood flow), physical integrity of the insulin, presence of intercurrent illness, just to name a few. You might be better off using the ranges of activity to make day-to-day changes or adjustments.
JTL
[Editor’s comment: You might check out Stop the Rollercoaster by John Walsh. I believe it might have some ideas along the lines of what you are looking for.
SS]
