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June 18, 2003

Insulin Pumps

Question from Utah, USA:

My 10 year old son started on a pump about a year ago, and at times his basal rates are very low (0.3-0.5 units per hour). We have noticed what appears to be great variability in the delivery of these rates, and our son's physician suggested the small amounts may be being delivered erratically, even though the pump specifications suggest they are within appropriate parameters. He suggested that we dilute the NovoLog so that more volume of fluid was delivered with each dose which would possibly decrease the variability of delivery. However, the NovoLog package inserts states that diluted Novolog should never be used in a pump. Further, I cannot find literature describing the use of NovoLog in this fashion. My concern is not that this is an off label use, only that I don't know what the possible outcomes of diluting insulin in a pump might be. I have several questions: Will this mixture remain stable for to four three days while in the pump reservoir? Can it separate leading to hyper- or hypoglycemia? Should we change the insulin on a different schedule when diluted? Should we periodically try to "mix" the insulin while in the reservoir? Can we dilute batches of NovoLog and draw from it over time? If so, how long can we store it? Refrigerate? If you could share your experiences or any literature citations on this subject I would appreciate it. As Humalog has been available longer, perhaps you have experience/literature citations with it that might be applicable.

Answer:

Humalog diluent is available from the manufacturer, and your son’s diabetes team can arrange to get this for you. To my knowledge, NovoLog diluent has not been made available by the manufacturer, although many of us have requested it.

Your question about stability of insulin in insulin pumps is a good one, but there is not very much specific information, only anecdotal information. We routinely use Humalog with diluent and do not have stability problems. Your son’s diabetes team is also correct that some of your problems could be intermittent administration with such low flow rates in the tubing and diluting and thus using larger volumes may solve some of these problems. It is certainly worth trying.

SB