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One night early this year, I received a call from a nurse at a nursing home. A resident accidentally had been administered 32 units of insulin aspart (NovoLog, Novo Nordisk), a rapid-acting insulin analog, instead of the ordered insulin glargine (Lantus, Sanofi-Aventis), a basal or long-acting insulin. The nurse's call averted what was a potentially fatal medical error. Is this an isolated event?
Although to my knowledge no data are available to show this, these types of phone calls have probably become more common over the past 5 years, especially if we consider that the same type of mistake could be made by patients in their homes and by nurses in hospitals. The cause of this particular medical error seems obvious to me—similar packaging for different medications—but probably is more complicated.
CLOUDY AND CLEAR
The history of cloudy long-acting insulins goes back 70 years, when protamine and zinc initially were added to regular insulin to prolong its activity.
The introduction first of protamine zinc insulin (PZI), followed by NPH and the lente series of insulins, was thought to be a tremendous benefit to patients with diabetes. Before PZI, regular insulin was required four times daily for those with severe insulin deficiency. Many thought that PZI, NPH, ultralente, and lente insulins could be provided once daily.
History would prove that this added convenience did not necessarily improve long-term outcomes. The Diabetes Control and Complications Trial (DCCT), published in 1993, definitively showed that regimens of once- or twice-daily insulin resulted in worse microvascular and neuropathic outcomes than did multiple-injection regimens using mealtime regular insulin as part of an entire program of intensive therapy for type 1 diabetes.1
Nevertheless, it was quite simple to recall that the cloudy insulin was always the long-acting insulin, while the clear insulin was short-acting. This did not change for decades, although the emphasis on providing short-acting prandial insulin grew after the publication of the DCCT findings. Even when the first insulin analog, insulin lispro (Humalog, Lilly), was introduced in 1996, we still could differentiate the longer-acting insulin preparations (cloudy) from the short-acting and now the "rapid-acting" insulin analogs (clear).
Then, in 2001, insulin glargine, the first long-acting basal insulin analog, made its debut in the U.S. This one looked different from previous basal insulins. Glargine was the first long-acting insulin that was clear instead of cloudy.
No one was more excited about this added tool than I was, and I continue to be enthusiastic about both basal insulin analog products (the second, insulin detemir [Levemir, Novo Nordisk], was released this spring). Glargine forced both patients and clinicians to think about insulin in a more physiological manner, separating the basal from the prandial components of insulin therapy.2
CAUSE FOR CONFUSION
It wasn't long before we started receiving phone calls like the one noted above. It is quite easy to see how such an insulin mix-up could occur.
In my teaching clinics, it is rare for an internal medicine resident even to know how much 1 unit of insulin is. Indeed, I would also submit that most providers who prescribe insulin are not familiar with the differences in appearance of various insulin vials and labels.
To test this hypothesis, I asked 13 general internists, all with large numbers of patients with type 2 diabetes, to identify three types of insulin. The papers on these vials were removed, although there are subtle differences in the vial shape and in the color of the vial top. This very nonscientific survey revealed that only 3 of the 13 internists knew each insulin type, while 5 were aware that glargine comes in a tall, skinny vial.
PENNING A PROBLEM
Until recently, insulin pens were not frequently used in the U.S., particularly compared with Europe. Depending on the type of pen, the insulin might not always be visible, thus causing concern about a mix-up. As for medical errors with insulin injected with a traditional syringe, problems differentiating the cloudy from the clear have been relatively uncommon, since the insulin itself is always visible.
Up until now, I have suggested that patients take one insulin with a pen and the other with a vial and syringe. Because many people find insulin pens more convenient, they take their prandial insulin with a pen and their basal insulin from a vial. But many patients (including hospitalized or nursing-home patients) do not have access to insulin pens.
Adding to the potential for problems is the fact that even the insulin analogs (detemir and aspart, glargine and glulisine [Apidra, Sanofi-Aventis]) are administered in similar pen devices! Glargine and glulisine cartridges fit in the exact same pen, and the detemir pen and aspart pen are almost identical except for a small stripe. Will this result in even more mistakes? The risk of a life-threatening error is very high.
Of even greater concern is the forthcoming availability of glulisine in a vial with a shape similar to that of the glargine vial. There will be subtle differences in the color of the top, but will this have an impact on insulin errors in patients' homes? Will hospitals that use glargine and glulisine as their two analogs be more prone to errors than if they were using glargine with lispro, which has a maroon top that easily sets it apart from glargine?
I don't want to wait for the data to come in. I can see the errors waiting to happen. I don't blame the insulin manufacturers for causing this problem. I am told they have tried diligently to get the Food and Drug Administration (FDA) to do a better job of standardizing insulin packaging.
I would like to see uniformity in packaging for similar types of insulin, such that all long-acting analogs would come in one vial shape and all rapid-acting analogs would come in another obviously different vial shape, regardless of which company manufacturers them. I would like to see different bright colors used on the packaging of each type of insulin. This also should be insulin-specific rather than company-specific. I would suggest that the rapid-acting insulins lispro, aspart, and glulisine could be packaged in traditional insulin vials all marked with one color that would be difficult to miss, whereas long-acting glargine and detemir would both come in long, skinny vials bearing a different distinctive color. But I would leave those details to the FDA and the insulin manufacturers.
What I do know is that the packaging being used now is not working to help
prevent medication errors, and I am afraid the situation will get much worse
before it gets better. 
Footnotes
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References
2. Hirsch IB: Insulin analogues. N Engl J Med 352: 174–183, 2005.
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