April 11, 2001
Question from Kansas, USA:
I’m confused. I just read a comment about mixing Humalog and NPH. It said, “you probably can keep the Humalog and NPH together for about 1 hour”. Does this mean I shouldn’t mix an evening dose in the morning to use later? We’ve done this before for our son, and seems to work fine if we roll it before it’s injected. Does the insulin not work the same if it’s mixed?
Lilly specifically advises that NPH and Humalog mixed will change the profile of the insulin because the Humalog and the Regular in NPH will change places to some extent on the protamine, with some Humalog binding and some Regular being unbound.
[Editor’s comment: Indeed, mixing two insulin products together into one syringe has a potential for interaction of the products, with alteration of the time course of how they act. This was a major problem many years ago, with a now-unused long-lasting insulin product called “PZI” when mixed with Regular: the combination lost all of the Regular effect as far as when the insulin combination worked, and it acted as if it were only a bigger dose of PZI. This is usually a minor problem with other insulin mixtures, but it is advised to not mix and then store the mixture (or in rare circumstances when mixing ahead of time is the only way to handle a situation, such as a visiting nurse filling syringes in advance for an elderly housebound patient, that it be done consistently rather than occasionally).
It will also be important not to mix Lantus (insulin glargine) with other products when it becomes available.