Does Lilly diluent work with Humulin N?

I recently received diluent for insulin from Lilly, thanks to information on this forum.
I use Humulin N, and the label on the diluent says it’s for use with Humulin R (and other insulin types, but it doesn’t say Humulin N).
Does anyone know whether the diluent would be safe to use with Humulin N?


Of course you mileage could vary, and @Eric may have already tried it, but I feel like diluent is diluent. Anything like a preservative etc, would be in the insulin which you will be diluting. So I wouldn’t expect diluted insulin to last as long as the non-diluted variety. But I would use it without issue.

edit - Welcome to FUD! Great question.


Hi @Nora,
I have never diluted NPH. I can’t really say for sure.

But it might be useful to examine what you are trying to do.

NPH has a fairly long span, like 12 hours or so.

If you use a 1/2 unit pen or syringe, that means you have increments of 1/2 a unit over 12 hours. That’s like .04 units per hour, which is a smaller increment than most insulin pumps give you.

Is this for a little one? Do you have 1/2 unit dosing already?

If you are trying to increment NPH in a smaller dose per hour than 0.04 units, there might be a problem that can be fixed in another way.


If Lilly did not specify that it could be used with NPH DO NOT USE IT. Insulin formulations have different buffers to maintain the shape (structure) of the molecule to maintain it’s effectiveness. For example, the amount of zinc in the buffer for the various insulin differs Call Lilly and ask.

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Hi @Eric,

It’s a very little one. I’m a pet parent, with a beloved toy poodle who recently developed type 1diabetes. (Same illness for people and dogs. I’m learning about this as we go along.) Treatment protocol for dogs is 2 insulin injections daily 12 hours apart.
There’s no vetsulin in Israel where we live. Apparently the market is too small. So dogs are prescribed Humulin N. Half a unit is too much for him and he’s had numerous hypoglicemic events. Giving precise amounts with a syringe at less than half a unit is almost impossible. He became blind in a matter of weeks, and underdosing could cause cataracts to hypermature which is painful for dogs.
So I’m really hoping the diluent works with Humulin N.
Any other suggestions would be very very welcome.
And thank you Eric for the info you posted about the diluent and sterile vials.


Thanks Mike. I called them. They said they don’t have diluent for Humulin N and they don’t recommend diluting it.
If it works even for a week it’s still a good option, but I don’t know how to check.
Wondering whether anyone has tried it before.


Hi @Nora
I am sorry about your dog needing to deal with diabetes. It’s tough because they can’t describe their symptoms to you.

I think diluent would work in this situation. The only thing diluent does is take up volume in the syringe.

Humulin N is durable. I have used it a lot in previous years before using a pump. It certainly won’t amplify the insulin. I think it’s a safe thing to do.

I hope you will try it out and let us know.

Do you have diluent and vials and 1/2 unit syringes?


I do have diluent, vials and 1/2 unit syringes.
Thank you for asking @Eric.
Wondering whether the diluent would somehow break down the insulin molecule and ruin it.
If I don’t find a better option I’ll test it.
Another thought -Do you know of any smaller syringes? Ones that would be precise at less than 1/2 a unit?


Another kind of crazy thought, but here in the US you can relatively easily obtain an older insulin pump that is long out of warranty and people don’t want anymore. If you could get your hands on one of those, you could leave a set in the pooch, and just connect and dose then disconnect until the next dose is needed, and a pump can deliver tiny doses of insulin.


That’s interesting @Chris.
The option hadn’t even occurred to me.
Can a pump deliver a dose that is smaller than half a unit?

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It depends on the pump, but most of them can go down to 0.05 units.

The other thing about what Chris mentioned, you would not need to actually attach the infusion set. You could insert it, inject, and then remove it. Basically use it like a syringe instead of an infusion set.

A different option would be using Lantus. That gives a longer coverage, so a 1/2 unit of Lantus would not be as strong as NPH because it would be spread out over a longer time.

I do think diluting NPH would work. I can test it out if you want me to.


OMG Eric, if you would be willing to test diluting NPH that would be incredible help.
Yes please!


I’m so glad I posted. You’re giving me such great ideas and support.
I’ll look into both the Lantus option and the pump.
We’ve had Freestyle Libre attached to the pooch several times and since he’s so small attaching it seems to be quite painful for him .
How often do you need to replace the canola for the pump?
And how painful is it for you?

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If you are only using the pump to delivering a small amount of insulin, and not keeping it attached, there is no reason to actually attach the canula. Use it as a syringe.

Use a steel infusion set. Insert it, hold it still (and hold the dog still :grinning:) while you deliver the insulin, and then remove it.

I think Lantus is your better option though. Do you need some?

Also, diluting NPH definitely works. I tested it out. I don’t know how long it will last once it has been diluted, so it might be best to do it in small batches so it doesn’t sit too long.

You can actually dilute it in the syringe. Draw 5 units of diluent into the syringe, and then draw 5 units of NPH, and roll the syringe vigorously in your hands to make sure it is completely mixed. Then expel everything out of the syringe that you don’t want to inject into your dog before you insert the syringe into him.

So if you mixed 5 units of diluent and 5 units of NPH, and you want to only inject him with 1/4 unit of NPH, you would expel all but 1/2 a unit of what is in the syringe. Since you mixed an equal amount of NPH and diluent, the syringe is now 1/2 strength, so 1/2 unit in the syringe is now only 1/4 unit of actual NPH.

Does all that make sense?

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I think Nora mentioned they are in Israel. I am guessing they can purchase it over the counter for a very reasonable amount.


I’m not sure what the rules are for getting insulin there.

The animal basal generally used in the U.S. was vetsulin, which is a form of NPH and made from pigs. They did not normally use Lantus, probably because of the cost. But studies showed Lantus was effective for dogs and cats.

I am not sure if she would need a script for Lantus over there, or what it costs. From what she said, I am not sure if a vet would cooperate with that effort.

But if she can’t get it over there, she can have it for free if she wants.

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Gotta say it again…

Diluted NPH definitely works!!!

Excuse me while I get some more chocolate.


Thank you for testing the diluent with NPH!
Very happy to hear it works!
Regarding diluting in the syringe, I tried a few times with sterile water and it didn’t work at all. The insulin and the water didn’t seem to mix well, and I didn’t want to mix too vigorously as I was worried I’d be ruining the insulin.
I’ll try it with the diluent now that I know it works. Maybe it mixes better. How vigorously do you roll it? And do you also add air into the syringe to help it mix?
If you find out how long a diluted batch works please do let me know. If it’s more than a couple of days I’ll dilute in a vial.
Thank you for the offer to send Lantus. You’re too kind. If I try switching to it I’ll try to get it in Israel first. If that doesn’t work I’ll get back to you.
Did you mean that Lantus is preferable to NPH because it would have a weaker effect that lasts for a longer time? Would that also mean no need to dilute?
I’m going to try diluting the NPH and see how that goes.
The diluting math makes complete sense, thanks.


Sort of, the Lantus releases the insulin you inject over 21-23 hours, so the amount you inject would be spread out over more hours, instead of the twice daily NPH which peaks at approximately 5 hours. The action curve of the Lantus is much flatter as well, so no big peaks in insulin action twice a day.


Physical force will not break a molecule and the physical force you can apply by hand will not de-nature a protein (which is what insulin is); you need an optical tweezer to do that. I suspect the single most extreme force you have subjected insulin to is injecting it.

Personally I shake, rattle and roll insulin vials all the time. I also whack them with my finger along with the syringe to remove the bubble and I curse at them quite frequently. Of these activities the last is the only one likely to damage the insulin, and only if I make the mistake of believing in the God I am cursing.

I suspect the “rolling” thing comes from people who haven’t tried it or, maybe, people who think you or I might let go and loose the Insulin against a wall, thereby denaturing the vial but not the insulin.