BEFORE YOU START: Please note that although I currently volunteer for both the Stroke Association and Age UK, the views expressed in this blog are strictly my own. I am not a spokesperson for either (or, indeed, for any) organisation, and I accept complete responsibility for the views expressed herein. I've tried to use the Glossary to explain any ambiguous terms, but if you think there is anything I've missed, please message me.

Saturday, 13 January 2018


I've been meaning to talk about this for a while, and am just about getting around to it.

The drug I take to regulate my diabetes is insulin, I will attempt to describe the process below. A lot of the information here I take from the electronic Medicines Compendium (eMC) web site, which is one of the resources used by clinicians in the UK. Quickly on this note, the eMC seems squarely aimed at a UK audience, and these drugs might have different names or compositions in different countries, so if you live outside the UK please bear this in mind.

My insulin is ultimately injected into my tummy, and for this reason comes in a syringe which is called a "pen", shown below:

To the left-hand end of this, I screw in a single-use (sterile) needle so as to inject myself (the pen is used multiple times).

What's in the pen?

The pen contains a product called Humalog Mix25, by drug firm Eli Lilly. I think this is just about the only prescription I've ever had which specifies both manufacturer and product names. Mostly, meds are named generically. The pen comprises two active ingredients,

  • 25% insulin lispro solution, which is a fast-acting insulin (around 15 mins), and
  • 75% insulin lispro protamine suspension (intermediate-acting, I can't see a definition of what they mean by this, although they do have a chart on their entry in the eMC)

The list of "non-active" ingredients (the solvent) is detailed on the eMC web site, although I shan't discuss it here.

To see what the difference is between a solution and a suspension, there's a video on Youtube. I can't find data on how concentrated these solutions/suspensions are compared to the solvent, although it appears to be somewhat arbitrary. It is certainly consistent for pens of a certain brand (so if you set a pen to dispense a certain dose, you get the same dose as you did with the last pen etc.), but not for pens of different brands. So, if I were to change the brand of insulin that I use, I would need to work out my dose from scratch once again.

How do I measure my dose?

Talking of dose, you can hopefully see, toward the right end of the pen, a dial. I can wind this dial both ways between 0-60. As you wind, the plunger moves in and out, just like a screw, varying the dose of insulin you'll receive. The gradations are called "units". The term "unit" is ubiquitous, although again the number of units of one type of insulin does not necessarily correspond to that same number of units of another type of insulin. Not all insulins are equal! I won't go into the different types of insulins available right now, but certainly there are faster- and slower-acting varieties, and I would assume that different manufacturers use different concentrations (insulin vs. solvent). Then there are mixtures of different types of insulin, like my pens, which are entirely proprietary.


One of my pens contains 300 units, in theory. In practise I think this varies slightly from pen to pen. Anyway, this corresponds to 3ml of the (insulin + solvent) mixture. So if you take a dose of, say, 50 units, you're talking about fractions of a millilitre. For me, each pen lasts roughly half a week (on two injections per day). Doses tend to go up over time (but slowly), presumably because one's pancreas gradually does less.

In terms of storage, I need to store unused pens in the refrigerator, although in theory they can be stored there for up to 3 years. Once I've started using it, I don't (i.e. I'm instructed not to) keep it in the fridge (in fact it's good to store under 30°C), but I have to use the pen within 28 days.

At the highest level, these pens come in boxes of five. And I submit a prescription for one box at a time (so five pens, around 2½ weeks of meds).


One last thing, I'm not a clinicial so please don't use what I've written as the basis for any treatment of either yourself or of others. If you do this, understand that it is at your own risk. I'd certainly advocate you getting to know your own meds, and taking control yourself, but the purpose of this article is simply to illustrate what "taking insulin" is all about for me. If you notice any errors, please either contact me or post a comment, and I will correct the article as soon as I am able.

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