Happy Saturday, all! Welcome back to**Ask D’Mine**, our weekly advice column hosted by veteran type 1 and diabetes authorWilDuboisin New Mexico, who happens to have experience as a clinical diabetes specialist. This week, Wil takes a look at that pesky diabetes math that becomes even more confusion when applied to various insulin brands, pen sizes and dosing formats…

{*Got your own questions? Email us atAskDMine@diabetesmine.com*}

**Maureen, type 1 from New Jersey, writes:** *Well, my question seems pretty simple, but I just can’t figure it out. I take NPH at bedtime, only 12 units. It’s Humulin N in a U-100 KwikPen. The pen has 3ml. How many days should my pen last? It never lasts as long as I think it should. I must be doing something wrong…*

**Wil@Ask D’Mine answers:** Your pen should last exactly 14 days. Here, let me guide you through the math, which isn’t as simple as it seems, as insulin pen mathematics are laced with an ambush or two.

Now, logically starting at the logical start, a 3ml pen of U-100 insulin has 300 units, as there are 100 units per mL, which is where the whole “U-100” thing comes from (3 x 100 = 300). So if you take 12 units per day, the pen should seemingly last 25 days (300 ÷ 12 = 25), right? But the pen, as you’ve found, doesn’t last as long as the math indicates it should.

So WTF?

Is Eli Lilly short-changing you? Not quite topping up those pens to make an extra few bucks at our expense? I’ve got a friend who has four pill boxes, instead of the single weekly box most of us use, and she loads them up for the month all at once when she picks up her meds. She was shocked to discover recently that her pharmacy shorted her two pills on each of her prescriptions. It seemed so unbelievable she figured she made a mistake. But it happened again the next month.

Now, this seems like such a small larceny as to hardly be worth it, until you consider that Americans filled 4,468,929,929 prescriptions in 2016, the most recent year I could find reliable data for. If you multiply that by 30 pills in a typical month, you get a number so big I couldn’t even make sense of it, so I put it into one of those digit-to-words converters. The answer? One hundred thirty-four billion and change. Pills range in price from a penny or less to who-knows what, but you can see that millions could be made “shorting” us.

But that’s not what’s going on here. At least I don’t think that’s what’s going on. I confess, I’ve never drained a KwikPen and measured the volume. That might be a fun science project for my home-schooled kiddo. But possible larceny aside, there’s an ambush lurking inside your insulin pen, and you set yourself up for it either by paying attention to your doc, listening to your diabetes educator, or reading the patient instructions.

And those patient instructions for your pen, in Step 8, tell you to prime the pen before each injection, warning: “If you *do not *prime before each injection, you may get too much or too little insulin.” The bold typeface is theirs. You know, to make sure you’re paying attention. Now, how skipping the prime could possibly give you too much insulin is beyond me, although skipping the prime can defiantly short-change your dose. But priming before each injection, as you’re instructed to do, takes a bigger bite out of your insulin supply than you might suppose. The instructions say to start with priming two units. If you don’t see insulin at the tip of the needle, you are to repeat the prime.

Up to four times.

In all likelihood this process will eat at least three of the units in the pen’s reservoir each time you prime. That realistically ups the ante of your 12-unit dose to 15 units, and suddenly the pen you thought would last 25 days is dry on day 20. Priming once per day ate *five days* of insulin over the life of the pen.

Not that you shouldn’t prime. You do need to. And for most folks it doesn’t matter, because very few people have a dose that exactly matches the volume of a pen, and if they did, the doc could easily write the script for a slightly higher volume to compensate for the daily priming. Although this issue becomes much more important with rapid-acting insulins, where you could have 6-8 primes in a day, adding up to as much as 720 units of “wasted” insulin per month—more than two full pens’ worth squirted into the air!

But wait, you say. How on earth did you get to 14 days for my pen? Adjusting for the prime should still give me 20 days. What happened to my other six days?? I want my six days back!

Remember I mentioned an ambush or two? The priming was the first ambush. The second ambush is below Step 17 in the patient instructions, which tells you how to put the cap back on the pen. Actually, it’s a bit below that in the middle of page 8 of the instruction sheet, down below the section on disposing of pens and needles, in the section called “Storing your Pen.” It’s nearly the last thing in the instructions, right between “the used pen may be discarded in your household trash” and “keep your pen and needles out of the reach of children.” That’s where is says: *“Throw away the Humulin N Pen you are using after 14 days, even if it still has insulin left in it.”*

Yep, old-fashioned N insulin doesn’t even last as long as a quart of milk. So it doesn’t matter how much you use or don’t use, at the 14-day mark, it goes in your household trash. Assuming that your household trash is out of the reach of children, that is.

Isn’t that wasteful? Not necessarily. Your dose is on the light side, as is common with type 1s. A type 2 would easily use that pen up in a week, or maybe less. Heck, your pen is fully capable of delivering 60 units in one push. At doses that high, even without compensating for priming, the pen would be dry in five days. The real waste, of course, is putting something into your body that doesn’t work. The 14-day limit exists for a reason. The very nature of how N insulin is made gives it a short lifespan once the cartridge is pierced by the first needle, and nothing can change that.

Now, N, also called NPH is an old-school insulin that dates back all the way to 1946. By all rights it should be extinct, but it’s made a comeback. Why is that? It’s cheap, that’s why, and we are all poor. In some cases health plans don’t want to cover state of the art meds, in other cases PWDs simply can’t afford the copays on the “good stuff.” So NPH is *baaaaaaaack.*

Whether you are new to N, or you’ve not used it in decades, here are a couple of quick factoids to help you get the most out of this affordable, but short-lived, juice:

- Keep your stash of unopened pens in the fridge. Don’t let them get pushed to the back, because if they freeze they won’t work. The butter compartment was really designed by PWDs.

- Unless you live in Death Valley with no air conditioning, keep your active pen at room temperature (up to 86°F). Keeping it cold won’t extend its life, and cold insulin stings when you inject it.

- N needs to be mixed before each use. For pens, roll them between your hands ten times, then grab the pen by the base and flip it up and down ten times. Make sure you have a good grip on the pen so you don’t put your eye out. A little bead inside the pen helps mix the insulin. Well mixed N should be white and cloudy. If you have sections of clear and cloudy, keep mixing.

- N doesn’t have a “flat” action profile like modern basals. It has a significant peak action point, usually around 8 hours after injection, which has the potential to trigger a wicked hypo while you are sleeping. The old-fashioned workaround is a high fat snack at bedtime to avoid going low in the night.

So sorry about that. All that confusing math for nothing. But that’s the thing about diabetes: There are no simple questions. Thanks for writing, and keep your questions coming, people!

This is not a medical advice column. We are PWDs freely and openly sharing the wisdom of our collected experiences — ourbeen-there-done-thatknowledge from the trenches. Bottom Line: You still need the guidance and care of a licensed medical professional.

## FAQs

### How do you calculate insulin pens? ›

This means that JR will use 32 units of insulin each night (30 units for the injection, 2 units to prime the pen). **32 units x 30 days = 960 units**. If each pen holds 300 units, JR will need 4 insulin pens for the month.

**How do you calculate insulin pen day supply? ›**

To calculate the days' supply for insulin, first calculate the total number of units to be dispensed by multiplying the number of units per milliliter by the number of milliliters to be dispensed. Then divide the total number of units to be dispensed by the number of units prescribed per day.

**How many units is 3 mL of insulin pen? ›**

KwikPen (“Pen”) is a disposable pre-filled pen containing 3 ml (**300 units**, 100 units/ml) of insulin. You can give yourself multiple doses using one Pen. The Pen dials 1 unit at a time.

**How many doses of insulin are in a pen? ›**

Pens can contain **300 to 900 units** of insulin, depending on the device and the insulin concentration.

**How do you calculate insulin units in mL? ›**

Units to mL: **1 unit of insulin = 0.01 mL** (1/100) 20 units of insulin = 20 * 0.01 mL = 0.2 mL.

**What is one unit on an insulin pen? ›**

Insulin Guidance for School Nurse. The concentration of insulin is the number of units of insulin in one milliliter (mL). Insulin vials and pens commonly have a concentration of **100 units in 1 mL** (100 units/mL), which is called U-100.

**How do you calculate daily supply? ›**

For oral solids, including tablets and capsules, the day's supply calculation is fairly straightforward—if a patient is taking metformin 500 mg twice daily, **dividing the quantity prescriber by the number of doses taken per day** would give you the day's supply.

**How do you calculate days supply for Lantus pens? ›**

To work out how long one Lantus 10mL multiple dose vial will last you, you need to **divide 1000 units by your daily dose**. For example: If you are using 40 units a day. 1000÷40= 25 days.

**How do you calculate insulin meal time? ›**

To calculate your mealtime insulin, you need to **take the number of carbohydrate grams in your meal and divide it by the grams of carbohydrates covered by one unit of insulin**.

**How many units equal 1 mL? ›**

Insulin is measured in International Units (units); most insulin is U-100, which means that **100 units** of insulin are equal to 1 mL.

### Do insulin pens come in 1/2 units? ›

Most of the available pens in the market deliver insulin in 1 U increments, **a few deliver in half-units (0.5 U)**. Half-unit pens (HUPs), compared to 1 U pens, can further improve the accuracy and precision in insulin therapy^{13}.

**How long does a 3ml insulin pen last? ›**

Now, logically starting at the logical start, a 3ml pen of U-100 insulin has 300 units, as there are 100 units per mL, which is where the whole “U-100” thing comes from (3 x 100 = 300). So if you take 12 units per day, the pen should seemingly last **25 days** (300 ÷ 12 = 25), right?

**How many units are in a 100 mL insulin pen? ›**

Quick Links. Each ml contains 100 units insulin glargine* (equivalent to 3.64 mg). Each cartridge contains 3 ml of solution for injection, equivalent to 300 units.

**How long does each insulin pen last? ›**

Lilly insulin

Insulin Glargine (Basaglar®): Throw away pen/vials after **28 days**, even if it still has insulin left. Insulin Lispro (Humalog®): Throw away pen/vials after 28 days of use, even if there is still insulin left. Humulin R: Throw away vials after 31 days of use. If pen, throw away after 28 days.

**How many units of insulin are in a 200 mL pen? ›**

– The 200 units/mL pre-filled pen delivers **2–160 units** in steps of 2 units. Hypersensitivity to the active substance or to any of the excipients listed in section 6.1.

**What is 50 units of insulin in mL? ›**

0.5 mL syringes are for 30 to 50 units of insulin and are numbered at 1-unit intervals.

**How much is 1 IU of insulin? ›**

One IU (International Unit) corresponds to **0.035 mg** of anhydrous human insulin*.

**How many units of insulin are in a unit? ›**

Insulin vials have U-100 insulin. That means there are **100 units** of insulin in each milliliter (mL) of insulin.

**How much does 1 unit of insulin bring down sugar? ›**

One unit of insulin should cause your blood sugar level to drop **30 to 50 mg per dL**, but you may need more insulin to get the same effect.

**How many units Lantus per pen? ›**

Each ml contains 100 units insulin glargine* (equivalent to 3.64 mg). Each pen contains 3 ml of solution for injection, equivalent to **300 units**.

### How do you calculate Lantus needs? ›

If you have type 2 diabetes, your doctor will use weight-based dosing for Lantus. Your initial dose of Lantus will likely be **0.2 units of Lantus for every kilogram (kg)* of body weight**. The maximum starting dose of Lantus is 10 units per day.

**How many units are in a 10 ml vial of Lantus? ›**

Each ml contains 100 units insulin glargine* (equivalent to 3.64 mg). Each vial contains 5 ml of solution for injection, equivalent to 500 units, or 10 ml of solution for injection, equivalent to **1000 units**.

**What is the 500 rule for insulin? ›**

The 500 rule (500 divided by total daily insulin dose [TDD] of insulin) is **often used to find a starting point for the insulin to carbohydrate ratio (ICR)**, that is, how many grams of carbohydrate 1 unit of insulin covers, and this has been validated in children.

**What is a normal insulin level 2 hours after eating? ›**

These are typical targets: Before a meal: 80 to 130 mg/dL. Two hours after the start of a meal: **Less than 180 mg/dL**.

**What is the 450 rule for insulin? ›**

Alternatively, the insulin-to-carbohydrate ratio (ICR) may be determined by the "450 rule." To determine the ICR, **divide 450 by the child's total daily dose of insulin (TDD)**. For example, for a child with a TDD of 36 units, the ICR would be 450/36 = 12.5, or 1 unit per 12 g of carbohydrate.

**How much insulin should I take if my blood sugar is 250? ›**

If your premeal blood sugar level is between 121 and 170, or up to 50 points above the 120 mark, you'd take 1 extra unit of insulin; if it is between 171 and 220, or between 51 and 100 points above the 120 mark, you'd take 2 extra units; if it is between 221 and 270, or between 101 and 150 points above the 120 mark, ...

**How much is 30 units? ›**

30 units of a U-100 insulin are equal to **0.3 milliliters** (0.3 ml).

**How many units is a 10 mL vial of insulin? ›**

A typical vial of insulin contains 10 mL, or **1,000 "units"** of insulin.

**How many units are in a 1ml insulin syringe? ›**

Syringe size | Number of units the syringe holds |
---|---|

1/4 mL or 0.25 mL | 25 |

1/3 mL or 0.33 mL | 30 |

1/2 mL or 0.50 mL | 50 |

1 mL | 100 |

**Is 1 mL equal to 100 units on a syringe? ›**

**1.0ml syringe draws up to 100 units**.

### How many mL is 2 units? ›

Simply put, 1cc=1ml, 2cc=2ml, 3cc = 3ml, etc.

**How many units of insulin can you take at once? ›**

The right dose depends on your target blood sugar level, how many carbs you're eating, and how active you are. You might start with **four to six units of insulin**. Your dose may go up two to three units every 3 days until you reach your blood sugar target.

**What is the best insulin pen for Type 2 diabetes? ›**

**Tresiba** is a great long-acting insulin option. It can be used for blood sugar control in people with Type 1 or Type 2 diabetes. It lasts the longest compared to other long-acting insulins.

**How many units of insulin should I take a day type 1? ›**

Long-acting insulin can be administered once daily at bedtime or, ideally, twice daily in addition to another type of insulin. Patients with type 1 diabetes typically require an insulin dosage of **0.5 to 1.0 unit per kg per day**.

**What is 30 units of insulin? ›**

**0.3 mL syringes** are for insulin doses under 30 units of insulin and are numbered at 1-unit intervals. 0.5 mL syringes are for 30 to 50 units of insulin and are numbered at 1-unit intervals. 1.0 mL are for doses more than 50 units of insulin and are numbered at 2 units per interval.

**How many units are in 1 Lantus pen? ›**

Each ml contains 100 units insulin glargine* (equivalent to 3.64 mg). Each pen contains 3 ml of solution for injection, equivalent to **300 units**.

**How many mL is 30 units of insulin? ›**

30 units of a U-100 insulin are equal to **0.3 milliliters** (0.3 ml).

**How many units of insulin for 300 blood sugar? ›**

Blood glucose | 60–120 | 270–300 |
---|---|---|

Insulin correction | 0 units | 4 units |

**How much insulin should I take if my blood sugar is 400? ›**

Theoretically, to reduce 400 mg/dL blood sugar to about 100 mg/dL, you would need **at least 10 units** of insulin.

**How much insulin should I take if my blood sugar is 200? ›**

If your premeal blood sugar level is between 121 and 170, or up to 50 points above the 120 mark, you'd take 1 extra unit of insulin; if it is between 171 and 220, or between 51 and 100 points above the 120 mark, you'd take **2 extra units**; if it is between 221 and 270, or between 101 and 150 points above the 120 mark, ...

### How do you calculate prescription days? ›

**It just couldn't be easier!**

- Write down the date of your first dose.
- Add 29 days to the date you've just written.
- Obtained date is the last dose of your medication.
- The next refill period should begin the day after this date (+30 days).