Short answer: The insulin is usually the same; the device changes. The NIDDK says many people find pens easier but that they cost more. Labels say pens show the dose in units with no conversion, need a 2-unit prime or safety test before each injection, take a new needle each time and must never be shared. Opened pens often have different storage rules from vials, and labels say any change in how insulin is given needs medical supervision.
Many insulins come in both forms. The Humalog label lists U-100 Humalog in 10 mL and 3 mL vials, 3 mL cartridges and several 3 mL pens (KwikPen, Junior KwikPen, Tempo Pen), plus a concentrated U-200 KwikPen. Lantus comes as a 10 mL vial and the 3 mL SoloStar pen.
The NIDDK describes a pen as looking like a writing pen with a needle for its point; some come filled and are thrown away when empty. It says many people find pens easier to use, but they cost more than needles and syringes, and that a pen may suit people who find it hard to fill a syringe while holding the vial or to read syringe markings.
With a vial, the dose is drawn up to a line on a U-100 syringe. With a pen, it is dialed. The Humalog label says not to do any dose conversion with its pens: "The dose window shows the number of insulin units to be delivered and no conversion is needed."
| Pen | Steps | Most per injection |
|---|---|---|
| Humalog KwikPen and Tempo Pen | 1 unit | 60 units |
| Humalog Junior KwikPen | 0.5 unit | 30 units |
| Lantus SoloStar | 1 unit | 80 units (300 units per pen) |
The Humalog instructions say the pen will not let you dial more than the units left in it. The Lantus instructions say not to use a syringe to take Lantus out of the pen, and the Humalog label warns that moving U-200 insulin from a pen into a syringe can cause an overdose and severe low blood sugar because syringe markings will not measure it correctly.
An opened Lantus vial can stay in the fridge or at room temperature for 28 days, but an opened SoloStar pen is kept at room temperature only. Humalog pens in use are also kept at room temperature only. For Humulin N the gap is wider: an opened vial lasts 31 days, the KwikPen 14 days. The insulin gone bad page has the full table.
The Humalog label (section 5.2) says changes in an insulin regimen, including the method of giving it, may affect blood sugar control and lead to lows or highs. It says to make such changes under close medical supervision with more frequent glucose checks. The same section notes that a sudden move from lumpy, overused skin to fresh skin has been reported to cause lows.
Dose Track records each dose with its site and a note, so the first weeks on a pen can be compared with the vial weeks. The injection pen guide walks through the device itself.
Read more on Dose Track: How to use an injection pen · Insulin pen · Pen priming · U-100 syringe